MAJOR CLIMATIC EVENTS ASSOCIATED WITH A -INDUCED …

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ORAUlIEA 81 8(M)

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MAJOR CLIMATIC EVENTS ASSOCIATED WITH A PROLONGED CO2 -INDUCED WARMING

Hermann Flohn

October 1981

Institute for Energy Analysis Oak Ridge Associated Universities

Oak Ridge Tennessee 37830

Professor Emeritus University of Bonn Federal Republic of Germany

Research memorandums document substantive work in progress and receive internal review

This report is contribution number 81middot21 to the Carbon Dioxide Assessment Program It is based on work performed under contract number DEmiddotAC05middot760ROO033 between the US Department of Energy Office of Environmental Research and Development and Oak Ridge Associated Universities

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MAJOR CLIMATIC EVENTS ASSOCIATED WITH A PROLONGED CO -INDUCED WARMING2

ABSTRACT

The climates of earlier geologic times may provide useful analogues

for future cUmates tnat could follow global warming induced by CO2

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pnrticulnr two climatic events are possible if CO conrentrations reach2

levels ahove 600 ppm and if other greenhouse gases increase simultaneously

leading to an increase of 4-SoC in global average temperature One

- ~vent the disintegration of the West Antarctic ice sheet last occurred

about 120 thousand years ago The other the disappearance of the

shallow drift ice in the Arctic Ocean last occurred about 24 million

years ago Although this suggests that the West Antarctic ice is more

fr~gile than the Arctic sea ice the events may occur in the opposite

order Disappearance of the Arctic sea ice appears to require a shorter

preparation time during and after the temperature rise and hence may he

antIcipated first

The dislppearl1nce of the Arctic sea ice would constitute a case of

unl po lar glH La t i0n Paleoclimq tic ev idence suggests tha t the lltJ rtl has

fxperienced long periods of unipoIqr glaciation and that the effects of

Stich radicbull l asymmetry on global climate would be far-reaching Chief

among them would be shifts in the major climate zones especially a

northward displacement of the intertropical convergence zone and the

suhtropical anticyclones by 2deg or more This shift would produce seasonal

temperature and precipit~tion p8tterns-quite different from current

ones with si~nificant drying and warming in the 35-45degN latitude hAnd

Such changes could have serious implications for human activities

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TABLE OF CONTENTS

Page

1 Lntroduction bull bullbull 1

2 Existing Climatic Asymmetries bull 5

3 Pa leoe limat ic Evidence The Coexistence of an Ice-Free Arct ic

Ocean and an Ice-Covered Antarctic Continent I f)

3 I The Onset of the Tertiary Antarctic Glaciat ion I (I

12 The Mid-Tertiary rool Epochs 1 33 The Mid-Miocene Cooling Event n

34 The Messinian Peak of the Antarctic Glaciation and Its

Consequences bull bull bull bull bull 1middot1

35 Evolution of the Arctic Drift Ice and Contemporaneous Climatic

Events

4 Critical Thresholds and Time Scales of Possible Major Climatic

Events n

5 Towardgt 1 Climatic Scenario with an Ice-Free Arctic Ocean

6 SuggestIons for Further Research

Summary and Cone 1usions bull bull bull bull bull hi

App(mdlx bullbull

References 71

ii i

bull LIST OF TABLES

Tahle 1 Avernge Temperatures (OC) of the 700-300 mb Layer at the Polt nnd the ECJuator bull )

Table 2 Climatic Surface Oata from Antarctic and Arctic 7

Table 3 Energy Budget Components above the Arctic Ocean and the AntArctic Continent in Relative Units bull bull bull bull 8

Table 4 Observed and Estimated Values of rand 4gtSTA during Extreme S(Bsons (rgtorthern Hemisphere) bull bull bull bull bull 4 I

Table 5 Estimated Changes of r under Different Assumptions and Resulting Latitudes of Subtropical Anticyclones 41

ra b Ie A-I Model-Dependent Sensitivity Parameters h7

v

LIST OF FIGURES

FigUTlt L Seasonal vnriatinn of latitude of sIJbtropic11 anticyclones (ltlSTA) versuS temperature difference between the equator and the poles (tT) at the 700-300 mb layer both hemispheres 10

Figure 2 Relation between average isobaric temperature gradient and latitude of subtropical anticyclones for different vertical lapse rates y bullbullbull 11

FirlIre 1 Seasonal variation of the meteorological equator a)onR long 25degW 12

- Figure 4 Monthly averages of sea temperature along long l40W

(central Pacific) at a depth of 300 ft (91 m) ])

Pi )(urlt 5 Long-term trends of SST and bottom water temperatures in the subantarctic ocean (about lat 50 c S long 160 0 E) during t he las t 58 Ma bull bull bull bull bull I H

Figure o A terrestrial ring system hypothesized to have cirded the enrth about 38 Ma ago (after J OKeefe 1980) and its shadow on the earth present position of America for comparison 2(J

Figure 7 Long-term trend of SST in the North Sea area isotopically 21derived from mollusk shells

l8Figure 8 Time series of a 0 as representing global ice volume during the IClst 35 Ma n

figUT( 9 reneralized patterns of main climatic belts at an idealized - (ontinent (center) and adjacent oceans (Flohn 1981) at present

and during late Tertiary bull 4h

Figllre JO Zonill1y averlged values of the difference between preshycipitation and evaporation on land after Manabe and Wetheralds (19RO) general circulation model with different CO levelA

2

Firurp 11 Evidence for tbe displacement uf the northern boundary or the Northern Hemisphere arid zone (evaporite sediments) during early Tertiary (50-30 Ma ago) IClte Tertiary (1)-5 Ma ago) nnd Pleistocene (2-0 Ma ago) bullbullbullbullbullbullbullbull bull bull bull bull bullbull ~H

vii

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bullfigtlrt 12 Annual trend of evaporation (mmmonth) Jat 20oN-1OS along the shipping route Europe-South Africa eastern Atlantic )1

Figllrl n SST along long 140a W (central Pacific) monthly avernges from maps hy Robinson (1976) bullbull bull bull bull ~j

[i)llrtmiddot llL Projected changes of mlntlal surtacE temperature (left inC) and annual precipitation (right t of present) in the (ltlSt of an ice-free Arct ic ) 1

FIgure A-I Atmospheric CO) and surface temperature change bull ()

III II III

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ACKNOWLEDGMENTS

This report was written during my two-month residence at the Institute

for Energy Analysis Oak Ridge Associated Universities Oak Ridge Tennessee as

a Mel ton Distinguished Fellow 1 am especially indebted to Relph M Rotty

and to other memhers of the Institute staff among them C F Baes Jr

P R Re]l W C Clark K F Cook and G Marland for stimulating disshy

clIssions Th1nks should lIsa be extended to T J Blasing P A Delcourt

ff R f)plcolJrt and 1 S Olson all of Oak Ridge National Laboratory and

to R r Watts a visiting scholar at the Institute from Tulane University

~ose h~lp was indispensable for the appendix table ~arianne Fisher typed

the manuscript Ethel Ayres prepared the drawings and Vivian Joyce and

LfndB Allison were particularly helpful during my stay

CHAPTER 1

I NTRODUCT ION

Two different approaches are available for examining the possible transishy

tion to a warmer climate that may follow an increase of atmospheric CO content2

(1) we may develop ~limatic models of the atmosphere-ocean-ice-biota system

or (2) we may seek Raleoclimatic analogues of past warmer climates Each

approach has advantages and disadvantages Early models based on prescribed

sea surface temperatures (SST) and the amount of cloud cover gave a fairly

adequate description of the tropospheric climate if one disregarded the fact

~hat SST and clouds are variable elements of a climate and should not be reshy

garded as its boundary conditions Even with such models the surface climate

which depends on surface albedo soil moisture and other heat budget terms

with marked local and regional peculiarities is not as well described as the

mid-tropospheric circulation Not only the interaction between clouds and

radiation hut also the interaction between ocean and atmosphere has yet to be

satisfactorily integrated into the more advanced models Air-sea interaction

op(rates hoth through evaporation (as in a swamp model eg Manabe and

Wpthrrald 1980) and through heat storage both long term and seasonal (as in a

lItxed ocron 1Ryer modl eg Manabe and Stouffer 1979 and 1980) The

dynamics of the ocean driven by wind stress and--at greater depths--by thermoshy

halinf forcing functions has to be included (eg Manabe Bryan and Spellmnn

)79 Washington et al bull 1980) because of the strong effect on climate This

statement is particularly true for the baroclinic western boundary currents

such as Gu] f StreRm and Kuroshio and for the regions of equatorial and coastal

upwelling the latter topic will be treated in more detail in Chapters 2 and 6

Th~ great Rdvantages of climate models are flexibility adaptability to

different questions and their horizontal resolution their promise for the

future is certainly greater thqn the results already published fascinating as

those results are Their disarlvantages include the lack of ocean data to

verify the variability of ocean patterns (eg the role of oceanic eddies in

transporting heat) and the lack of test cases for verification of climatic

patterns different from the existing ones An adequate simulation of seasonal

fluctultions is a necessary bllt not sufficient test case

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2 II II II IIwith sufficient horizontal and vertical (Le time) resolution to allow for

mapping past lIIllHtes as for example during the CLIMAP program for the last

glI(illlon IF ka (ka = 1000 years) ago Nevertheless such analoguEs as bullmiddotxampltmiddots of redl events from the past can be rather useful in constructing

seenlr i()~ for impac t studies The change of bOLlndary conditions between tilt

time of the analogue and the present is comparable in most cases to the role

of simplifications applied in running a climate model

Some paleoclimates as possible analogues of the future have been tudiEd

i~etail the Holocene hypsithermal (Kellogg 1977 Sarnrhein 1978 radolson

and Flohn 1980) the peak of the last glaciation (CLIMAP Project MemhErs bull1976 Sarnthein 1978 Peterson et al 1980) and the last interglacial the

Eem (c f DansgaarJ and Duples sy in press) Except for the first two excr)~ 1es it

is extreme ly d ifficu 1t to obtain enough quantif iable data to complete 1 reasonshy -shyable milp (Pg of the past land vegetation as an indicator of past cUmarf)

This difficulty especially applies if one tries to outline the climate of the bull late Tertiarv that is the period before the first onset of a large-sLule

6glaciation of the northern continents about 33 Ma (Ma = 10 years) ago

(Shackleton and Opdyke 1977)

In recent years ocean-core drilling (for example the Deep Sea Drilling

Program or DSDP) has revealed some really amazing facts of geologic and

~H)oclimatic history We have learned for example that an Antarctic

glaciat1on simultaneous with a dramatic global cooling started at the boundshy

ary between the Eocene and Oligocene epochs about 38 Ma ago (Kennett 1977)

The ear ly Otcurrence of this Antarctic glaciation is in sharp contrast to the

much laumiddotr glaciat ion of the northern continents which was follmved by the

evolution of [he drlft lee of the Arctic Ocean (Herman and Hopkins 1980)

Drift ice be~an a~ ~ seasonal phenomenon probably 24 Ma ago and became a

perennial fti1ture at the boundary between the paleomagnetica1 epochs Matuyama

and Hnll1hes lhout 700 ka ago

A complete ice cap covering Eastern Antarctica was formed (Kennett 1977)

durillg the mid-Miocene about 15-13 Ma ago after a period of extensive bull

Paleoclimatic analogues on the other hand have one advantage they

represent realistic solutions of the complete set of equations that only nature

can solve on-line and in her own time Their main disadvantages are the

chanlls in boundary conditions over time (eg changes of atmospheric composishy

tion of sea level and of mountain building) and the frequent lack of evidence

3

volcanic activity (Kennett et al 1977) it gradually expanded to Western

Antarctica during the late Miocene By this time the volume of the continental

Antarctic ice sheet must have been up to 50 percent greater than it is now--as

evidenced by isotopic data from benthic foraminifera by the ice-formed mountains

above the present top of the ice sheet and by the advance of thick shelf ice

up to the edge of the continental shelf some 300 km north of its present position

(for details see Chapter 3)

Thus during a period of at least 10 Ma the Antarctic continent was

heavily glaciated while the Arctic Ocean must have been ice-free From the

vifgtWpoint of climatic history this fascinating example of a unipolar glacishy

ation provides insights into the climatological consequences of a unipolar

warm period Budyko has suggested (1962 1969 1977) that in the foreseeable

~uture the Arctic Ocean might again become ice free possibly as a consequence

of a rising CO concentration of the atmosphere (see Chapter 4) Some climatic2

consequences of such an asynnnetric pattern have already been outlined (Flohn

197Rb 1979 1980) and will be expanded further in this paper

Indeed this late Tertiary period is not the first example of a unipolar

glaciation During the late Paleozoic (around 240 Ma ago Frakes 1979) the

Southern Hemisphere with its giant supercontinent (Gondwana)--consisting of

Africa Allstrailia Antarctica and the larger portions of South America and

India--was at least partly glaciated for 10-40 Ma probably longer Simulshy

taneotlsly the continents of the Northern Hemisphere were situated in a preshy

dominantly oceanic environment with a moist subtropical or tropical climate

maintaining extended forest swamps Most of our present coal reserves were

roduced in North America Europe and China at this time no evidence points

towards a northern glaciation during this period

In contrast to this earlier unipolar climatic pattern the earth enjoyed

during the Mesozoic and the early Cenozoic (a long period of 200-40 Ma ago) a

hipolar warm climate without traces of ice or snow at either nolar rev-ion

(Frakes 1979) For this pattern the term acryogenic has been Hllggested

At first glance such a bipolar Wlrm pattern appears more understmdable

thfln a unipolar pattern But a certain degree of asymmetry (Chapter 2) is

indeed characteristic of our existing climate its geophysical background

depends mainly on the varying land-sea distribution during the tectonic history

of the earth which almost certainly allows for both patterns

4

Chapter 2 presents the geophysical factors that control the present

asymmetry of climatic patterns in the atmosphere and oceans Chapter 3 gives a

(necessarily incomplete) review of the evidence available for the climates of

the Oligocene Miocene and early Pliocene (about 38-3 Ma ago) In Chapter 4

an attempt is made to identify a critical level of the atmospheric CO expected2

to produce two outstanding climatic events based on the results of experiments

with present climatic models In Chapter 5 available paleoclimatic data are

used to outline a possible climatic scenario under present boundary conditions

for a CO -induced warming beyond the critical threshold Chapter 6 gives a few2

suggestions for modeling this type of asymmetric climatic pattern and some

conclusions are summarized in Chapter 7 The report is partly based on the

relevant chapters of an earlier report (Flohn 1980) submitted to the Intershy

~ional Institute for Applied Systems Analysis (IIASA) in Laxenburg Austria

but includes much additional data and recent investigations

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CHAPTER 2

EXISTING CLIMATIC ASYMMETRIES

The asymmetry of the global atmospheric circulation--and consequently of

the wind-driven mixed ocean layer--stems from the fact that the North Pole is

situated at a nearly (85 percent) landlocked deep ocean with a thin broken

drift ice cover while the South Pole is situated on the isolated Antarctic

continent which is covered by a thick ice sheet Available radiosonde data

from the South Pole and from drifting ice stations in the Arctic (data from

the US and from the USSR differed only by a few tenths of a degree) have

~been compared with a chain of temperature data from the meteorological equator

lat a-lOoN (Flohn 1967 1978a) The average temperatures are compared in

Table 1

Table 1 Average Temperatures (OC) of the 700-300 mb Layer at the Poles and the Equator

Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477

Difference E-N 329 173 273

Difference E-S 297 441 191

Note Data had been derived from 5-R years of (carefully selected and coherent) radiosonde data

The mid-tropospheric layer (700-300 mb) had to be taken since the South

Pole is situated at an qltitude of 2700 m with a surface pressure near JAO mb

therp is no way of estimating temperatures below that level The data of

Tahle I are slightly biased hecause at the South Pole the shallow but intense

(during winter) surface inversion has been included while the weaker Arctic

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6 III surface inversion has been neglected Nevertheless the annual difference of II mid-tropospheric temperatures between the two poles is remarkable high (ll~OC)

the January temperatures are nearly equal and the difference increases to

nearly 27degC in July Above the surface inversion the annllal differences are

only slightly below 11degC Surface climates are similarly different Here

only a few characteristic examples can be given (Table 2)

The physical reason for these remarkable differences should be seen in

the Tlther different terms of the heat and radiation budget (Table 3) The

essential differences He the higher albedo of the Antarctic surface the

Ilfghcr cloudirwss of the Arctic and its higher temperatures resultinH in the

hj~lHr outgoing infrared radiation at the top of the atmosphere The horizonshy

tal advection of heat to the Arctic is about twice as high as that to the

Antarctic mainly due to quasistationary eddies caused by the land-sea disshy

ibut ion in middle lat itudes The oceanic heat advection is probably undershy

estimated Aagard and Greisman (1975) estimated a value of 106 Wm2 instead 2of I 7 Wm given by Vowinckel and Orvig Fluxes of the combination of sen-

AlbIe and latent heat are opposite at the two poles the atmosphere is heated

from the Arctic Ocean through the narrow leads and the polynyas between the

ice floes but the atmosphere transports heat and water vapor down to the

~xtremply cold surface of the Antarctic ice sheet

In both polar regions the negative radiation bud~et is maintained hv the

atmospheric advection of warmer air with only a minor contribution by the

ocean where the warm Atlantic water submerges below a cold but less saline

([lnd thus less dense) surface layer In spite of the higher input of solar

radiation during the southern summer (even though earth distance is up to 7

~middotcpnt higher than during northern summer) the air above Antarctica is colder

than the air above the Arctic This difference results primadly from Antarcticas

high albedo and complete isolation which produce a zonal flow of westerlies

around it and thus reduce the horizontal advection of warm air

The climatic consequences of tllis thermal asymmetry are expressed bv

one of the fundamental parameters of atmospheric circulation the thermal

ROSSDY number ROT

=

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( ( Table 2 Climatic Surface Data From Antarctic and Arctic

Height TemEeratures (OC) Cloudiness () Station (m) Summer Winter Annual Abs Extremes Summer Winter Period

South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66

Greenland Eismitte (71degN) 3000 -139 -397 -288 -3-65 65 51 1930-31 1949-51

bArctic Ice Drift (80-88degN)a 2 -10 -337 -192 +6-51 90 51 1957-61

Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56

aSeveral drifting stations partly simultaneous together 117 months

bFrom drift 1893-96 annual average also -192degC

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8 bull Table 3 Energy Budget Components above the Arctic Ocean and the

Antarctic Continent in Relative Units bullII

Arc

Radiation

Extraterrestrial solar radiation 100 100 Reflected solar radiation from

surface -30 -65 Reflected solar radiation from bull

clouds -33 -16 Absorbed solar radiat ion in the

atmosphere +14 +6 -bull((Absorbed solar radiation at the surface +23 +13

Outgoing infrared radiation top bullDE atmosphere -98 -46

Heat

Flux of sensible and latent heat into the atmosphere +5 -5

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Oceanic heat advection to surface +6 a Atmospheric heat advection +55 +27 bullE~ergy balance of an atmospheric column at the top

Arctic Ocean 100 + 55 + 6 - 98 - 30 - 33 = a Antarctic Continent 100 + 27 - 46 - 65 - 16 = a bull

bullbullbull t Source All data are best available area-averaged estimates but subject

to different sources of error probably 10-20 percent they have been only slightly adjusted to a zero energy balance Flohn 1978 data after E Vowinckel and S Orvig and W Schwerdtfeger ~orld Surv~of Climatology Vol 14 (1970) bull

I I I I

9

auHere U is the vertical shear of the zonal wind u (ie az 6l) and is pro-

T portional to the meridional temperature gradient (aTJay) given here in the

hemispheric differences E-S and E-N in Table 1 r is the radius of the earth

and n is the angular speed of its rotation This dimensionless number ROT

describes the zonal thermal wind depending on the temperature differences

between equator and poles in units of the rotational speed of a point on the lequator (464 ms- ) In July the thermal Rossby number above the Southern

j

Hemisphere is about 25 Simes higher thlln abovp the Northern Hemisphere and

t h~ annual avprage is bout 40 percent higher

Even more fundamental is the famous circulation theorem formulated by V

B1erknes in 1897 In simplified terms this theorem states that the intensity

of a circulation within a rotating atmosphere depends on the rotation speed

~ above) on the horizontal temperature gradient and on the vertical lapse

rate The last term depends largely on atmospheric composition especially on

the amounts of water vapor and carbon dioxide Several model investigations

suggest that the stability of the troposphere decreases with increasing CO2 content (Manabe and Wetherald 1975 1980) but the role of clouds has not

heen fully established in these models

The role of the horizontal temperature gradient is of particular imshy

portance to the stability or instability of eddies within baroclinic currents

or rhe atmosphere Smagorinsky (1963) has provided a criterion for the baroelnic

instability that is related to Bjerknes circulation theorem and depends on

latitude Smagorinskys Z-criterion is a relation that allows an estimate of

the boundary between the unstable extratropical Ferrel circulation and the

stable tropical Hadley regime (ie the subtropical anticyclonic belt)

(F n 1964) This boundary coincides quite well with the center of the

subtropical jet If we assume the vertical lapse rate to remain constant the

stability of the eddies is controlled by the meridional temperature gradilmiddotnt

Since the eddies tend to be unstable in the Ferrel circulation but stable in

the Hadley cell where the horizontal gradients are usually quite weak then

the latitude-dependent threshold of the Z-crlterion gives a good estimate for

thp seasolllt1l1y varying latitude 4 of the subtropical anticyclonlr hrmiddotltSTA

bull anJ 1y= cos ltyenSTA h JoJaz

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where h is the scale height of the bull

y the meridional ~oordinate and z

concept has been verified hy Korff

700-)00 mb I aver at each hemisphere

10

atmosphere 8 the potential temperature

is the vertical coordinate This theoretical

and Flohn (19119) IIsin monthly data for the

(from Flohn 1967) and for

lvcrilJes of sllrfa~e pressure (from Phlugbeil 1967) from which

P of the pressure maxima has been simply interpolated (UseSTA

function could probably have improved the result slightly but

datil nT not quite synchronous and of different length and give

15

Figure 1 Seasonal versus pmperature

the latitudinal

the latitude

of a mathematical

the sets of

thus only a

reJ-wnabIe guess) Figure 1 shows (with a few minor differences from an

Pllrl i(r figure in Korff and Flohn 1969) the annual course of 4lSTA and the

equator-to-po1e temperature differences for the 7nO-300 mb layer for each hemishy

sphere During the northern wintersouthern surmner (December-February) the

middotllufs for the two hemispheres are approximately equal but during the northern

~mmersouthern winter (June-August) the difference between the values reaches

Its maximum Nevertheless the correlation coefficient of the 24 pairs 1s

qult~ high (+085) Lf one allows as in many climatological relations a

month lag Iwtween the t(mperature gradient and the parameter 1gtSTA derived

OAAU1756

Mx

e-e Northern Hemiaphere II bullbullbull 1I Southern Hemisphere reg reg Annual AvelllCle

r shy 0865

20 25 30 36 40 45

oneshy

from

t T at 700-300 mb degc

variation of latitude of subtropical anticyclones (ltPSTA ) difference between the equator and the poles (6T) at tfie

700-300 mb layer both hemispheres vertical scale = cot dl (revised afterSTAKorff and Flohn 1969)

_

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11

the pressure field the correlation rises to 092 The annually averaged

positions of ~STA are near 36degN and 3l o S

For several reasons this simple empirical relationship is preferable to

the curves shown in Figure 2 and derived from Smagorinskys criterion (Flohn

1964) for different values of the vertical lapse ratey Whether the meridional

temperature gradient in the formula above can be taken simply as a linear

average between equator and pole or perhaps as the highest value in the

subtropical baroclinic zone is highly uncertain (Flohn 1964) Secondly the

vertical lapse rate in CO -climate models varies considerably with the parameters2given to the cloud-radiation interaction The future role is not clear

since in most latitudes (except polar ones) the lapse rate is nearly moistshy

diabatic only minor changes toward higher instability should be expected

rt shu II come back to this relationship in Chapter 5

OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg

8deg 10deg aTla y (isobar) (oCl000 km)

figure 2 RelDtion between average isobaric temperature gradient and latitude of subtropical anticyclones for different vertical lapse rates (Flohn 1964)

Under existing conditions the climatic asymmetry of the two hemispheres

is responsible for a whole set of climatic phenomena Here only the most

important features are outlined

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1 In the Southern Hemisphere the intensities of both the surface

westerlies Hnd the tropical easterlies are greater than in the Northern

Hemisphere

2 Two distinct baroc1inic zones coexist in the southern westerlies

one if a suhtropical jetstream near lat 25-30 0 S and the other a polar

cJrcum-Antarctic Jetstream at lat 50-60 0 S (van Loon et a1 1972) In

the Northern Hemisphere the two zones frequently (and regularly in some

sections) merge

3 Because of the higher intensity of the southern circulations the

HOIIIIIIrn I rilllt IlHI Ily lxttnd north or the (fJuator laquoX(middot~Pt durlnJ northtrn

Wlnlr) lntl push the annual average locntion of thEgt main intertropical conshy

vergence zone (ITCZ which is the equatorial trough) to lat 6degN during

nthern summer the location averages about l2degN (longitudinally averagpd)

4 The average position of the ITCZ (meteorological equator with a

maximum sea surface temperature a maximum of convective activity and a

reversal of meridional wind components) north of the mathematical equator

leads to a displacement of the oceanic equatorial rain belt to lat 0-12degN

(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )

J F M A M J J A s o N o J

Figure 3 Seasonal variation of the ~eteorolo~ical equator along long 25 0 W (central Atlantic surfacedata after Kuhlbrout E42 internal report) Tw = maXlmurn of SST v shift of mericional wind component (shift from II to S) ~ peak of thunderstorm frequency R = peak of rainfnll frequency circle average of these four parameters

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13

5 At many climatic stations between the equator and lat SON the

encroachment of the southern trades is accompanied by an advective temperature

minimum in northern summer (Sudanese type of annual trenrl)

o Another quite important consequenc~ is oceanic upwelling near the

equator we shall come back to this topic in Chapter 5 The asynnnetry is

llBO demonAtrated in the narrow eastward flowing equatorial countercurrent

(lat 2-8degN) which has a marked baroclinic structure (Figure 4)

The origin of the asymmetry outlined above may be found in the geographical

differences Antarctica is a continent thermally isolated by a strong baroclinic

circum-Antarctic ocean current By contrast the Arctic Ocean has only one

major (Atlantic) and one minor connection with the major oceans and is A5 pershy

-nt encircled by continents although its water masses exchange meridionally

with other oceans

OAAU 81112

AVERAGE TEMPERATURES (OC) AT A DEPTH OF 300 ft = 91 m AT LONGITUDE 140deg W

N

12

8

o

-4 5

Figure 4 Monthly averages of sea temperature along long 1400W (central Pacific) at a depth of 300 ft (91 m) (from maps by Robinson 1976) Note the strong temperature gradient between about lat 5deg and lOON (equivalent to the baroclinic equatorial countercurrent) the cold equatorial trough and the much colder trough at lat 8-11oN (see also Wyrtki et al 1981)

Jan Feb Mar Apr May June July Aug Sept Oct Noy Dec Jan

II

I

CHAPTER 3

PALEOCLIMATIC EVIDENCE THE COEXISTENCE OF AN ICE-FREE

ARCTIC OCEAN AND AN ICE-COVERED ANTARCTIC CONTINENT

M I Budyko (1962 1969) was the first to suggest that the thin Arctic

Mea lee with its many leads and polynyas is highly sensitive and may disappear

under special climatic conditions In these early papers Budyko did not

discuss in detail the contrasting apparent stability of the Antarctic ice

sheet Little was known about the history of either polar ice cap at that

time Since then the very existence of Antarctic ice has served as a strong

argument against the possibility of a perennially ice-free Arctic Nevertheshy

less a perennially ice-free Arctic has been presented as a remote future

~ssibility (eg SMIC Report 1971)

As discussed in Chapter 2 the recent discovery of the early date of the

glaciation of the Antarctic relative to the glaciation of the northern continents

establishes that a long period of unipolar glaciation indeed existed 1bis

unlpolar glaciation must have led to a marked asymmetry of the earthls climate

espeliillly or thC enerl1i circulation of the atmosphere and the oceans (Flohn

J97iia 1979) [Ill 1symmptry much more pronounced than the prespn t om In tlti~

chapter the hiRtory of this evolution is reviewed bv means of a (necessarily

incomplete) compararive assessment of the available literature This review

will serve as a hase to outline the climatic pattern during the final ner10d

of this era of unipolar glaciation when the climatic boundary conditions

(flg land-sea distribution mountain building) most nearly approximated the

sent ones

Thus the following (more or less sequential) time-sections will be

investigilterl

1 Thegt Eocene clim1te during which the Antarctic glaciiltion bcgnn lOU

tIl( urmnntic cooling ]ssociated with the terminal Eocene event

2 111(gt mid-Tertiary cool epoch (Oligocene early Miocene)

30 The mid-Miocene event and the formation of il fully dveloped ice

sheet over ERst Antarctica

4 The apparent peak of Antarctic glaciation and the Messinian salinity

crisis

5 The development of large-scale glaciation on the northern continents

and the evolution of the Arctic sea ice

l6

31 The Onset of the Tertiary Antarctic Glaciation

A few ice-rafted quartz grains in ocean piston cores indicate the beginning

of local glaciation on the Antarctic continent during the Eocene epoch (55-38

Ma ago) At this time Antarctica was situated in about the same latitude

as now its margins were connected with the plates of Australia and New Zealand

both then at highly southern latitudes (Coleman 1980) During the early

Eoc~ne Australia began to drift northward at first together with New Zealand

at some times with the remarkably high speed of 7-8 cm ~er year A shallow

gulf opened to its south and gradually developed into a broad epicontinental

channel which isolated--from the viewpoint of climatology--the Antarctic

co~inent The following review is mainly based on Kennetts (1977) report

together with the history of ocean circulation given by Berggren and Hollister

(1977) A recent review on the paleopositions of drifting continents has been

presented by Habicht (1979)

Near Australia (Raven and Axelrod 1972 Kemp 1978) water temperatures

in the southern channel--which was sometimes closed by a land bridge connecting

the Tasman rise with Antarctica and the surrounding subantarctic seas--had

been estimated at about 19degC in the early Eocene gradually dropping to 11degC

in the late Eocene (Kennett 1980) Ice-rafted grains in Pacific cores suggest

an early onset of mountain glaciers in Antarctica simultaneous with rather

highly developed cool-temperate coastal vegetation In Australia (which lay

between lat 30deg and 58degS 45 Ma ago) evidence points to warm-temperate even

tropical vegetation (Kemp 1978) humid even in the center of the continent

Ap~ently these forests have no modern analogue they contained a mixture of

tropical and temperate trees (like nearly simultaneous Eocene flora from

London) However this statement is based on the conjecture that the adaptivity

of these trees to climatic conditions has remained unaltered There is overshy

whelming evidence for high humidity at all of the Eocene sites (south of

paleolatitude 40deg5 see Kemp 1978) and most of the data suggest rain forest

The high temperatures and humidities of Australia and to a lesser degree

AntarctIca could have been caused by the contemporaneous drift of India towards

the north which deflected the early equatorial Pacific current towards the

south (Berggren and Hollister 1977)

bullbullbullbull ( bullbull bullbullbullbull

bullbullf

bullbullbullbullbullbullbull

17

The history of the Arctic Ocean is less well understood a narrow channel

may have connected it with the Atlantic via the Labrador Sea while the status

of the Hering land bridge during that time seems to be uncertain A Protoshy

Gulfstreilm (Gradstein and Srivastava 1980) carried warm water from the

Atlantic into the Arctic Ocean

In the Eocene a rich warm-temperate partly coal-producing flora occupied

even the northernmost Arctic islands such as Svalbard (Spitsbergen cf

Schweitzer 1980) and Ellesmere-Land (McKenna 1980) The paleolatitudes were

not significantly different from the present ones Toe climate of the Arctic

resembled then that of southern China and the southeastern US today with

annual averages of IS-18degC no (or only rare) freezing during winter and marine

~eotemperatures also reaching 15degC locally (McKenna) The fauna was similarly

rich (Estes and Hutchison 1980 McKenna) including such reptiles as varanids

alligators and mammals Wolfe (1978 1980) has suggested that a reduction of

the tilt of the earths spin axis with respect to its orbital plane (obliquity)

to values of only 5-10deg (now 23deg) caused this mild climate Such a change

should have greatly reduced the seasonality of the climate and increased the

zonality (ie the meridional temperature difference between the equator and

the poles) However this hypothesis--for which no physical interpretation

has been given--is hardly consistent with the pattern of growth rings in

trees Most evidence suggests a smaller meridional gradient Thus it seems more

probable (Estes and Hutchison) that some vertebrates had adapted to the winter

dormancy now typical for the dark period in subarctic and temperate latitudes

The climate model suggested by Donn and Shaw (1977)--neglecting any kind

~climatic feedback--is also inconsistent with observed facts From considerashy

tions described in Chapter 2 it had been suggested (Flohn 1964) that during

the Mesozoic and early Tertiary (ie under the condition of a bipolar warm

climate with both poles ice-free) the tropical Hadley circulation extended to

lat 50-60deg (as the latitude of the subtropical anticyclonic belt) Then

only a comparatively small polar cap should have been controlled by a Ferrelshy

type polar vortex with westerly winds and average temperatures not below 10degC

This model would also be consistent with a constant angular momentum (Lamb

1972 Kemp 1978) if we assume quite weak easterlies within the broad Hadley

cell which may also have shifted considerably with seasons Berggren and

Hollister (1977) have also indicated a slow sluggish ocean circulation during

this bipolar warm climate

bullbullbull

c- bull-- bullbull --

(I UP W

18

The boundary between Eocene and Oligocene about 38 Ma ago is charactershy

ized in many marine deposits from over the globe by a remarkable drop in bull bottom water ltmd sea surface temperatures of 4-5degC (see Fig 5 from Flohn

19HO HlaptCd from Kennett 1977) This major rapid global cooling has been

connected with a widespread gLlciation of East Antarctica at sea level (Kennett

1977 L9HO) and with extensive production of sea ice and of Antarctic bottom

water with temperatures near +5degC The drop in bottom water temperature

initiated the present abyssal circulation and led to a dramatic change in the

benthic fauna which spread rather rapidly (on geological time scales) over

all deep ocean basins including the Mediterranean which was then a part of

the circumtropical Tethys Sea (Berggren and Hollister 1977) Another important

-

~~~- -

-bull lt

- Bottom Water Temperature

Surface Water Temperature

Eocene

~----~------~----~~----~-----

- 55)( 106 yr ago Paleocene

20degC

Figure 5 Long-ternl trends of SST and bottom water temperatur~s in the subantarctic ocean (about lat 50 0 S long 160degC) during the lasl 58 Mi1 (comhined after Kennett 1977) Note Lht SlIudCn drops at 3 Ma and 14 ~1a ago and the incrtase of the vertical temperature difference during the last 20 Ma The (isotopic) bottom water temperature data reflect before about 20 Mltgt the surface temperatures along the Antarctic coast after that date they are biased by the varying degree of obal continental ice volume

ORAU Bl 1 1015

Pleistocene

jocene - 5 x 106 yrs ago

late Miocene

Mid-Miocene - 14 x 106 yrs ago

Early Miocene

- 22 x 106 yn ago

bullbullbull1(

bullbullbullbull bullbullbullbullbullbullIII

19

consequence was (cf Keigwin 1980) a sudden drop in the calcite compensation

depth of 1-2 km which affected the CO budget of the oceans An alternative2

interpretation for this depth change given by Thierstein and Berger (1978) is

not u iHusRed here since it seems to he a t variance with the results of

Eldholm and Thiede (1980) In the North Sea area a marked drop of temperatures 18is indicated by isotopic data from many fossil shells A rise in 0 0 of more

than +3 percent has been observed Assuming that the salinity of this shelf

sea varied only within limits of 33-37deg00 (Buchardt 1978) this would be

equivalent to a temperature drop of l2(plusmn4)OC

Paleobotanical evidence also indicates a dramatic cooling (Wolfe 1978

1980) which has been associated with the terminal Eocene event Wolfe esti shy

~3ted the decline in mean annual temperature to 12-13degC at lat 60 0 N (the Gulf

of Alaska) and 10-11 degc at Iat 45deg in the Pacific Northwest of the United

States The mean annual range of temperature had increased from 3 to 5degC

in the middle Eocene to at least 20degC and probably as high as 25degC by the end

of the epoch (Wolfe 1978) Although a climatologist cannot judge the validity

of the concept on which these estimates are based they appear to be compatible

with the other data mentioned Wolfes date of 34 Na ago should be comparable

to 38 Ma as derived from Deep Sea Drilling Program data

J A OKeefe (1980) has contributed a remarkable interpretation from the

astronomical viewpoint that may support all of the data mentioned He starts

from the observation that at about the time of this terminal Eocene event 9 a very large field of tektites with an estimated mass of 1-10 Gt (10 tons)

was spread over the worlds tropical belt from the Caribbean through the

~ntral Pacific to the Indian Ocean Given the low sedimentation rate in this

region of 05-1 cm per thousand years the coincidence between the sharp peak

of microtektites and the extinction of five species of radiolaria in a core

from the Caribbean is indeed convincing (his Fig 1) OKeefe suggests that

these tektites (of cosmic origin) indicate that an even larger mass of microshy

particles missed the earth and were trapped in a geocentric orbit like the

rings around Saturn and Jupiter possibly at a distance of 15-25 times the

earths radius Such a ring necessarily oriented in an equatorial plane

might have reduced the sunlight received by the earths surface by nearly 75

percent with an assumed vertical optical depth of 03 assuming a total mass 22of 25 Gt produced about 2 x 10 particles of 100 urn Such a ring is estimated

20

to -last a few million years Its main climatic effect would be (Figure 6)

a drastic reduction of wintertime radiation in each hemisphere together with

no effect during summer In tropical latitudes a strong shadow effect would

cover only a narrow band shifting seasonally with latitude without model

investigations it would be premature to estimate its climatic effect This

conjecture would indeed suggest a drastic increase of both seasonality and

presumably also zonality of the climate How far this hypothesis is indeed

compatible with the bulk of the available evidence remains to be seen (cf bullalso section 33)

OR AU 81752

--~- --shySlIIlitl

Figure 6 A terrestrial ring system hypothesized have circled the earth about 38 Ha apo (after J

bull bull

e bull III

to bullQKtefc III1930) and its shadow on the earth present posit jon of

Arlerica for comparison jbove winter solstice ring shadow only at high norther latitudes (summer solstice similar but shadow at high southern latitudes) Center solar declination - lLo ring shadow in subtropical latishytudes Below solar equinoxes narrow ring shadow at bullthe equator high latitu~es not affected bull

21

32 The Mid-Tertiary Cool Epochs

Of minor importance within the context of this report are the Oligocene

and Miocene epochs which covered more than 20 Ma (38-16 Ma ago) The climate

of this period was almost certainly controlled by the coexistence of an Antarctic

continent probably still partially glaciated (though the evidence is not

strong) and an ice-free Arctic This unipolar climate however occurred

when the climatic boundary conditions (eg the distribution of land and sea

and mountain building) differed significantly from the present pattern (Berggren

and Hollister 1977 Habicht 1979) These differences are not discussed in

this short review

~ Two important features of the climate however ought to be mentioned

here The first is a general rather drastic cooling of the global climate

during this period apparently including tropical latitudes Evidence for

this cooling includes that collected by Savin et al (1975) and Shackleton

(1978) the paleobotanical data evaluated by Wolfe (1978 1980) and Buchardtts

(1978) results from the North Sea region (Figure 7) If indeed SST values

ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o

Figure 7 Long-term trend of SST in the North SEA area isotopically der5_ved from mollusk shells (Ruchardt 1978) Shadowed uncertaJntv due to data sc~ttcr Vertical scale paleotemperatures assuming no ice at continents (before about 40 Ma) and present temperatures after shiFt in oxvgen isotope ~omposition with present ice volume

35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull

22 ~ near 20 0 e (or even lower) had been representative of equatorial and tropical bulllatitudes interpreting them in terms of a global heat and radiation budget

would be a difficult task many of the temperature estimates for this period

are below actual data bull The second feature supported by all available data was the existence of

an ice-free Arctic Ocean More than that temperatures during the Oligocene bull and the whole Miocene epochs (until about 5 Ma ago) must be compatible with a

rich forest vegetation along the Arctic coasts A few examples should be bullquoted here Wolfe and Leopold (1967) report a well-mixed flora of the

broad-leaved deciduous forest type (with more conifers in the uplands) from

southern and central Alaska similar to the contemporaneous forests of Europe

Oregon and eastern Asia (42-55degN) Similar mixed forests are reported from

~stern Siberia (Lena Basin) Wolfe (1980) reports also from a site in eastern

Siberia at lat 70 0 N a well-mixed coniferous forest the annual mean temperashy

ture was estimated to be 3-S o e with an annual mean range of 30-32dege (July

about 18degC) The most impressive vegetation type a rich coniferous forest

is reported from Banks Island in the Canadian Archipelago (lat 74degN) All bullavailable data from Arctic or subarctic latitudes indicate a temperate climate

with summer temperatures well above 10-13degC which is incompatible with a bullseasonally freezing Arctic Ocean

33 The Mid-Miocene Cooling Event

Ocean core data have indicated some rather dramatic changes during the midshy

Viocene (16-12 Ma ago with some variance in the dating quoced) The most

~portant evidence indicates that a major probably complete ice sheet covered bullall of East Antarctica 14-12 Ma ago (Kennett 1977 1980) increased iceshy

rafting and a further sudden drop of bottom water temperatures (Savin et bullal 1975 Kennett 1977) and of SST (Figure 5) In a DSDP core (lat 05degS

long l586degE) with a high sedimentation rate Woodruff et al (1981) found

evidence for a series of repeated cooling events interpreted as fluctuations bull of a growing Antarctic ice sheet between 148 and 140 Ma ago This event

was probably correlated with the first production of cold bottom water in the bull North Atlantic (observed in a core at S7degN Blanc et al 1980) and with a

dramatic increase of diatom productivity in the northern (subarctic) Pacific bullabout 11 Ma ago (Berggren and Hollister 1977) Shackleton (1978) reviewed bullbull

23

the oceanographic evidence for cool temperatures especially in the tropics

Wolfe (1978) reported such cool-climate taxa as alder and spruce from Borneo

and similar data from Puerto Rico and Veracruz Mexico The climatic conseshy

quences of cool temperatures were less pronounced in the southern land areas

the first grasslands appeared in the Murray Basin of Australia and in New

Zealand (Kemp 1978 Mildenhall 1980) and gradually spread northward In

northern continents and shelf seas the temperature drop was much weaker

(Buchardt 1978 Wolfe 1978) But Wolfe (1980) indicates that northeastern

Siberia Alaska and presumably all of northern Canada were dominated by a

rich and diversified micro thermal (boreal) coniferous forest this seems to

indicate that the Arctic Ocean was still ice-free

Kennett et a1 (1977) found evidence of a marked episode of volcanic

~plosions around the Pacific area between 16 and 14 Ma ago (see also Bray

1979 who suggests a close coincidence between increasing volcanic activity

and glacial events) Fourteen of 16 temperature estimates indicated a decline

during this epoch With reference to OKeefes hypothesis (see section 31)

an extraterrestrial object hit the earth about 147 Ma ago--the evidence is

the Ries crater in southern Germany (David 1969) with a comparatively minor

field of tektites The total mass has been estimated to be only 3000 tons

(OKeefe 1976)

After the final formation of the Antarctic ice cap the first local

mountain glaciers in Alaska appeared about 9 Ma ago (Denton and Armstrong

1969) Evidence that the first cold-water fauna existed simultaneously has

been obtained in northern Japan (Kanno and Masuda 1978) In his review of

~ history of African vegetation Maley (1980) indicated a marked climatic

asymmetry in this time period the southern Sahara covered with a tropical

humid (or semihumid) forest while southern Africa and the Zaire Basin were

dry sometimes even fully desertic

34 The Messinian Peak of the Antarctic Glaciation and Its Consequences

In the last subperiod of the Miocene the Messinian (6-5 Ma ago) the

Antarctic ice sheet reached its greatest volume estimated to be about 50

percent greater than at present The ice sheet expanded horizontally up to

the margin of the continental shelf and covered the former mountainous archipelago

of West Antarctica (Kennett 1977) One of the physical reasons for this

bull bull bull bull

24

growth may b~ found in a transition from a warm glacier with temperatures

~ear OdegC and rather fast motion to a cold glacier with temperatures well

below ooe extremely slow motions and a slightly positive mass budget until

a higher equilibrium level is reached (Under present conditions the mass

budget most probably is also weakly positive) The higher level of the Antarctic

ice sheet is also evidenced by the glacial erosion traces on many mountains

well above the glaciers present altitude

This peak is correlated (Kennett 1977 1980 Frakes 1978) with a

general global cooling an expansion of cold Antarctic surface water about 300

km towards north an intensification of the baroclinic Antarctic convergence

in the ocean (also Berggren and Hollister 1977) and a major increase of

oceanic upwelling biological productivity and ice-rafting Bray (1979) also

found a moderate peak of volcanic activity between 64 and 50 Ma ago which

~ay be correlated with global cooling and increased glaciation

The most important consequence however was an eustatic lowering of the

sea level by about 40 m which was due to the storage of water in the huge

Antarctic ice sheet (average thickness then near 2500 m) This drop in sea

level isolated the Mediterranean Sea from the Atlantic Ocean both entrances

north and south of what is now the Strait of Gibraltar were closed Since the

Mediterranean--originally a p~rt of the circumequatorial Tethys Sea which had

been closed also in the east after the collision of the African and the Eurasian

plates about 18 Ma ago (Berggren and Hollister 1977 Hsil et al 1977)--had a

negative hydrological balance (as now) it gradually evaporated and desiccated

to a chain of lakes filled with high-density brine (like the Dead Sea) This

process was repeated 7-10 times creating evaporite sediments (salts and 6 3 ypsum) wit h a thickness up to 300-500 m and a total volume near 10 km

Deep canyons of rivers like Nile Rhone and Durance and even the deep lakes

of the southern Alps formed Further evidence of late Miocene eustatic seashy

level changes has been reported by Adams et al (1977) However Matthews et

al (1980) warn that isotopic data for paleoceanographic reconstructions must

be interpreted carefully

Increasing evidence points to repeated glacio-eustatic sea-level fluctuashy

tions of the same kind as during the Pleistocene The data include the laminashy

tion of the Mediterranean salt layers mentioned above and also a cyclic

carbonate sedimentation in the equatorial Pacific (Saito et al 1975) ~hich

bullbullbullbull (I bullbullbull II II II II

~

I i

25

indicates strong upwelling of nutrient-rich cool water Here 7-10 cyclic

temperature changes were observed with minima as cold as in the cold phases

of the last glaciations These low temperatures should not be taken as indicative

of global cooling but only of a higher intensity of equatorial upwelling

Such cyclic sea-level fluctuations have also been observed just before

the Messinian salinity crisis (McKenzie et al 1979) Apparently the fluctuashy

tions depended upon the waxing and waning of the Antarctic ice sheet The

authors observed approximately 34 cycles of change between fine-laminated

diatomites and dolomitic clays in southern Sicily their time scale has been

estimated to be near 20 ka when the high-water periods (as the Pleistocene

interglacials) were definltely shorter than the low-water periods This

~vidence has also been taken as an indicator of the active role of the Antshy

rctic ice sheet in the evolution of the Messinian salinity crisis

The abrupt onset of the Mediterranean shrinking was thus initiated by a

worldwide event not by the slow evolution of local climate The existing

aridity was only accentuated it extended even into southern and southeastern

Central Europe The final stage of isolated brackish lakes in a slightly

more humid climate (Lago Mare after Hsil et a1 1977) included several

lakes in southeastern Europe (eg in Hungary and the Vienna Basin) where

evaporites were formed as now about 1800 km farther south in the chotts of

Tunisia and Algeria Pollen data expressed quantitatively as a steppe index

(or the ratio of pollen from steppe flora to the total amount of pollen)

indicate that the pollen influx into the Black Sea (Hsll and Giovanoli 1980)

and probably including river sediments was dominated before and during the

-rlinity event by forest pollen only afterwards during the Pliocene did the

percentage of steppe pollen increase from 15 percent (late Miocene) through

25 percent (Messinian) to 35-50 percent

At the same time the conditions near the Arctic had not changed (see

section 33) Hopkins et al (1971) described a flora dated 57 Ma ago from

lat 66degN on the western coast of Alaska as a rich diversified coniferous

forest with hemlock fir larch and even hazelnut and with a low percentage

of grass and herbs at a site which is now tundra The insects of this deposit

are comparable to those now living in British Columbia between lat 48 and

54QN

It is a remarkable fact that--according to the available evidence--the

peak of the Antarctic glaciation during the Messinian about 6 Ma ago was not

I

bullbull

mrs

26 bull

accompanied by a significant cooling of the Arctic As we shall see (section 35) bullconvincing evidence for a large-scale glaciation of the northern continents

and for a (at first seasonal) ice cover at the Arctic Ocean is not available

until 35 Ma ago during the mid-Pliocene It is this period of early and bull middle Pliocene (5-35 Ma ago) that shows the highest degree of climatic

asymmetry and is of highest interest for any applications to a scenario of bull future conditions During and after this relatively recent period continental

dr1ft is only of minor importance mountain building has (at least) started bullthus the boundary conditions are--while not identical--more comparable to the

actual pattern than at any time before A careful comparative investigation bullof the climatic conditions based on all available floral and faunal evidence ~frm all continents and the rich paleoceanographic data should certainly

i~rove our understanding of this strange climatic asymmetry and can serve as

background for more sophisticated climate modeling bull 35 Evolution of the Arctic Drift Ice and Contemporaneous Climatic bull

Events bullThe early evolution of the Northern Hemisphere glaciation as intimately

connected with the evolution of the Arctic sea ice has been best described in

a deep-sea piston core from the western equatorial Pacific (46degN l396degW) bull (Shackleton and Opdyke 1977) Since piston cores reaching down well into the

Pliocene can only have a very small sedimentation rate (here about 6 mm per

~usand years) the bioturbation from burrowing benthic animals prohibits any

investigation with a high time resolution Thus a loss of detailed informashy bulltion is necessarily correlated with the gain of a much longer time scale here

up to 35 Ma (ie within the Gauss subchron of the paleomagnetic time

scale) In the lowest layer before 32 Ma ago the ocean was in an intershy

glacial stage with only weak variability of its isotopic condition (see 18

bullbullFigure 8) If the observed variations in the levels of 0 0 were entirely due

to real variability glacial events could not have caused eustatic sea-level

fluctuations of more than 26 m This could be caused by changes in the Antarctic

ice sheet or by small Northern Hemisphere glaciations (about 25 percent of the

volume of the last maximum 18 ka ago) or possibly only by analytical error bullJust below the onset of the Mammoth paleomagnet ic event about 33 Ma ago bullbull

27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)

~hln R TimC series of jlRO as representing global jce volurrte during the lnRt 15 Mn (Shackleton and Opdyke 1977) Paleomagnetic time scale at hottnm (11-1R MD ago) not linear wi~h core depth (above) Note beRinninp pf stHlng fluctuations stnre the early rauss subchron (33-29 ~fa ago)

bull

larger excursions in isotopic composition are observed well above analytical

uncertainty representing about a 40 m sea-level equivalent this date is in

substantial agreement with the first appearance of ice-rafted grains in DSDP

cores and with the earliest evidence of glaciation in northeastern Iceland

(Einarsson et a1 1967) Fluctuations of this size dominated the whole Gallss

subchron (33-24 Ma ago) while from the beginning of the Matuyama subchron

on (since 24 Ma) there were isotopic excursions equivalent to sea-level

fluctuations of 60-70 m or two-thirds that of the late Pleistocene (since 07

~a) Evidently a major change in the character of glaciations occurred about

25 Ma ago probably together with a large drop in the continental biomass as

evidenced by a parallel series of 13C data (Shackleton and Opdyke 1977)

In the last five years several other investigators have found evidence

that during this period between 35 and 25 Ma ago many other datable climatic

(or climatogenic) events occurred which fit rather closely together The

most important seemS to be the gradual blockage of the great North Equatorial

Current then between West Africa and Indonesia by the uplift of the Isthmus

of Panama about 35 Ma ago (Saito 1976 Berggren and Hollister 1977

Keigwin 1978) This current had persisted since the Jurassic (about 150 Ma

ago) the rising isthmus increasingly blocked its Atlantic part and deflected

it northwards thus contributing to a much more vigorous Gulf Stream Paleshy

bullbullbull

bull oqanographic lvidencC presented by Keigwin (1978) is complemented by paleoshy

zoological evidence that is the onset of migration of land mammals between bullthe two Americas after their merger about 3 Ma ago (Webb 1976) This evolution

of the land bridge and the consequent change in ocean currents led to increased bullheat and water vapor input into the atmosphere in the critical region along

the eastern coast of North America and the Labrador-Greenland-Iceland area bullSince all traces of earlier glaciation have been removed from Greenland and

th~ LabradorHudson Bay area by the multitude of Pleistocene glaciations only

the s~quenc~ of 10 glaciations in Iceland suggests the early onset of the bull northern glaciation evidenced by the oceanic cores

Independently Herman and Hopkins (1980) interpreted the evolution of bull the Arctic Ocean climate from a dozen deep-sea cores obtained from ice platforms d~ting over the central part of the Arctic basin in a sequence of three time

units The oldest unit (III) comprises the period 45-25 Ma ago when the

Arctic deep-sea bottom consisted of red clays with manganese micronodules

(indicating high bio logical productivity) but also included a few planktoni c

foraminifera like those now living in polar seas and a small amount of iceshy bullrafted sand grains The top of this unit is paleomagnetically dated just

below the Gauss-Matuyama boundary it is characterized by rather low SST

(comparable to that of the Pleistocene interglacials) and also by the absence bull of a well-defined density stratification (ie by strong vertical mixing and

oxidation of bottom sediments) These characteristics exclude perennial sea bull ice but would be compatible with seasonal sea ice probably similar to the

present situation in the subantarctic ocean

The base of unit II just below the Matuyama (24 Ma ago) represents a

hrior oceanographic and climatic threshold with the lack of manganese bullmicronodules and the color change from red into tan indicating lessened biological

productivity and weaker vertical mixing The inception of a strong salinityshy

density stratification in the Arctic has been interpreted as a consequence of bull the dilution of surface water by the influx of large quantities of fresl]

glacial meltwater and thawing icebergs during early deglaciations of Arctic bull lutitudes SST us indicated by planktonic foraminiferal fauna seems to be

incolllpntible with the presence of perennial ice hut a seasonal icc cover may bull have been present and woulJ have enhanced the salinity stratification by a

number of related processes during melting and refreezing For further details bullincluding the evolution of a (more or less) permanent sea ice cover during the

2Y

last 07 Ma see also Herman and Worsley (1980) and with some differences

Margolis and Herman (1980)

Further evidence for this development has been given by Gradstein and

Srivastava (1980) who found along the shores of Labrador a termination of

the influx of warm Gulf Stream water and its replacement by cold low-salinity

water from the north thus indicating the full establishment of a cold Labrador

current in tile middle to late Pliocene In contrast the absence of tundra

along the Arctic shores during and before the mid-Pliocene (see Frenzel 1968

and section 34) indicates that until 35 Ma ago SST was probably higher than

now Here comparative paleobotanical and paleoceanographical investigations

are needed

- The evolution of Northern Hemisphere glaciations and of Arctic sea ice

between 35 and 25 Ma ago is also reflected in corresponding climatic data

from quite different latitudes here only a selection can be given without

further details The first widespread glaciation in the Patagonian Andes

occurred about 35 ~m ago (Mercer as quoted by Kennett 1980) Keller (1979)

observed a strong cold event in a core within the Kuroshio Current 32 Ma

ago A deep core from fossil Searles Lake in interior California (Liddicoat

et al 1980) demonstrated the first formation of a perennial lake in a

hitherto arid environment during the Mammoth paleomagnetic event 32 Ma ago

In the Siwalik Hills of northern Pakistan a strong faunal change occurred 247

Ma ago (Opdyke et al 1979 without any paleoclimatic details) definitely

hefore the uplift of the Himalayas which is evidenced by conglomerates just

p)r to the Olduvai paleomagnetic event (18 Ma ago) Sahni and Mitra

(~80) found in northern and central India (except northeast and southwest

India) the beginning of an arid (or more probably semiarid) period at the end

of the Pliocene with growing continentality due to the rise of the Himalayas

estimated then to have attained an altitude of 1000-1500 m Bsli and Giovanoli

(1980) evaluated from fossil pollen influx at the bottom of the Black Sea a

(time-averaged) steppe index which rose from about 20 percent during the

Messinian (section 34) to about 50 percent at 35 Ma ago and to 70 percent and

more at 25 Ma ago Along the New Zealand coast Mildenhall (1980) observed a

more arid climate after the mid-Pliocene

[n tropical latitudes (mainly 0-20 0 N) the monsoon circulation--a lowshy

tropospheric monsoon flow from west or southwest and an upper tropical

easterly jet at 400-100 mb--dominated the climate during summer above the

bull cont~nental section of the Northern Hemisphere between West Africa and the

Philippines Since its intensity depended largely on the elevation of the

Tibetan Plateau (Flobn 1964 1968) the intensification of Himalayan uplift

jllst prior to the Olduvai paleomagnetic event (see Opdyke et aI 1979) also

cauRed marked changes in other areas of this circulation the distinct increase

of rainfall at Lake Turkana in northern Kenya (Cerling et al 1977 Cerling

1979) should bementioned

[t would be premature to derive from these scattered data an internally

ronsistent picture of the evolution of the present climate--to be more precise

of its interglacial mode--during that period of the late Pliocene It Is

sobering to see that our present climate mode characterizes only about 10-15

per0~nt of the (geologically) short time span of the last 3 Ma ~lich is less

th~O1 percent of the age of the earth Obviously paleogeographic and

tectonic events such as the closure of the Isthmus of Panama and (for limited

periods) the Strait of Gibraltar and the uplift of the huge Himalayas and

many other climate-shaping mountains have played an important if not overshy

whelming role in the evolution of our present climate Similarly important

were the formation of a powerful ocean current that encircled the Antarctic

continent at high latitudes thermally isolating it and the formation of the

Arctir see ice with its climatic consequences apread over the whole globe~

From this evidence it must be concluded that the large-scale evolution of

both polar ice caps occurred completely independently at quite different

times If this is the case then the factors usually accused of global climato- 4t genesis--such as possible variations in the solar constant or in the composhy

s1-n of the atmosphere--play only a secondary role in climatic evolution

dur ing the las t 40-50 Ma Thus we should bear in mind tha t the bounda ry

conditions of the climatic system at the earths surface with their paleoshy

geographic changes obviously have been more powerfulin the paleohistory of

our climate than any external influences

Models are (or promise to be) powerful tools in interpreting existing

climates Even their most comprehensive examples necessarily contain simplifishy

cati)fls sometimes oversimplifications Sjnce nature alone is able to solve

the completl set of equations determining climate under given boundary condishy

tions the history of its evolution is an at least equally useful key to

climate Consequently we should cautiously dig to assemble and to understand

It

that history Until a more complete evaluation of the existing sources has

been made only a first-order scenario can be derived from available incomplete

data (Chapter 5)

CHAPTER 4

CRITICAL THRESHOLDS AND TIME SCALES OF POSSIBLE

MAJOR CLIMATIC EVENTS

In recent considerations of the possible climatic consequences of any

future CO -induced global warming (see eg Hughes at al 1980 Kutzbach2and Webb 1980 or Flohn 1980) two major climatic events were mentioned as

possible key issues

Event A A disintegration of the marine-based part of the West

Antarctic ice sheet causing a 5-7 m rise of the worlds sea level

Event B A disappearance of the perennial drifting sea ice in the

Arctic Ocean associated with a substantial increase of its sea surface

temperature and with a major shift of climatic belts

The possibility of a future total collapse of the Antarctic ice sheet was

first mentioned by A T Wilson (1964) His basic idea was a melting of the

bottom of the ice a condition verified by observations in West Antarctica

(fow et )1 1968) but not by those in East Antarctica where only minute

pockets of meltwater exist on the bottom The present state of this discussion

has been outlined in DOE Workshop 009 (Hughes et al 1980)

M I Budyko (1962) first suggested the possibility of a total disappearance

of the Arctic sea ice He (1969 1977) and others also suggested the possible

relation of this disappearance to CO -induced warming The paleoclimatic2

-history (Chapter J) indicates that during at least 10-12 Ma--between the midshy

Miocene and the late Pliocene--an ice-free Arctic Ocean existed simultaneously

~ith ) fully glaciated Antarctic continent The extent to which the Arctic

Ocean became perennially ice-free during some periods of the Matuyama subchron

(24-07 -fa ago Herman and Hopkins 1980) remains unknown

A collapse and partial disintegration of the West Antarctic ice sheet

occurred most probably during the last interglacial the Eem (about 125 ka

ago) Evidence for that event has been reported by Hollin (1980) and Aharon

et a1 (1980) A core from the southern Indian Ocean offers further convincing

evidence (Dansgaard and Duplessy in press) Isotopic datA from henthic foraminishy

fera in the core indicated a low global ice volume (stage 5e = Eem) for a long

period In the middle part of the period probably 5-6 ka before its end

t III

isotopic data from planktonic foraminifera indicate a sudden marked drop in

SST similar to the data from New Guinea (Aharon et al 1980) A further

even larger drop in SST has been suggested in a later part of stage 5 about

95 ka ago by Hollin (1980) However new data from the stable Bermuda

platform (Harmon et al 1981) are incompatible with this hypothesis but are

consistent with the 125 ka-event and a 4-6 m rise in sea level The West

Antarctic ice slleet is probably much younger (only 6 Ma) than that of East

Antarctica (section 34) While disintegration of the West Antarctic ice

(Event A) last happened only 125 ka ago the last unequivocal occurrence of

an ice-free Arctic Ocean (Event B) was much earlier (24 Ha ago)

Using the model-dependent equivalence (see the appendix) between CO conshy2

centration and representative surface temperature as a reasonable approximashy

t i~ (Flohn 1978b t-1unn and Machta 1979) researchers have employed charactershy

istic warm paleoclimates as first-order scenarios for future climatic stages

that would be expected during a CO -induced warming This relation has indeed2 bull

been strengthened by the recent discovery that CO levels in Antarctic and2

Greenland ice cores have varied between about 200 ppm (last glaciation 18 ka bullago) and 350-400 ppm (Holocene warm phase about 6 ka ago) (Delmas et al 1980

Oeschger 1980) Using the time sequence of paleoclimatic events as a first bullguide into forthcoming events one could indeed assume that Event A with

its last occurrence 125 ka ago could arrive earlier than Event B with its

last occurrence probably 24 Ma ago However there are some considerations bull which suggest that in fact Event B may occur first

bullbull i

According to the equivalence between CO levels and representative surface2

terr~rature Event A has been associated with a CO concentration of 500-610 ppm2

an~vent B with a CO level of 630-850 ppm (cf Flohn 1980 p viii) For2

bullbullconvenience we may choose 550 (plusmn10 percent) and 750 (plusmn16 percent) ppm as

thresholds for a revision of these values see the appendix

However because Event A requires a preparation time with the earth at

elevated temperatures that is much longer than the time to prepare for Event H

the time sequence of the occurrence of the events may be reversed Critical bull prenqlliHites of Event A have been given by Mercer (1978) lie suggests that tile

nbsenu of drifting ice together with an SST rise in the vicinity of Antarctica bull Thi8 sequence of data is also at variance with a widely quoted speculation

of a triggering of Northern Hemisphere glaciations by an Antarctic ice bullsurge (Flohn 1974) at least for that well-documented case bullbull

J)

of ahout )0r would be necessary to initiate a disintegration of the marine-

based part of the West Antarctic ice It must be mentioned however that

part of his evidence has recently been challenged by Sugden and Clapperton

(1980) TIley conclude that in the Alexander Island section of the Antarctic

Peninsula (lat 70-72degS) no sign of progressive ice sheet collapse can be

found rather there seems to have been a local expansion of the ice shelf

However their argument seems to be insufficient to discard Mercers hypothesis

completely

The possible time scale of Event A is rather uncertain Hughes et al

(1980) distinguished between a slow mode and a fast mode of the disintegration

of a marine-based ice sheet In slow-mode disintegration the velocity of ice

streams exceeds the calving rate of icebergs at the front so that floating

~ce shelves form and spread This mode is favored when the floating part

remains pinned by islands or shoals as is the case with present Ross and

Filchner-Ronne ice shelves In the hypothetical fast-mode disintegration

iceberg calving rate would exceed the speed of ice streams leading to a

formation of calving bays migrating up the ice streams and carving away the

marine ice domes Hughes et al suggest that perhaps Pine Island Bay (near

long 1100W) may form such an example if there are no high bedrock sills

beneath the adjacent glaciers In a careful geophysical survey Jankowski and

Drewry (1981) found no high bedrock sill at Thwaites Glacier one of the two

glaciers calving into this bay From the other the Pine Island Glacier

bull no evidence is yet available

Fast-mode disintegration may have marked the decay of the last glaciation

~1 the Hudson Bay area (cf Hughes 1977) Here evidence has been found

(Andrews et al 1972) for a catastrophic incursion of the sea about 7800

years ago as determined by radiocarbon techniques and lasting not more than

200 years between the northern inlet and the southern tip over a distance o[

about 1200 km Simultaneously an equivalent sea-level rise was observed on

the opposite side of the Atlantic by 7 m (during about 200 years) on the

coasts of western England near Liverpool (Tooley 1974) and by 10 m on the

western coast of Sweden (Morner 1976) While the first figure appears to be

representative the latter may be somewhat exaggerated by local isostatic

uplift Another even larger surge of this type may have happened some

millennia before in the area of the Baltic (Gulf of Bothnia) on a comparable

time scale (Hughes et al bull 1977) but no detailed investigations are available

lh

Front this admi t tedly incomplete and somewhat con troversial evidence it

should be concluded that even for the fast-mode disintegration of a marine

ice sheet a time scale on the order of a few centuries may be needed once

the prerequisites are established Mercers estimate of a (local) SST rise of

+S degc may s till be reasonable and could be taken as representative within our

context Along the Antarctic coast the ice-albedo-temperature feedback is

much weaker than in the Arctic (Manabe and Stouffer 1980) mainly because of the

large seasonal variations of sea ice thus the +SoC value could be used in

our evaluation of the required CO concentration However it is definitely2

higher than ollr estimate for the Eem interglacial (AT = 2-25 degC) Under

natural conditions (cf the case studied by Dansgaard and Duplessy in pressa by Aharon et aI 1981) a warm Eem climate lasted for several thousand years

before Event A occurred These investigations seem to indicate that the

longer time scale is much more likely than the rapid occurrence quoted by

Mercer (1978) Another important reason for this preference is the existing low

temperature within the Antarctic ice far below the regelation level which

makes fast-mode disintegration unlikely in the near future

Let us now turn to the case of the Arctic sea ice Two and a half million

years ago before the formation of this ice (as estimated from the evidence of

local Pliocene vegetation) the representative temperatures in middle and high

latitudes must have been about 4-SoC higher than they are now This difference

coincides rather well with a figure of OT = +4degC given by Budyko (1977) Taking

into account the probability of a lag between the change in sea surface temperashy

ture and the formation or vanishing of sea ice we may better determine the

Ie of the dest ruct ion of the sea ice by making est irnates based on the higher

value of 5degC The geophysical processes controlling the seasonal melting and

refreezing of the sea ice have been modeled by Maykut and Untersteiner (1971)

using data observed during the International Geophysical Year 1957-58 Disshy

regarding details given by more recent investigations we may summarize the

fundamental result as follows the average equilibrium thickness of the

(broken) perennial sea ice cover is 3-4 m the annual melting from above

during the 70-day melting period and the refreezing from below are eacll under

equilibrium conditions about 50 cm per year Model experiments indicate that

these processes are particularly sensitive to changes of the surface albedo

(as controlled by the snow cover at the surface of the ice floes) and to the

heat flux from the ocean (ie to changes of SST) Assuming a 10 percent

37

change for example in the length of the melting season we can easily see

that such a minor change could lead to a final disappearance of the sea ice

during the course of a few years For example annual melting of 55 cm per

year and refreezing of 45 cm from below net a 10 cm loss per year At this

rate a 3-4 m thickness of ice disappears in 30-40 years It is not possible

here to enter into more details which include also some (positive or negative)

feedback mechanisms especially in the case of thin ice But the conclusion

that this multiphase system is highly sensitive to minor changes in geophysical

parameters remains valid Thus the possibility of a very fast response of

the sea ice to a CO -induced global warming ~n a time scale of a few decades2

or Less) must be considered This possibility agrees with the results from

~udYkos simple energy-balance model (1969 1977)

If as expected CO -warming increases during coming decades the sea2

surface temperatures will also be affected after a delay of 10-20 years

(Hoffert et al 1980 and other authors) Indeed SST is the key geophysical

parameter controlling both Events A and B During the course of global warming

the extent of seasonal ice will be reduced graduallY in the Arctic but less

so around the Antarctic because here the cold katabatic (down-slope) winds

seasonally produce a large amount of sea ice The strong baroclinic circumshy

Antarctic current should also prevent an early warming of the ocean near the

ice shelves Most probably the changes leading to Event B will proceed much

farther than those for Event A during the expected evolution of warming

bull The preparation of Event A probably takes a much longer time perhaps even in

the order of millennia Nevertheless since Event A will have such serious

~onseqllences great research efforts into its largely unknown geophysical

background are indeed indispensable

Both events may be expected to have most serious and indeed catastrophic

consequences for the worlds economy and human welfare The risk of Event A

is a sea-level rise of 5-7 m For Event B the risk is a significant change in

climate a d~scription of which will be attempted in Chapter 5 The risk of

both events increases sharply as the CO concentration approaches 750 ppm 2

Error bands on this estimate are broad perhaps + 16 percent (also see appendix)

But since Event A needs a longer perhaps much longer preparation time than

Event B one should expect the latter event first

CHAPTER 5

TOWARDS A CLIMATIC SCENARIO OF AN ICE-FREE ARCTIC

In formulating a scenario for a possible climate of an ice-free Arctic

two caveats should be heeded First paleoclimatic data--including those from

the early and mid-Pliocene (5-3 Ma ago)--cannot be used uncritically Two

major paleogeographic changes occurred at (or after) this time (see Chapter 3)

(1) the closure of the Isthmus of Panama with a subsequent intensification of

~ the Gulf Stream system and consequently the North Atlantic subtropical gyre

and (2) the final uplift of the Himalayan system from altitudes near 1-15 km

to at least 4-5 km (rolling surface of the Tibetan plateau) now The latter

event was probably simultaneous with the uplift of other mountains such as

the Alps (The Rocky Mountains of America may have been uplifted before the

Pliocene) Model studies (Hahn and Manabe 1975) have demonstrated that the

present monsoon circulation--consisting of westerly and southwesterly winds in

the lower troposphere together with a tropical easterly jet both extending

during northern summer between West Africa and the Philippines (20 0W-1400E)-shy

is largely a result of the mountain pattern Thus this circulation system could

bull have existed only in a rudimentary form during our comparison epoch and data

from that time cannot be used as representing a near-future climate with CO2 shy

induced warming without a correction for the present land-sea-mountain pattern

The second caveat deals with the lack of an adequate general circulation

model describing this type of a fully asymmetric unipolar glaciated climate ~ early experiments reported by Fletcher et a1 (1973) give hardly more than a

few hints Using a few semiquantitative estimates of circulation parameters

we can outline the broad atmospheric (and oceanic) circulation patterns to be

expected Climatological experience may be used--not as a handwaving experiment

but to suggest some physically reasonable (and internally consistent) latltudeshy

dependent numerical comparisons with the present climate

Since the relationship between the meridional temperature difference (I)

and the latitude of the subtropical anticyclonic belt (centSTA) ought to b~

considered as representing planetary conditions we may use this relationship

(Figure 2) to estimate the latitudinal changes of climatic belts caused by a

global warming intensified in Arctic and subarctic latitudes by a snowiceshy

albedo-temperature feedback If T increases especially in high latitudess

40

r will decrease A reasonable estimate (Chapter 4) of the expected changes

(6) can be obtained with

tlf -kAT s

where the amplification factor k can be derived using latitude-dependent Ts

data from Manabe and Wetheralds (1975 1980) CO2-temperature model (see

Cates 1980 and Washington and Ramanathan 1980) The negative sign indicates

that with increasing global temperature the meridional gradient decreases as

mentioned before (Flohn 1964 Frakes 1979)

A representative relationship between r and $~TA has been derived (Figure 1)

from actual data Correlations between these prtrameters indfciHed the highest

valf (091-092) (Korff and Flohn 1969) when 1gtSTA lags one to two months behind

r ~lile temperature data usually lag about three to four weeks behjne the

seasonal cycle of the suns declination and zenith angle Figure 1 gives a good

example of such a lag of two to three months of the shift of climatic bel ts (the

intertropical convergence zone at the central Atlantic Ocean) Therefore

any estimates of monthly or seasonal values of ~STA directly from r leads to

systematic errors ~ - ~ b is usually about 1-15deg lat (Table 4) Formiddotest 0 s

our comparison we use unly the estimated values an approach justified by the

unavoidable observational errors (especially in interpolating ~STA from latitushy

dinally averaged pressure data) and the high correlation between simultaneous

pairs (Chapter 2) During northern summer the larger errors in observed iflSTA

data are caused by low pressure values above the continents (ie monsoonal

lo~entered near 30 0 N)

In order to use the relation between r and ~STA we must estimate the

temperature of the 700-300 mb layer above an ice-free Arctic If one could

use the paleoclimatically estimated changes of surface temperature for that

layer the estimation would be easy This process would lead to rather low

and unlikely figures for two (interrelated) reasons (1) Present temperatures

above on ice-covered Arctic Ocean are controlled by a nearly permanent surface

inversion (during all seasons) which should be absent above an ice-free

Arctic certainly during the cold season when surface winds from the (probably

snow-covered) continents north of the Arctic Circle are converging over the

warm sea resulting in an unstable atmosphere near convective equilibrium

(2) A large-scale ice-albedo-temperature feedback would be lacking above an

Table 4 Ob~Jlved and Estimated Values of r and ~tA

during Extreme Seasons (Northern Hemisphere)

bullbull

42

ic~-free sea even though the feedback is maintained but weakened above the

subarctic continents during winter

A reasonable assumption can be derived from the above-mentioned relation

tr = -kbT The amplification factor k can be estimated by using the latitudeshys

dependent increase of tTs derived from the 2xC0 and 4xC0 models given by2 2

Manabe and Wetherald (1980) These models do not include the ice-free Arctic

but are indicative of temperature distribution with a general global warming

Frum the results of the models we estimate that the tropospheric temperature

above the ice-free Arctic rises by a factor k = 14 more than the averagp sur[~c~

temperature increases This could be a minimum estimate since it disregards

the complete disappearance of the surface inversion and the additional rise of t~ospheric temperatures above an ice-free Arctic Ocean with an annual surface

temperature around +SoC If we take this into account the parameter k = 14

may rise to a value somewhere between 1 5 and 1 7 Because the typical height

(pressure) of the surface inversion varies between 1 and 2 km (900 and 800 mb)

the effective tropospheric temperature (eg of the 1000-300 mb layer) is 150

affected by temperature changes below 850 mb only to 700(~ 21 percent) As an

upper value we may choose an amplification factor of k = 17 for the annual

value Another important factor to be taken into account is the seasonal

variation During summer r is now about 07 of the annual value (July

0665) during the long polar winter about 12 (January 1219) After the

melting of the sea ice and the consequent effect on the heat budget the

seasonal differences may increase we may assume here (subject to modification) 1 a preliminary value of 05 for summer and 15 for winter conditions The

a~jmed changes of r are given in Table 5

Using these values for flr in the regression line of Figure 1 we obtain

estimates for ltfJ (Table 5) The expected changes of the latitude of STASTA are during summer +18 to 29deg during winter +36 to 60deg and for the year bull+30 to 45deg The annual data are of course more trustworthy than the

seasonal ones The calculated values for winter resemble the present data for

October or November for summer no comparison is possible but the shift of

STA is probably limited to 200-300 km bullIn a 1980 paper the author proposed (p 65) only 100-200 km for summer

but about 800 km for winter The present estimate uses more quantitative but

modifiable relations smoothing the seasonal differences Larger seasonal

differences were suggested mainly by the high seasonal variation of expected bull

~l

Table 5 Estimated Changes of r under Different Assumptions

and Resulting Latitudes of Subtropical Anticyclones

ltgtSTA(Olat)Surface Amplification Change in r Warming Factor Year Winter Summer Year Winter Summer

+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(

Present Climate (for comparison) 360 337 403

44

temperature changes n~ar the surface in a permanently ice-free Arctic Ocean ~

like that of 24 Ma ago In this case the summer SST and air temperature bullprobably had risen from the ODC (current value) to SOor even 10DC This rise

is confirmed by the paleobotanical evidence of rich coniferous forests at high

latitudes such as Banks Island (74degN) at the outer edge of the Canadian Archishy

pelago indicating air temperatures of l2-l3degC or more During winter SST and bullair temperature could not have been lower than freezing (about _2degC) if a

seasonal ice cover did not exist (except in coastal regions) This temperature

WilH ill marked contras t to present values of air temperature around -34 DC bull while SST below the ice cover remains at -2degC due to the high heat storage

capacity of the ocean and the insulating properties of even a thin broken bullsea-ice cover In the case of an open Arctic one should also expect marked bull s~onal variations During the long winter there would be convergence of

cold winds from the snow-covered land high convective instability of air with

high evaporation high frequency of cloudiness and frequent precipitation

reducing radiational loss of heat By contrast during summer with an ice-free

Arctic the subarctic continents should be heated more than today when maximum

temperatures up to 37degC are observed at several stations along the Arctic

Circle the surface winds would diverge from the (relatively cool) sea towards

the surrounding continents thus producing subsidence and low amounts of bullcloudiness and strong input of solar radiation which is stored in the upper

layers of the ocean (For example northernmost Greenland currently receives

an average of 22 hours of sunshine per day in May and JUfle)

Without appropriate mathematical and empirical models the prevailing bullcirculation and weather types at high latitudes in the case of an open Arctic

~ difficult to imagine During winter the air above the ocean would certainly

be warmer than above the continents strong baroclinic gradients along the

coast should favor cyclogenesis with retrograde (E ~ W) eddy motion and mnch

increased snowfall in coastal regions and also in Greenland The fate of the

Greenland ice is somewhat uncertain summer melting would increase at least

in lower altitudes but should hardly surpass a rate of 40-50 cm per year which

would cause an annual sea-level rise of 2-25 mm in addi lion to the present

(unexplained) rise of 12 rom per year However during the greater part of

the year high cyclonic activity would greatly increase the frequency of

precipitation (mostly as snow) this factor of increasing accumulation has not

been taken into account by Ambach (1980) who suggests a sensitive response

I 45

to a CO -induced warming For either process any substantial change in the 2

mass budget will be slow on a time scale of millennia and not of centuries

further studies (cf Dansgaard and Duplessy in press) are recommenderl

The possibility of a surge fl of the West Antarctic ice sheet has been

discussed in Chapter 4 Further changes in the mass budget qf the much greater

East Antarctic ice should occur over a period of time even longer than for

Greenland From the viewpoint of a climatologist its stability for at least

100000 and more probably a million years seems to be secured and also

indicates slow changes of climatic conditions at high and temperate southern

latitudes

By contrast remarkable changes are possible in the Northern Hemisphere

~hey have been included at least partly in the recent model results of

Manabe and Wetherald (1980) and of Manabe and Stouffer (1980) (cf Chapter 6)

As indicated above an important result is the northward displacement of the

(cellular) subtropical belt with atmospheric subsidence and aridity and is

given by the changes in the parameter ~STA This displacement affects the

distribution of rainfall (P) and potential evaporation (E) which are usually

negatively correlated Through P - E ~STA affects the continental freshwater

budget which shows stronger variations At present large oceanic and conshy

tinental areas in the belt 35-45degN (except the areas of quasistationary upper

troughs above eastern Asia and Eastern North America which prohibit the

evolution of subtropical anticyclones) belong to the climatic zone of subtropical

winter rains (cf Figure 9) This zone covers the belt between the extreme

positions of STA during summer and winter winter rains prevail only poleward

)f the STA If as suggested in Table 5 the STA shifts t)orthward about 4-6 0

lat during winter but only 2-3 0 lat during summer the width of the belt

through which STA moves is reduced by about 50 percent This estimate is

considered conservative the reduction may be even more It leads not only to

a reduction and a northward shift of the subtropical winter rainbelt but

also to a shorter duration of the rainy season At the southern fringe of

tJais hell (eg in areas like southern California the Maghreb of North

AfriCA or the southern part of the Near and Middle East) the semiarid winter

rain climate should be replaced by a more arid climate with only occasional

rains in exceptional situations And at the northern fringe of that belt at

average lat 45-50 0 or even more temporary droughts will become much more

frequent especially during the summer

bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

Present IIIt8 T ertiarv

~ 15=humid 2 = semihumid 4 bull semihumid fur] ~~polr ~ 1111111 1 ni val

Figure 9 Generalized patterns of main climatic belts at an idealized continent (center) and adjacent oceans (Flohn 1981) at present and during late Tertiary I = tropical all-year rain-belt 2 = tropical summer rains 1 = arid belt 4 = subtropica1 winter rains 5 = temperate belt without dry season 6 = subpolar zone with seasonal snow and ice 7 = high polar cap with permanent snow and ice Note that now zones 1 and 4 disappear at the eastern side of the continent due to j qlJ3sistnt ionary upper trough late Tertiary hc-re only coniectllred (no date) assum(ng weakening of trough

This same reduction of rainfall necessarily correlatd with higher

potential evaporation and thus with increased aridity is one of the most

remarkable conclusions verified from comprehensive model investigations

Manabe and Wetherald (1980 their Figure 14) obtain a similar shift of the

water budget P-E with a fourfold CO increase The shift is concentrated2 between lat 38deg and 49degN (see Figure 10) with a northward shift of the

marked slope (ie of the northern limit of the arid belt) by 3-4 0 lat

Figure 10 StlggeRtH that at lat ~5degN it fourfold [nercus of CO could be2

correlated wilh a urop of P-E from about 12 mm per day to 05 mm per day

The coincidence between these two estimates obtained with quite different

methods is very satisfying NotWithstanding a worldwide increase in humidity

and therefore of P-E this is a climatic belt in which one must expect increasing

bull bull bullbullbull

bullbullbull bullbullbullbull

47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude

Figure 10 Zonally averaged values of the difference between precipitashy tion and evaporation on land after ~anabe and Wethera1ds (1980) general circulation model with different CO levels Note the stron~ decrease2of P-E (emday) around lat 38-49 DN

aridity These results also coincide with the observeri shift (of lbollt 4deg

lat) of the northern limit of the evaporite belt of the Northern Hemisphere

between the late Tertiary and the present (Lot~e 1964 see Figure 11 after

Flohn 1980) disregarding the anomalies caused by the recent (Plioceneshy

Pleistocene) uplift of many mountains

bullbull

4)

ORAU 81863

bull

-- auaternary - - __ late Tertiary Early Tertiary

Figure 11 Evidence for the displacement of the northern boundary of the Northern Hemisphere arid zone (evaporite sediments) during early Tertiary (50-30 Ma ago) late Tertiary (15-5 Ma ago) and Pleistocene (2-0 Ma ago) compiled by Flohn 19RO using several maps given by Lotze (1964)

One of the most important factors in the future climate evolution is the

~ected shift of the intertropical convergence zone CITCZ responsible for

the position and the seasonal variation of the tropical rain belt Details of

this have been little known Figure 3 gives one of the few available examples

based on a great number of observations with a meridional resolution of 1deg bulllat along long 25degW (central Atlantic) Comparison with the observed

positions of ~STA (Figure 1) at both hemispheres reveals that the ITCZ at this bull(apparently representative) longitude deviates systematically from the midpoint

between the two STA belts The annual average position of the ITCZ at 25degW is

lat 61degN in good agreement with an independent evaluation of the equatorial

surface pressure trough as derived from Pf1ugbei1 s (1967) zonally averaged

data The mid-position between the two hemispheric belts of STAt however is bull only 24degN If one shifts the monthly midpoint between the two STAs north bullbull I

49

by 37 0 lat (61 - 24) (assuming that the well-known greater width and

intensity of the southern trade wind belt are seasonally constant) two deviashy

tions between the first-order estimate of ITeZ so obtained and the position

observed in the central Atlantic are revealed First the seasonal shift of

the observed position in the central Atlantic is greater (106deg lat instead

of 820 lat) second there is a systematic lag of the observed ITeZ position

of nearly one month behind the globally estimated trend probably due to the

usual lag of ocean events caused by its heat storage

If the estimated annual shift of the northern STA were only 4deg lat

northward and the southern STA belt remained at its present position the

resulting northward displacement of the rTez would be 2deg lat or more Such

an evolution would likely be connected with a further weakening of the northern nadley cell while the southern cell remains more or less constant This

suggests a further increase of the asymmetry of the two Hadley cells probably

displacing the rTez an additional 1-2deg lat to the north Thus its average

position should be estimated to be a-lOoN instead of lat 6deg now with zonally

averaged seasonal fluctuations between 4-SoN (northern winter) and 13-l5degN

(northern summer) This would indicate that the southern trades may cross the

equator during the whole year (not only during southern winter) and that the

tropical rainfall belt shifts nearly entirely to the latitude belt 0-200N

together with an extension of the southern semiaridarid climates to the

immediate vicinity of the equator (cf Maleys paleoclimatic results in section

33) Especially such areas as northeast and central Brazil GabonAngola and

the Zaire Basin south of the equator Tanzania and southern Kenya could be

~dversely affected by such prospects The role of upwelling ocean water in

the belt immediately south of the equator will be considered later in this

chapter

However it remains rather doubtful that the expected northward displaceshy

ment of the tropical rainbelt could affect areas like the present SudanSahel

belt of Africa (between lat 10deg and l6-18degN) Here man-made desertification

leading to increasing surface albedo increasing subsidence and decreasing

sni J moisture Rg modeJEri first by Charney (1975 cf also Potter et Rl 19H1)

must he taken into account These processes most probably would counteract

any large-scale shift of the tropical rainfall belt at least as long as it Is

not possible to efficiently control the destruction of newly formed vegetation

by human interference in an area with increasing population stress

50

What will happen to the tropical summer monsoon belt as a whole extendshy

ing from West Africa to the Philippines over nearly half of the earths circumshy

ference It is quite difficult to find a convincing answer to this urgent

question affecting more than a quarter of the worlds population Paleoshy

clImatic data lre useless because of the very recent uplift of the Himalayas

mentioned above Obviously this uplift is still in progress but at a rate of

not more than a few (probably near one) centimeters per year which is neglishy

gible in its climatic effects during tile next century Because the temperashy

ture of the northern Indian Ocean is not likely to rise more than OS-loC (see

below) the meridional poleward temperature gradient above the Northern Hemishy

sphere will weaken and is not expected to influence greatly the Dummel- mOI1iuonal

circulation In fact the monsoonal circulation is driven by an oppositt jegtmshy

pt-tllre gradient (about 11 e per 30deg lat) at the upper troposphere UOO-500 mb)

between heated southern Tibet and the equatorial ocean (Flohn 1968 cf also

Reiter and Reiter 1981) In contrast to the slackening planetary circulation

of the Northern Hemisphere the monsoon circulation probably will either

retain or slightly increase its present intensity which is stronger than the

Northern Hemisphere Hadley cell At least it can be expected that the reversal

of the meridional temperature gradient which triggers the onset of monsoonal

flow pattern may occur sooner and remain later than now which should prolong

the duration of the rainy season

An important feature of the expected climatic pattern at a unipolar

glaciated globe is the possible role of equatorial upwelling Here we

start from the present situation during northern summersouthern winter when bull t~present asymmetry of the circulation reaches its peak The southern

trades encroach regularly on the (geographical) equator and push the ITeZ

towards lO-12degN (ie at about the same latitude as expected for its annual

average position with the unipolar glaciated earth) Since the trades cross

the equator where the Coriolis parameter f = 2~ sin cent (Q = angular volocity of

earths rotation) changes its sign the streamlines (practicall everywhere)

have a clockwise curvature which is cyclonic in the Southern Hemisphere but

anticyclonic in the Northern Hemispher2 Since the wind-driven Ekman drift of

the upper mixing layer of the ocean (to a depth of 50-100 m) is directed

perpendicular to the wind stress vector 1 the vertical component w of the -+

water at the bottom of this shallow layer depends on the vorticity curl z

together wHll f and the density of water p

S1

-1 w = (pf) curl T

z

This equation controls in a quite peculiar way the climatic conditions -+

in the immediate vicinity of the equator Since curl 1 is about constant at z

both sides of the equator and is negative the change of the sign of f leads

to a sudden shift of w at the equator At southern latitudes f lt 0 and w

becomes positive producing upwelling of cool water below the thermocline

while north of the equator f gt 0 and w becomes negative producing downwelling

In the present Atlantic (Henning and Flohn 1980) this leads to a marked

seasonally variable gradient in the latitude belt 0-4deg5 from June to October

SST becomes colder than the air temperature T due to upwelling and the flux a

Jf sensible heat depending on SST - Ta changes its sign to downward In regions

just south of the equator the difference between specific humidity of the air

at the seaair interface (q ) and of the air at the standard height of 10 m s above sea surface (q) becomes quite small leading to a remarkable drop of

evaporation depending on qs - q (Figure 12) JURt north of the equator both

fluxes of sensible and latent heat reach their highest values due to downwellshy

ing (and high radiation) Indeed the average daily evaporation increases

OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l

s tit 0 4~ I middot-Illlmiddot~ I - - Ui ~ bull laquo oL ---~Sn_ --- ~

~ - I

bull

-4 t$

-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I

J F M A M J J A S 0 N 0 J

Fil-ure 1 Annual trerC1 of evaroration (tlIlrJonth) 1at 2(l o[I-10 0 S

a1ung the snippinf route [uropemiddotmiddotSouth Africa eastern 1 t1antic datu from 1953-1965 (Lenning and Flohn 10)

~j2

d-ring July from 08 mrn at lOS [0 45 mrn at 5degN Small values below 1 mrn per

day were evaluated from the eastern equatorial Pacific (lat 0-3degS) south of

the Galapagos (~f Henning and Flohn 1980) In the case of a unipolar glashy

ciated earth similar conditions should be expected during a greater part of

the year This should lead to a substantial decrease of oceanic evaporation

concentrated at lat 0-5degS

At the central part of the Pacific Ocean (long l400W and north of

Tahiti) the upwelling zone is also concentrated immediately south of the

equator which is a consequence oE the large role of very small values of f in

the denominator Here the lowest SST (Figure 13) occurs even later between

August and January (cf isotherm +25degC) concentrated at lat lOS lJhile the bullhighest SST values between 2rand 28dege are observed in a broad seasonally

~1fting belt centered between lat 5degN (Nay) and BON (September)

ORAl) l1611

AVERAGE SEA SURFACE TEMPERATURES (OC) ALONG LONGITUDE 140deg W

N

12 ~ J ~-

_____ 26 __ -

----------- --I

---_-

27

)

I 8 r2

~- ---shy

8

bull4

---

o ~ -I ~- -- ---shy

-4 S

Feb Mar April May June July Aug Sept Oct Nov Dec JanJan

Fllure 13 SST along long 1400W (central Pacific) ITIonthly 11veragl-s from maps by Robinsun (1976) cf also Figure 4 Low temperatures centered at and just south of the equator lowest frequency of upwel1in~ AprilHlY highest between August and January Belt of highest temperat1Jres (cf Figure 3 meteorological equator) lat 4-8degN annua1 average 6 3degN

I 53

It should be noted here in passing that with the present solar constant

tropical SST data can hardly increase above 29degor 295degC If relative humidity

(~78) and the Bowen ratio (~03) are considered to be nearly constant the

available net radiation limits the possible amount of evaporation which

increases exponentially with temperature

From such considerations--based mainly on empirical data derived from

actual circulation parameters the author estimates as an educated guess and

subject to further modifications expected changes of precipitation (liP) and

the consequent temperature changes (~T ) for the scenario of an ice-free

s

~ Arctic These guesses (Figure 14) are made internally consistent as far as

possible without further investigations area-weighted averages of ilP = +5

of ~T +42degC The low value of ~P compared with the Manabe and Wetherald s

model is mainly due to the assumption of (more or less permanent) equatorial

upwelling This is indeed a crucial factor in our projection which ought to

be checked against a more complete survey of evidence from deep-sea sediments

which are quite difficult to interpret (eg Heath et al 1977) Berger

(1977 cf his Figures 22 and 24) notes an increase of accumulation rates in

the Miocene and Pliocene in spite of the opposing effects of increased fershy

tility (ie by upwelling) together with increased abyssal dissolution of

carbonates It is impossible here to enter into the discussion of the differshy

ences of carbonate sedimentation in the Atlantic and the Pacific

bull 90 ON

j 60j ff 30L

o I- x

30 ~ II

I II 60

901 III j I j Os

018852

r-shy~

r~1 r ~ ~

~l~ ~-

0 5 10 15 -20 0 20 40 60 80 100 Change In Change in

Temperature (OC) PrecipitatIon ()

Ftgurt 14 Projected changes of annual surf3ce temperalure (left in C) Clnd annui~l prlcipitation (right of present) in thv case of an ice-free rcf il Hcmgpounds of IIncert ainty shaded

c J-f

Figure 14 shows a strong increase of both T and P in Arctic and subarctic s

latitudes where the extension of high temperatures is somewhat larger than

that of precipitation It also shows an increase of rainfall in the northern

tropics centered near lat 15degN (ie a displacement of the tropical rainbelt)

while equatorial upwelling together with the (comparatively weak) shift of the

rTCZ should lead to a decrease of rainfall centered at lat 100S It should

be pointed out however that both excursions are rather conservative as are

the error bands Due to increased cloudiness and the SST maximum mentioned

above ~T should drop to a minimum at the belt of maximum rainfall around s

lat lOoN The belt of decreasing rainfall around lat 38degN (accompanied by

increased evaporation and temperature) should be of highest economic importance

h~ paleoclimatic evidence and model results converge convincingly Its

relative minor excursion is mainly due to the fact that the actual subtropical

winter rainbelt is indeed split into a number of isolated cells widely separated

by the near-permanent high-tropospheric troughs of the subtropical jet in

eastern North America and eastern Asia (Figure 9) TIlat indicates that in the

area of dominating winter rains the excursion must be multiplied with a factor

of about 2

The small temperature changes at the Antarctic continent are chosen

because of the presently very low water vapor content of the air even taking

into account a substantial advective rise and because of the weak warming due

to CO when decoupled from H 0 The Manabe and St ouffer (1980) model however2 2 bullsuggests a stronger warming at this area

These projected changes of annual temperatures and rainfall could probably

~3upplemented by some hints as to possible seasonal changes Figure 1

suggests that in the case of an ice-free Arctic the winter circulation could

be partly comparable particularly in lower latitudes to the present circulashy

tion pattern during fall (October) a similar reasoning has also been used by

Sergin (1980) With an ice-free Arctic the situation is different because of

the expected strong fluxes of latent and sensible heat from an open Arctic

Sea Spring is less comparable than fall the present frequency of strong

Arctic anticyclones during spring--with average surface pressures above 1022

mb--is not fully understood but seems to be linked with the late seasonal peak

of the snow-ice distribution during Harch For the projected summer situation

no actual comparison is available

I CHAPTER 6

SUGGESTIONS FOR FURTHER RESEARCH

As outlined in Chapter 4 two major climatic events must be considered

as possible consequences of a CO -induced global warming In recent years2

the possibility of a partial collapse of the West Antarctic ice sheet has been

widely publicized with major emphasis being given to the resulting sea-level

rise The climatic consequences of this ice collapse promise to be much less

106 3significant To melt an ice mass of 2 x km (equivalent to a sea-level

rise of about 5 m) split into many icebergs dispersed widely over the large 6 2subantarctic oceans (estimated area 30 x 10 km) requires a total energy

1021-mput of 160 x gcal If a layer 100 m thick participates in this melting 2its heat loss per unit of surface area would be 53 gcalcm If the melting

takes place over 10 years this layer should cool about 5degC assuming all

other factors remain constant If the melting were to occur over 100 years

the average cooling of the layer would be only 05degC This limited cooling of

the subantarctic waters would locally influence the climate of the isolated

islands of the Far South including southernmost South America and the

southern tip of New Zealand It would also intensify for a limited period

the (already very strong) atmospheric circulation of the Southern Hemisphere

together with the circum-Antarctic ocean current The strong interannual

variability of the climate and sea-ice record in those areas (eg Laurie

Island now replaced by Signy Island at lat 6l 0 S) suggests that these

xpected changes probably will not be much larger than during extreme years of

he last two centuries (cL Lamb 1967 Limbert 1974)

Turning from the problem of a partial collapse of the Antarctic ice it

seems to be of vital interest and at a high level of priority to investigate

the geophysical background of a possible decay of the Arctic sea ice Instead

of a survey of all available sea-ice models since Maykut and Untersteiner

(1971) only two models need be discussed These yield the development of a

seasonal melting of the Arctic sea ice under the influence of increased CO2

(Manabe and Stouffer 1979 1980) or (the equivalent) caused by increasing

temperatures of atmosphere and ocean (Parkinson and Kellogg 1979)

Manabe and Stouffers climate model includes a motionless mixed-layer

ocean with a constant depth of 68 m which has been carefully selected for the

purpose of accounting for the seasonal storage of heat The simulation of the

)6

~easonally varying sea-ice area in the standard case deviates somewhat from

the observed data in the Northern Hemisphere the area tends to be too large

in the Southern Hemisphere too small Furthermore the sea-ice thickness

during late summer and fall is too small compared with observations and more

complete models (Maykut Dnd Untersteiner 1971 Parkinson and Washington

1979) The occurrence of seasonal melting (June) and refreezing (Novembershy

December) 1s consistent with the intentionally selected depth of the mixedshy

layer ocean Several authors (Donn and Shaw 1966 Vowinckel and Orvig 1970

Flohn 1980) have attempted to evaluate the heat budget of an ice-free Arctic

Ocean With some reasonable assumptions one obtains for the whole year a

positive heat budget In this case an energy surplus is available for storage bull~n the sea during an expected transitional stage with a seasonal ice cover as

~uggested by the above-mentioned models A simple estimate (Flohn 1980)

assumes an annual net surface radiation of 45 Wm~ of which 40 percent is used

during the summer for evaporation when the sensible heat flux is either

downward or small tile remaining 27 Wm2 (V 20 kcalcm2yr) are available for

heat storage in the sea Assuming all other factors to remain constant this

would yield for a 50 m thick low-salinity surface layer a seasonal heat

storage of 4 calg equivalent to a warming of 4n C in a single summer Such

an efficient storage of heat is likely because during summer the sea remains

cool compared with the adjacent continents A more or less permanent thermal

circulation should develop with subsidence and low cloudiness over the sea

allowing the dark sea to absorb 85-90 percent of the incoming radiation and

reaching after each melting season a new equilibrium stage at successively bull ~ncreasing temperatures

Once equilibrium is reached the expected heat surplus of an ice-free

Arctic Sea will be available for export into adjacent continents which are

certainly during winter and spring snow-covered and much cooler than the

sea Budyko (1977) has estimated an annual SST near 8degC this estimate seems

to be consistent with paleoclimatic data from northeastern Siberia and Banks

[sland which (see sections 33-35) suggest a sununertime air temperature near

12 C Monmndel studies arv needid allowing for interannlll] heat storay III

ttl( ocean and for an increase of the hEH flux from the ocm 1n amollnts well 2

abov~ the 25 Wm selected by Parkinson and Kellogg (1979) Here representative

values from the area of the Norwegian Current could be taken However it

seems to be more appropriate to estimare the heat fluxes from a deep (not

57

stratified) ocean with an annual average SST of sOe assuming seasonally v~rying

advection of air with winter temperatures (eg down to -20 0 below an 850 mb

inversion) A comparison of the above-mentioned heat budget estimates with

Parkinson and Kelloggs model indicates that the ocean heat flux will most

probably provide the clue to our problem The Manabe and Stouffer model might

be used for experiments where an increase of the depth of the mixed layer

(probably restricted to the ice-covered area) is incorporated

An additional problem must be considered the possible role of a reduced

freshwater inflow into the Arctic Sea for its internal stability The present

oceanographic situation is characterized by a thin (30-60 m) low-saline and

thus less dense surface layer The Atlantic waters transported by the Norwegian

-Current are a few degrees warmer (+2 to 3dege instead of -18degC) than this upper

layer but more saline (34-35 percent instead of about 30 percent) and thus

more dense submerging below the upper layer which owes its low salinity

partly to the dilution by river water from the continents partly to the

continuous meltingfreezing processes extricating heavy brines from the sea-

ice At present a balance exists between the seasonal inflow of fresh meltwater

from the Siberian and Canadian tivers and outflow of surface water (and sea

ice) via the strong baroc1inic East Greenland Current Because of the urgent

need for more irrigation water available in its arid central Asian territory

serious plans are under development in the USSR to divert several large rivers

with an enormous canal system--through the low-level Turgai gap This was

once a large meltwater channel from the Siberian ice 18 ka ago (Grosswa1d

1980) Plans have been developed (Hollis 1978) to provide for a diversion of

~uP to 300middot km 3 per year of fresh water from both the Ob and Yenissei catchments

An annual diversion of 300 km 3 from the present runoff into the Kara Sea would

mean a reduction by as much as 23 percent This would gradually increase the

salinity of the upper layer of the sea thus reducing the density stratificashy

tion and increasing vertical mixing Once the stage of a well-mixed ocean is

reached only a seasonal ice cover appears to be possible as is now the case

in the vast southern oceans Eighty-five percent of the present subantarctic

sea ice is seasonal produced by the combined effects of advective cooling

from the Antarctic continent and the negative radiation balance

Since no model calculations of the salinity changes by these processes

are available a quite simple extrapolation may give a hint to the time scale

involved Assuming the net outflow of lOW-saline water and ice to remain

constant while the inflow reduces by 300 km 3 per year the shortfall in the

lb

~n~low must be replaced by vertical mixing and uplift of high-saline Atlantic

water from below Since the total volume of the low-saline layer can be 6 3

estimated to be 005 (thickness) x 10 x 10 (area) km 3 = 5 x 105 km an

3annual replacement of 300 km would need about 1700 years before a total

exchange could be completed More complete calculations would certainly

improve confidence in the result and should take into account the weak relation

between temperature and density at temperatures near OdegC However this crude

estimate indicates that this process is not negligible but is relatively slow

in comparison with the time scale of the expected changes in the composition

of the atmosphere and in its infrared radiation budget

In addition to these model studies the highly asymmetric climate just

before the onset of large-scale Northern Hemisphere glaciation needs a much

m~ complete investigation This investigation should be based on all avail shy

able evidence from the continents as well as from the oceans Although the amount

of such evidence is now rapidly increasing a quantitative assessment with

estimates of climatic parameters based on carefully checked transfer functions

is frequently lacking especially for land biota where the need for this data

is particularly high It seems to be advisable to have paleobotanists

paleozoologists and paleoceanographers working together with climatologists

(in an effort similar to the successful CLIMAP program) useing all available

data and techniques to investigate the background of the climate of the late

Mioceneearly Pliocene between 6 and 35 Ma ago The specific goal should be

the preparation of a series of climate maps with best estimates for specific

parameters such as summer and winter temperatures and annual amount and bull se-onal patterns of precipitation Such maps should be interpreted and

improved with the help of geologists and physical geographers familiar with

the evolution of mountain building and related topics It should be possible

to prepare such maps after a working period of 3-4 years including well-

planned data collecting expeditions at selected points Some existing research

programs--such as the coring of closed lakes--could be of great value in this

work One of the key problems would be an assessment of the time variations

of the productivity of equatorial oceans

The purpose of such paleoclimatic maps is twofold They can serve as

model scenarios for much needed studies on the impact of climatic change on

agriculture water supply forestry fishery and many other economic issues

of interest especially the evolution of the ocean currents under the influence

59

of a much weaker atmospheric circulation in the northern hemisphere Secondly

they can serve as background data against which climate models must be tested

if they are to be considered sufficiently realistic Without this background

model results remain rather vague are subject to many uncertainties and lack

the degree of trustworthiness needed for long-range decision-making

I CHAPTER 7

SUMMARY AND CONCLUSIONS

The purpose of this review has been to discuss the geophysical and

historical background of two major climatic changes that occurred in the

geologic past and may possibly recur in the future under the expected influence

of a CO -induced global warming These two events are (A) the disintegration2of the West Antarctic ice sheet and (B) the disappearance of the slallow

drift ice of the Arctic Ocean

Event B would lead to a unipolar glaciation with a high degree of climatic

~ asymmetry The present climatic asymmetry between the two hemispheres was disshy

cussed in Chapter 2 together with some of the particular patterns of atmospheric

and ocean circulation in the equatorial regions Oceanic upwelling of cool

water near the equator in both the Atlantic and Pacific Oceans is one of

the important geophysical consequences resulting in the formation of a

strong equatorial countercurrent only in the Northern Hemisphere Averaged

over the whole year and all longitudes the meteorological equator shiftH

to lat 6degN while the stronger atmospheric circulation of the Southern Hemishy

sphere encroaches on the (geographical) equator during most of the year

In recent years paleoclimatic evidence has revealed a quite different

t history of the glaciation in the two polar regions (Chapter 3) The Antarctic

continent remaining nearly at its present position for more than the past 50 Ma

~ first became partly glaciated 38 Ma ago Simultaneously there was a marked

cooling at the ocean bottom allover the globe and at the higher latitudes of

both hemispheres During a second marked cooling about 15 Ma ago associated

with a period of high volcanic activity the glaciation of Antarctica expanded

over nearly the whole continent Only the archipelago of Western Antarctica

remained ice-free until the peak of the Antarctic glaciation about 6 Ha ago

when its total ice volume was probably 50 percent greater than now This

accumulation of ice resulted in a sinking of the worlds sea level repeatedly

desiccating the Mediterranean

In contrast to that long evolution the Arctic sea ice was formed only

about 24 Ma ago most probably as a consequence of the first large-scale

glaciations of the northern continents The glaciations were triggered by the

closure of the land bridge of Panama about 32-35 Ma ago which caused an

62

ihtensification of the Gulf Stream with its moisture transport One of the

main prerequisites for permanent (rather than seasonal) sea ice was the formation

of a shallow low-saline upper ocean layer produced by the seasonal melting of

glaciers and the internal processes of freezing and melting The stability of

the present sea ice has probably been restricted to the last 07 Ma

Thiti abbreviated history reveals that during a very long time of more

than 10 Ml the Antarctic continental glaciation coexisted simultaneously with

an ice-free Arctic Ocean and that the climatic asymmetry between the poles

mUHt hnve been much greater than at present There was no tundra nor permilshy

frost at bih latitudes in the northern continents instead a rather rirh

forest grew there indicating summer temperatures near lZoC Since the intensity bull

jI the atmospheric circulation and the position of the climatic belts both

Hipend on the temperature difference between equator and pole the climatic

pattern must have been substantially different from now Indeed tbere is

evidence for a northward extension of the northern arid belt as well as for a

complete shift of the equatorial rainbelt to the northern tropics the latter

would be correlated with increased aridity in the southern tropics up to near

the equator

The ltivai 1able paleoclimatic evidence suggests that both major cJ tmal ie

events were associated with a general (global) temperature rise of between 4deg

and SoC (Chapter 4) Comparing selected model results of the CO2-temperature

relation (see the appendix) yields a semilogarithmic diagram that describes an

approximate relation of these two quantities dependent only on one combined

model-derived parameter which also takes into account the greenhouse effect bull ~ other infrared-absorbing trace gases and its possible increase with time

If a 4degto SoC increase in the globally averaged temperature is assumed as a

realistic threshold above which the risk of both major climatic events increases

significantly this could middotresult from a CO concentration slightly above 6002

bullbullppm (eg bullbull 620 ppm 2 lOX) This revision of former higher estimates (Flohn

1980 7S0 ppm + 16) is mainly due to the probability of an increasing role

of greenhouse gases other than CO The uncertainties of the future developshy2

ment or ellergy deniand Jne the uncertRinties within the carbon cycle regarding

tlH plrtllloI11n~ of carbon omong atmosphere ocean biosphere and setllments bull rllllilin ns grtat lS or greater than those still within the CO-climare nJationshy

ship bullbulli

j bull I

6

A general global temperature rise of 4-5degC seems to be an appropriate

base--even if based on different reasoning--for estimating the risk of both

m1jor events A and B This tempera ture rise will be 2-3 times as great in

hi)h IIOr tlern lat itudes the expected increase near the Antarctic wi 11 he

much llmaller

Both events are part of our climatic history the last case of a collapse

of the West Antarctic ice sheet (Event A) occurred in the middle of the last

interglacial warm epoch about 120 ka ago The Arctic Ocean was last ice-free

(Event B) about 24 Ma ago we do not know if it became ice free again even

bull

~ for shorter time periods but it certainly did not after 07 Ma ago This

seems to indicate that in the future Event A should be expected earlier than

~ Event B However the author selects several arguments which indicate that a

reversed sequence--B earlier perhaps much earlier than A--is more likely

His argumentation is mainly based on the different time scales needed for the

preparation and for the geophysical processes involved The high spatial

variability of the extent of the Arctic sea ice during the last 1000 years

seems to indicate that the thin sea ice is much more sensitive to climatic

change than big continental ice sheets or ice shelves

A first-order scenario of climatic changes to be expected in the case of

an ice-free Arctic Ocean (Chapter 5) is based on paleoclimatic evidence and on

some coherent results from climatic modeling Expected shifts of climatic

belts are derived from a simple relation between the meridional temperature

gradient in the troposphere and the position of the subtropical anticyclonic

belt which is related to V Bjerknes fundamental circulation theorem Based

~ on this background the expected displacements of the major climatic zones are

estimated These serve as a base for a conservative estimate of changes in

annual rainfall and temperature both as a function of latitude A simple

extrapolation of paleoclimatic data cannot be applied since some climatic

boundary conditions--mountain uplift closing of the Panama land bridge--have

changed significantly since the comparison period of the late Miocene and the

early to mid-Pliocene (6-35 Ma ago)

Because such an unexpected and strange climatic pattern of a unipolar

glaciated earth could occur after a short transition period (probably in the

order of a few decades only) as a result of a limited increase in CO concenshy2

tration its investigation should be given a much higher priority Some

suggestions are given (Chapter 6) to modify existing models so as to indicate

64

the possible occurrence of seasonal (instead of permanent) sea ice with storage

of incoming solar radiation in a dark sea (with only small amounts of cloudiness

during summer) leading inevitably to higher sea surface temperatures and ulti shy

mately reducing the regime of seasonal sea ice to a short transition period

The diminution of the freshwater inflow from Siberian rivers will further

reduce the formation of permanent ice but at a much slower rate Finally

suggestions for intensified paleoclimatic research are given quantitative and

worldwide data can be derived which after a critical assessment of the role

of changing boundary conditions may provide educated guesses as well as

verification data for climate modeling

In view of the fundamental changes of climatic patterns in the case of a

~ipolar warm (or unipolar glaciated) earth climate models are or at least

r~omise to be powerful tools However even their most comprehensive examples

necessarily contain simplifications In this situation we should remember

that nature alone can solve the complete set of equations without neglecting

important feedbacks without crude parameterization of sub-grid-scale effects

and on-line (but on her own time scale) Parallel to modeling the historical

evolution of climatic processes is another equally useful key to understand

climatic change It is rather promising that some of the results of most

realistic climate models after critical assessment coincide rather well with

projections derived from paleoclimatic history

~ bull

1 APPENDIX

A MODEL-DEPENDENT CO -TEMPERATURE DIAGRAM2

The multitude of uncertainties in the CO issue can be split into three2

categories

1 Uncertainty about the future trend of consumption of fossil fuel

2 Uncertainties about the role of the biosphere and oceans in the

carbon cycle

3 Uncertainties about the relationship between atmospheric CO2 and

climate

In this report only category 3 is considered Many investi~ations--~ especially with simplified models (zero one or two dimensions)--concentrate

on the globally averaged increase of surface temperature (T ) due to increased s

CO2

Other (more complicated) models try to evaluate more specifically the

changes of other climatic parameters such as rainfall and wind patterns In

the text of this report it has been shown that the latitudinal patterns of the

atmoRpheric circulation of winds and rainfall depend on the vertically averaged

meridional temperature difference r which is--within certain limits--directly

related to T through the ice-albedo-temperature feedback mechanism Global s average surface temperature T bull is indeed a basic parameter and its relation

s to the atmospheric CO level is of paramount importance2

Washington and Ramanathan (1980) have demonstrated how the greenhouse

effect of CO2 is inherently coupled with that of H 0 and that the coupled effect2

is more powerful than that of CO alone There are other infrared-absorbing2 trace gases that add to the total greenhouse effect without being immediately

coupled with CO2 Among them we should mention N 0 CH4

tropospheric 03 and 2

the chlorofluoromethanes (Freons) These gases absorb in the atmospheric

window regions notably between 75 and 12 urn (Wang et al 1976 Ramanathan

1980 MacDonald 1981) It has been proposed (Flohn 1978b) to simply add 50

percent or 100 percent to the CO2-induced greenhouse effect in order to take

account of these gases But such a constant factor would be justified only in

the case of a strong coupling between their effects

In a workshop held at Munster (W Bach et al 1980 see p xXetc) a

simple logarithmic relation between T and the CO content was suggesteds 2

Using this relation and papers by Gates (1980) Ramanathan (1980) Washington

6h

and Ramanthan d980 and Hoffert et a1 (1980) a simple ltiiagram given here

(see below Figure A-l) allows a first-order estimate of T as a function of s

the CO -level and some model-derived parameters2

Starting from the extraterrestrial radiation balance equation

Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m

with SC = solar constant Q = net extraterrestrial solar radiation a = p

planetary albedo and E = terrmiddotestrial (infrared) radiation to s~~ace we omit

an evaluation of the different contributions (surface albedo clouds dust) to

a (which is given elsewhere) and assume a near equilibrium of Q If anyp

deviation from an undisturbed reference level is denoted by ~ then for equishy

~_ibriurn ~E~ can be written as follows

~E = B ~T - n C InA = 0 (2)s

~C02 In this equation A denotes the normalized CO level (A = 1 + CO B and C

2 2

~E(all IR-absorbing gases)are model-dependent sensitivity parameters while n = ~E(CO ) 2

corrects the CO2-greenhouse effect due to the role of other infrared-absorbing

trace gases (Ramanathan 1980)

Several authors have estimated the different sensitivity parameters The

following list (Table A-I) is certainly not complete (see also Gates 1980)

It is restricted to a few papers by Manabe and Wetherald (1975) Ramanathan et bull ~1 (1979) Madden and Ramanathan (1980) and Hoffert et al (1980) B is

-1frequently given as A = B (thermal sensitivity) C depends on B and on the

tenlperature increase given by the climate model for a change in CO (see2

formulas given by Hoffert et al 1980 p 6670)

Because the Ad Hoc Study Group on Carbon Dioxide and Climate (1979)

favors a higher temperature response to CO doubling (A = 2) the author2

prefers also higher values for C His estimates are

tiE -2 -1B l 18(jO4) Wm KliT s

I

67

Table AI Model-Dependent Sensitivity Parameters

Authors B C Da

Ramanathan Lian and Cess (1979) 16 412 257 33-44

Madden and Ramanathan (1980) 1-4 59 + I 15-7

bManabe and Wethera1d (1975) 195 824 423 55-72

Hoffert Callegari and Hsieh(1980) 22 793 361 47-61

aCaIculated with CB and n = 13-17 (see equation 3)

bDerived from Wetherald and Manabe (1975)

08

and C

~E V 68(+12) wnC0 - 2

2 rn

Ramanathan (1980) gives several values for n dependent upon the selection

of a reference value of CO2 Here we prefer to select a reference level of

300 ppm then n is estimated to be Vl3 now and to increase during the next

50-60 years to Vl7-l8 (Ramanathan 1980 MacDonald 1981) Such a timeshy

dependent increase--mainly produced by the long atmospheric residence time of

the Freons and by the expected increase of N 0 due to growing use of fertilizers-shy2

seems to be more realistic than the use of a constant factor n 15 which is

equivalent to an earlier proposal (F1ohn 1978b) It should be mentioned

~at according to recently published measurements from undisturbed places

(Rasmussen et al 1981) the atmospheric concentration of Freons is increasing

by 8 percent annually and N 0 is rising by 05 percent annually both in the2

ppb range while CO is increasing annually by about 04 percent2 [f 6E is assumed to be zero equation 2 is transformed into 3

nC ~T = - InA D InA (3)

s B

with D as a combined parameter this can easily be represented in a semilogarithshy

mic diagram (Figure A-I)

In this diagram the assumed critical levels of ~T 4-5degC are givens

nCparallel to the abscissa crossed by the radii labeled D = S With the

preliminary values mentioned above ~ becomes V38 using all available estimates bull ~ B C and n D may vary between about 3 and 9 Starting from a present

figure n (greenhouse gases parameter) 130 (Ramanathan 1980) we obtain

a most likely figure for D of about 5 If n as expected should increase to

near 17 D will rise to 62 or even 65 In Figure A-I we have assumed that D

will reach 62 by the time the CO level reaches 500 ppm the dashed line shows2 the assumption It starts at 300 ppm with D ~ 5 depicts increasing D up to

CO2 levels of 500 ppm and assumes D to remain at 62 thereafter If these

assumptions are correct then the assumed critical 6T thresholds will be s

reached at a CO 2 concentration between about 570 and 670 ppm Assuming a

further rise of n then the upper limit of the critical level might only be

650 ppm This indicates that the former estimate of a CO -risk level of 750 2

119

ppm ~ 16 (Flohn 1979 1980) may be too high Note that the above limits

include the 600 ppm level (A = 2) used in many model calculations

Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm

Figure A-1 Atmospheric CO2 and Surface Temperature Change 6Ts o = nCB (model-dependent)

It must be admitted however that most of the projections of the growth

rate of other greenhouse gases are even more uncertain than the projections

of CO growth rates aminly due to our incomplete knowledge of the multiple2 chemical processes involving 03 and OH in the atmosphere which renders any

future eRtimate of n rather doubtful At any rate Figure A-I together with

more reliable est imates of the three p-3rameters involved wi 11 allow fi rat-order

guesses of the climatic role of the complete greenhouse effect The role of

the terms contributing to the planetary albedo a (equation 1) has been disshy p cussed elsewhere (Flohn 1981 b)

Perry et al (1981) have ind icated that it may become necessary to

limit atmospheric CO2 to 15-25 times the present concentration (Ie to a

level between about 500 and 800 ppm) This investigation indicates a critical

70

ttll~eshnld at a level slightly above 600 ppm that is at 620 (lO) ppm

Above thil level the risks may be intolerably high The role of all greenshy

house gases obviously is of great importance for every consideration of the

CO~-cl imate issue

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Wilson A T 1964 Origin of Ice Ages An Ice Shelf Theory for Pleistocenp Claciation Nature 201147-149

Wolfe 1 A 1978 A Paleobotanical Interpretation of Tertiary Clillk1tes 1n the Northern Hemisphere American Scientist 66094-703

Wolfe J A 1980 Tertiary Climates and Floristic Relationships at High Latitudes in the Northern Hemisphere Palaeogeography Palaeoclimatology Palaeoecology 30313-323

Wolfe J A and E B Leopold 1967 Neogene and Early Quaternary Vegetation of Northwestern North America and Northeast Asia pp 193-206 in D M Hopkins ed The Bering Land Bridge Stanford Ca1jfornia Stanford University Press

Wood ru ff F S M Savin and R G Douglas 1981 Miocene Stable Isotope Htlord A Detail ed Deep Pacific Ocean Study and Its Paleoclillllti( fmp1lcations Science 212 665-668

Worsley T R and Y Herman 1980 Episodic Ice-Free Arctic Ocean in PHocene and Pleistocene Time Calcareous Nannofossil ~vidence Scienc~ 210 323-325

Wyrtki Kbull E Firing D Halpern R Know G J McNally W C Patzert E D St rOllp B A Taft and R Williams 19R1 The Hawaii to Tahiti Shuttle Experiment Science 211(4477)22-28 bull

61pdf

62

63

64

-----bull

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MAJOR CLIMATIC EVENTS ASSOCIATED WITH A PROLONGED CO -INDUCED WARMING2

ABSTRACT

The climates of earlier geologic times may provide useful analogues

for future cUmates tnat could follow global warming induced by CO2

rn

pnrticulnr two climatic events are possible if CO conrentrations reach2

levels ahove 600 ppm and if other greenhouse gases increase simultaneously

leading to an increase of 4-SoC in global average temperature One

- ~vent the disintegration of the West Antarctic ice sheet last occurred

about 120 thousand years ago The other the disappearance of the

shallow drift ice in the Arctic Ocean last occurred about 24 million

years ago Although this suggests that the West Antarctic ice is more

fr~gile than the Arctic sea ice the events may occur in the opposite

order Disappearance of the Arctic sea ice appears to require a shorter

preparation time during and after the temperature rise and hence may he

antIcipated first

The dislppearl1nce of the Arctic sea ice would constitute a case of

unl po lar glH La t i0n Paleoclimq tic ev idence suggests tha t the lltJ rtl has

fxperienced long periods of unipoIqr glaciation and that the effects of

Stich radicbull l asymmetry on global climate would be far-reaching Chief

among them would be shifts in the major climate zones especially a

northward displacement of the intertropical convergence zone and the

suhtropical anticyclones by 2deg or more This shift would produce seasonal

temperature and precipit~tion p8tterns-quite different from current

ones with si~nificant drying and warming in the 35-45degN latitude hAnd

Such changes could have serious implications for human activities

bull

TABLE OF CONTENTS

Page










Events


Events n




App(mdlx bullbull

References 71

ii i

bull LIST OF TABLES







v

LIST OF FIGURES













2


vii

~-

~





III II III

bull

bullbullbullbull

ix bull

ACKNOWLEDGMENTS












CHAPTER 1

I NTRODUCT ION
































--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



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categories



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300 400 500 600 700 800 1000 1200 ppm












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CO~-cl imate issue

REFERENCES








2








72









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61pdf

62

63

64

bull

TABLE OF CONTENTS

Page










Events


Events n




App(mdlx bullbull

References 71

ii i

bull LIST OF TABLES







v

LIST OF FIGURES













2


vii

~-

~





III II III

bull

bullbullbullbull

ix bull

ACKNOWLEDGMENTS












CHAPTER 1

I NTRODUCT ION
































--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










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20 25 30 36 40 45

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11













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with other oceans

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Eocene

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Early Miocene

- 22 x 106 yn ago

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19

































20









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this short review







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Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

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23




















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24




































~

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25


































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I

bullbull

mrs

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27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

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30

40

o 18 24

K 29 33

Age (Ma)


bull





















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data (Chapter 5)

CHAPTER 4





possible key issues



























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completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

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+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

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300

2 2 3

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3 33 300 5 5

600

900S

















47

02 ORAU 81861

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6





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bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

bull LIST OF TABLES







v

LIST OF FIGURES













2


vii

~-

~





III II III

bull

bullbullbullbull

ix bull

ACKNOWLEDGMENTS












CHAPTER 1

I NTRODUCT ION
































--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

bull













49


























chapter










50




































S1

-1 w = (pf) curl T

z
















OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l


~ - I

bull

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-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I




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12 ~ J ~-

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bull4

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I 53










s













bull 90 ON

j 60j ff 30L

o I- x

30 ~ II

I II 60

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018852

r-shy~

r~1 r ~ ~

~l~ ~-




c J-f


















of about 2

















I CHAPTER 6

































)6



































57






































lb




































59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

LIST OF FIGURES













2


vii

~-

~





III II III

bull

bullbullbullbull

ix bull

ACKNOWLEDGMENTS












CHAPTER 1

I NTRODUCT ION
































--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

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49


























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50




































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8

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j 60j ff 30L

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59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















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1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

~-

~





III II III

bull

bullbullbullbull

ix bull

ACKNOWLEDGMENTS












CHAPTER 1

I NTRODUCT ION
































--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

bull













49


























chapter










50




































S1

-1 w = (pf) curl T

z
















OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l


~ - I

bull

-4 t$

-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I




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N

12 ~ J ~-

_____ 26 __ -

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8

bull4

---

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I 53










s













bull 90 ON

j 60j ff 30L

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of about 2

















I CHAPTER 6

































)6



































57






































lb




































59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

ACKNOWLEDGMENTS












CHAPTER 1

I NTRODUCT ION
































--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

bull













49


























chapter










50




































S1

-1 w = (pf) curl T

z
















OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l


~ - I

bull

-4 t$

-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I




~j2













ORAl) l1611


N

12 ~ J ~-

_____ 26 __ -

----------- --I

---_-

27

)

I 8 r2

~- ---shy

8

bull4

---

o ~ -I ~- -- ---shy

-4 S



I 53










s













bull 90 ON

j 60j ff 30L

o I- x

30 ~ II

I II 60

901 III j I j Os

018852

r-shy~

r~1 r ~ ~

~l~ ~-




c J-f


















of about 2

















I CHAPTER 6

































)6



































57






































lb




































59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

CHAPTER 1

I NTRODUCT ION
































--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

bull













49


























chapter










50




































S1

-1 w = (pf) curl T

z
















OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l


~ - I

bull

-4 t$

-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I




~j2













ORAl) l1611


N

12 ~ J ~-

_____ 26 __ -

----------- --I

---_-

27

)

I 8 r2

~- ---shy

8

bull4

---

o ~ -I ~- -- ---shy

-4 S



I 53










s













bull 90 ON

j 60j ff 30L

o I- x

30 ~ II

I II 60

901 III j I j Os

018852

r-shy~

r~1 r ~ ~

~l~ ~-




c J-f


















of about 2

















I CHAPTER 6

































)6



































57






































lb




































59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

--

































3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

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49


























chapter










50




































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bull 90 ON

j 60j ff 30L

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I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

3




































4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

bull













49


























chapter










50




































S1

-1 w = (pf) curl T

z
















OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l


~ - I

bull

-4 t$

-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I




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N

12 ~ J ~-

_____ 26 __ -

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8

bull4

---

o ~ -I ~- -- ---shy

-4 S



I 53










s













bull 90 ON

j 60j ff 30L

o I- x

30 ~ II

I II 60

901 III j I j Os

018852

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c J-f


















of about 2

















I CHAPTER 6

































)6



































57






































lb




































59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

4
















CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

bull













49


























chapter










50




































S1

-1 w = (pf) curl T

z
















OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l


~ - I

bull

-4 t$

-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I




~j2













ORAl) l1611


N

12 ~ J ~-

_____ 26 __ -

----------- --I

---_-

27

)

I 8 r2

~- ---shy

8

bull4

---

o ~ -I ~- -- ---shy

-4 S



I 53










s













bull 90 ON

j 60j ff 30L

o I- x

30 ~ II

I II 60

901 III j I j Os

018852

r-shy~

r~1 r ~ ~

~l~ ~-




c J-f


















of about 2

















I CHAPTER 6

































)6



































57






































lb




































59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

CHAPTER 2











Table 1


Equator ( F)

North Pn]t (N)

January

ne1rl v consta

-415

July

nt at

-259

Annual Average

-Rt)

-359

South Pole (5) -3R3 -527 -477









bullbull

III III

bull lIP






























ROSSDY number ROT

=

bull




South Pole 2800 -323 -582 -493 -15-81 52 38 1957-66

Vostok (78degS) 3488 -368 -670 -556 -21-88 38 33 1957-66



Subpolar Zone

Orcadas (61degS) 4 00 -101 -44 +12-40 93 79 1903-68

Ivigtut (61degN) 30 +90 -46 +18 +23-23 65 63 1931-56



-I

II

bull



Arc

Radiation






Heat


bullII





I I I I

9







j


























bullbullbullbull





10









15


the latitudinal

the latitude

of a mathematical

the sets of

thus only a










OAAU1756

Mx


r shy 0865

20 25 30 36 40 45

oneshy

from




_


- (I


11













OFIAU 81756

80deg

(aTaz60deg G)

Q J co J 40deg






bullbullbull

l2



Hemisphere





sections) merge










(rigure 3)

ORAU 81761

Annual 0---shy

5deg Fshy

R o ~ (Tw + V + -lt + R )



bull

bullbull III


13













with other oceans

OAAU 81112


N

12

8

o

-4 5



II

I

CHAPTER 3























sent ones


investigilterl







crisis



l6



































bullbullf


17





































bullbullbull


(I UP W

18











-

~~~- -

-bull lt



Eocene

~----~------~----~~----~-----


20degC


ORAU Bl 1 1015

Pleistocene


late Miocene


Early Miocene

- 22 x 106 yn ago

bullbullbull1(


19

































20









OR AU 81752

--~- --shySlIIlitl


bull bull

e bull III



21










this short review







ORAU 817153

Non-Glacial Present

30

25

C3 20

~ 15 i 10 i ~ 5

65 o


35

30

25

20

15

10

5

60 55 50 45 40 35 30 25 20 15 10 5 Ma

bull bull

bullbull
























23




















(OKeefe 1976)















bull bull bull bull

24




































~

I i

25


































54QN



I

bullbull

mrs

26 bull























27

OR AU 81754

Depth in Core (m)

10 12 14 16 18 20

bull

III 0 Q

0

e 0

0 IX) co

30

40

o 18 24

K 29 33

Age (Ma)


bull





















bullbullbull























2Y











are needed




























































It



data (Chapter 5)

CHAPTER 4





possible key issues



























t III





















bullbull i











J)








completely





























lh




































37



































CHAPTER 5

































40



tlf -kAT s


































bullbull

42
































~l




+4degC 14 -56 -84 -2se 390 373 421

17 -6S -102 -34 395 382 424

+5degC 14 -70 -105 -35 397 383 424

17 -85 -128 -43 405 397 432

rshy(


44






























I 45










latitudes



























bullbull

j() bull shy

OAAU 81864

9OoN

600 5

5 4 34

300

2 2 3

1 00 1

22

3 33 300 5 5

600

900S

















47

02 ORAU 81861

4 x CO2

--- - 2 x CO2 1 x CO2

I -gtshy I

I ~ u1 ~ - --shy ~

w I I

cI

o I 90 I -e I

sao 700 600 5()0 400 3()0 200 100 00 Latitude







bullbull

4)

ORAU 81863

bull













49


























chapter










50




































S1

-1 w = (pf) curl T

z
















OFlAU 8882

Ci~F20 i- ~

bull 16

12 1 Ill

8 4l


~ - I

bull

-4 t$

-8 I ~ ~

lt eo 06 ~~ ~ - 12 1 0

I 9

I




~j2













ORAl) l1611


N

12 ~ J ~-

_____ 26 __ -

----------- --I

---_-

27

)

I 8 r2

~- ---shy

8

bull4

---

o ~ -I ~- -- ---shy

-4 S



I 53










s













bull 90 ON

j 60j ff 30L

o I- x

30 ~ II

I II 60

901 III j I j Os

018852

r-shy~

r~1 r ~ ~

~l~ ~-




c J-f


















of about 2

















I CHAPTER 6

































)6



































57






































lb




































59






I CHAPTER 7

































62


















the equator















ship bullbulli

j bull I

6





much llmaller





bull




























64






















~ bull

1 APPENDIX



categories



carbon cycle


climate



CO2






















6h





Q (1 _ a ) SC -E (El240 ii + 1) (1)P 4 2

m







~E = B ~T - n C InA = 0 (2)s


2 2














I

67


Authors B C Da







08

and C

~E V 68(+12) wnC0 - 2

2 rn














s B















119



Ts --- ------ OAAU 81851

14

12

10

bull 8

6 4

2

o -1

-2 -3

200

bull

Critical 6 T s

0=9

8

7

6

300 400 500 600 700 800 1000 1200 ppm












70




CO~-cl imate issue

REFERENCES








2








72









2








bull

III

n
















bull

74







2










I

75

















_- 76 bull















77















t

7H




2
















79
















80















61pdf

62

63

64

MAJOR CLIMATIC EVENTS ASSOCIATED WITH A -INDUCED …

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Transcript of MAJOR CLIMATIC EVENTS ASSOCIATED WITH A -INDUCED …