Greenhouse gases in the Quaternary: constraining sources, sinks, feedbacks and surprises

Eric Wolff1 and the QUEST-DESIRE team1. British Antarctic Survey, High Cross, Madingley Road,

Cambridge CB3 0ET, UK

(ewwo@bas.ac.uk)

Why palaeo greenhouse gases?

• How do recent changes compare with natural variability?

• Can we understand natural cycles? – important if we want to underpin estimates of (future) feedbacks

• Does the past constrain the likelihood of “high impact, low probability” events (surprises)?

• How did Earth respond to high CO2 climates?• Can we find analogues for large carbon releases in

the past, to test effects and recovery?

Plan for today

• Set the scene by presenting the evidence

• Challenge the AIMES community to understand (at process level) the records

• Briefly consider which aspects of the past are most relevant to the future

• Muse on the extent to which the Quaternary Earth System was deterministic

Recent past – other GHG

240

280

320

1000 1200 1400 1600 1800 2000Age of air / years AD

N2O

/ pp

bv

0

600

1200

1800

CH

4 /

ppbv

280

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360

CO

2 /

ppm

v

Etheridge et al 1996MacFarling Meure et al 2006

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1000

1500

CH

4 /

pp

bv

250

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0200040006000800010000

South Pole flasksLaw Dome (Etheridge et al., 1996)Dome C ice (Fluckiger et al., 2002)

Age / years before 1950 AD

CO

2 /

pp

mv

Greenhouse gases over the Holocene (10 kyr)

Natural or anthropogenic?Ruddiman 2003 (Clim. Change, 61, 261-293)

European Project for Ice Coring in Antarctica (EPICA)

Dome C75ºS; 3233 m aslMean T:-54.5ºCCore to 3270 m

0km 1 ,000km 2 ,000km

80S°

70S°

60S°

Vo sto k

Do m e F

Ta ylo rDo m e

Byrd

Dro nn ingM a ud La nd

Sip le Do m e

Do m e CLa w Do m e

Be rkne rIsla nd

-10

-5

0

5

0 200 400 600 800

Age / thousands of years before present

Est

imat

ed D

ome

C

tem

pera

ture

diff

eren

ce / C

Estimated Antarctic temperature(based on water isotopes)

EPICA Community Members, Nature, 429, 623-628, 2004;Jouzel et al., Science, 2007

What does CO2 do in a changing climate?

- CO2 responsible for 30-50% of the glacial-interglacial warming- probably controlled mainly through processes in the Southern Ocean

200

250

300Lüthi et al., 2008

CO

2 / p

pmv

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-5

0

5

0 200 400 600 800Age / EDC3 ka bp (1950)

Est

imat

ed

Dom

e C

te

mpe

ratu

re d

iffer

enc

e / C

CO2 in the last glacial

Ahn and Brook 2008

Dome C detailed CO2

Monnin et al (2001)

Science 291, 112-114

Phasing is consistent with CO2 as an amplifier

13CO2

Lourantou et al, GBC, In Press (2010)

Estimates courtesy of Andy Ridgwell

But we are out of the range of the last 800 ka

150

200

250

300

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400

0 200 400 600 800Age / ka (b1950)

CO

2 /

pp

mv

Lüthi et al., Nature 2008 (EPICA gas consortium)

• In rate as well as concentration:– Fastest multicentennial rate in last termination was ~20 ppmv in

1000 years

– 20 ppmv increase in last 11 years

CH4

-450

-430

-410

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-370

0 200 400 600 800

Jouzel et al 2007

9C

COLD

WARM

Age / EDC3 ka before present

D /

‰

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1730

Loulergue et al, 2008, Nature

CH

4 /

ppbv

But the late Pleistocene holds no analogue for the present

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-370

0 200 400 600 800

Jouzel et al 2007

9C

COLD

WARM

Age / EDC3 ka before present

D /

‰

600

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1800

Loulergue et al, 2008, Nature

CH

4 /

ppbv

And natural changes are dwarfed by the anthropogenic influence

Rapid events in CH4

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700

10 20 30 40 50 60 70Age / ka b2k, converted to GICC05

CH

4 /

ppbv

-45

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-35

198

18O

/ ‰

Gre

enla

nd

tem

pera

ture

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Vostok + Dome C data

Age / kyr BP

CH

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pp

bv

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GRIP/NGRIP

Age / GICC05 yrs BP

CH

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pp

bv

Methane: the rapid jumps account for much of the g-ig change

Causes of change (CH4)

Sources• Wetlands

– Northern– Tropical

• Methane hydrates• Biomass burning• Others (vegetation,….)

Sinks• OH change

• Temperature• Water vapour• Competition

(VOCs)

Isotopic evidence suggests no major role for hydrates

δD of CH4Sowers, Science

2006Concludes marine clathrates are not important for these warming events

No evidence of fossil 14C at transitionLarge blocks from Pakitsoq, Greenland. Petrenko et al., 2009, Science

3-box modelDallenbach et al, GRL, 2000

Combining Dallenbach et al (GRL 2000) and Brook et al (GBC 2000), you would conclude:

Interhemispheric differences

Tropics North

DO cold-warm

Bolling/Allerod to YD

LGM to preBoreal

13CH4 - termination ILGM 13CH4 ~3.5 ‰ heavier than Holocene

rapid 13CH4 variations during Bolling/Alleroed -Younger Dryas

also slow changes during LGM and early Holocene when CH4 constant

D 20 ‰ heavier in LGM (Sowers, 2006)

Data not really in agreement with conclusions of Schaefer et al (2006)

Fischer et al., Nature 452, 864 (2008)

Glacial/interglacial CH4 source changes

10 Variables:

5(6) potenial preindustrial sources with different isotopic signature

1 atmospheric lifetime

3 different sinks with different contributions

4 Constraints:

CH4 concentration North & South

D(CH4) North

13CH4 South

Isotopic constraints

• Box model to estimate range of likely emissions and lifetimes in different time periods

• Relatively minor changes in isotopic content suggest changes in hydrates and biomass burning emissions were modest

• Concludes that main changes are in boreal wetlands and in atmospheric lifetime

• But conclusion on biomass burning seems at odds with terrestrial evidence and lifetime changes are hard to explain (see Levine talk)

• Also the wetland response seems stronger than bottom-up models would predict

Last interglacial – how did CH4 react to Arctic warmth?

-420

-390

EPICA Dome C

D /

‰

-45

-40

-35

0 50 100 150

NGRIP

Age / ka b1950

18O

/ ‰

300

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600

700

CH

4 /

pp

bv

Summary• Ice cores show us the unprecedented extent and

rate of the recent increase in greenhouse gases and therefore radiative forcing

• Large changes in Quaternary challenge us to understand natural cycles and test our knowledge of feedbacks (especially wrt ocean carbon and wetland methane)

• Last interglacial might be used to seek reassurance against large methane releases under warming

• For anything approaching an analogue for a world with higher CO2 we will have to tackle the harder questions posed by older climates

How deterministic is this system?

400

600

800 Loulergue et al 2008

CH

4 /

ppb

v

200

250

300Luethi et al 2008

CO

2 /

ppm

v

-440

-410

-380

0 200 400 600 800

Jouzel et al 2007

9C

COLD

WARM

Age / EDC3 ka before present

D /

‰

Thank you