External CausesChange in incoming radiationChange in composition of the atmosphereChange in Earth’s surface

Feedback MechanismsWater vapor-greenhouse gas feedback (+)Snow-albedo feedback (+)Infrared radiation (-)

Big Picture

65 55 34 24 5.4 1.8

Glo

bal

Tem

p

Time (Mybp)

Eocene Oligocene Miocene

Pleis

toce

ne

Plio

cene

KT

60-7

0% lo

ss o

f

spec

ies

COOLING

Pleistocene climate: highly variable

http://uregina.ca/~radenbat/envgeol/glaciers/Iceages_climatechange.html

~23 ice ages

~40Kyr

~100kyr

41Kyr cycle

100kyr cycle

Causes of Climate Change

Plate Tectonics and Mountain BuildingTheory of plate tectonicsRidge and subductionMountain interaction with airflow and ocean

currents Variation on the Earth’s Orbit

Milankovitch Theory○ Eccentricity○ Precession○ Obliquity

Pleistocene climate: highly variable

http://uregina.ca/~radenbat/envgeol/glaciers/Iceages_climatechange.html

~23 ice ages

~40Kyr

~100kyr

Past 700,000 years: Ice cores

http://www.ngdc.noaa.gov/paleo/slides/slideset/20/20_406_slide.html

Ice core being extracted

Annual dust layers in GISP2

At Vostok 3.4km ice

Antarctic Ice core showing last 4 ice ages

(CO2 – Temp Feedback)

http://www.ipcc.ch/pub/tar/wg1/fig2-22.htm

Wis

con

sin

Gre

at G

laci

atio

nCovered all but the highest summits of the Rockies

T

emp

erat

ure

CO

2

Greenland Ice Coreshowing last ice age

Ramstorf, Nature, 419, 207-213,2002.

D/O warm events

Heinrich ice/cool events

•Dansgaard/Oeschger events : warm

•Heinrich events: ice-rafting

Time (kyr)

stage 3

Laurentide ice sheet and the Great Lakes

http://www.uwgb.edu/dutchs/glkhist/glkhist0.htm

Younger DryasCamp Century (Greenland) d18O record

Boyle & Keigwin, 1987 see http://www.doc.mmu.ac.uk/aric/gccsg/5-3-2-1.html, http://www.clivar.org/publications/exchanges/ex15/pc_nl_2000_1.html

YD

Te

mp

era

ture

Time

Alley et al., 1993http://www.pbs.org/wgbh/nova/warnings/stories/

-25of in 5 years!!

Black Sea flooding Straits of Bosphorus began to leak around 5550 BCMany middle eastern creation stories refer to a massive flood

Babylonian mythology (Ghilgamesh, a 12-tablet long saga discovered in a palace in Nineva. Flood is described on the 11th tablet. Copied from the 1,800BC Akkadian Atra-Hasis epic)

Egyptian mythology (out of Nu {Nun: watery chaos} Atum created a hill …) Greek mythology (following the opening of Pandora’s box …) Judao-Christian (Genesis 7:20: “…Fifteen cubits [7m] upward did the waters

prevail; and the mountains were covered.” King James)

http://www.robotwisdom.com/science/blacksea.htmlhttp://abcnews.go.com/sections/Science/DailyNews/flood000914.html

Straits as shallow as 36m!

African paleoclimatelast 15,000 years

15ky: Arid conditions. Sahara desert zone expanded: Rainforest changes to savanna (Thorp 1994)

10ky: likely in response to the shift of perihelion from July to Dec, Sahara shrank. Monsoon strengthened and expanded north and east. Lakes (e.g. Lake Chad) in the Sahara. Increasing Nile discharge deposited oxygen-rich

black muds (sapropels). 6.7ky: drier conditions began. (Nicholson and

Flohn, 1980) 4-3.6ky: brutal drought causes massive population

movement (Claussen et al., 1999). Akkadian empire collapses.

0ky: poor agricultural practices lead to further drop in water table and increasing salinity of ground water

Massive Lake Chad

Effect of expanded monsoon on northern Sahara (10ky)

Paleo-lake sediments contain organic material and mollusc shells. These paleo lakebeds are the source of much of the Saharan dust

African dust outbreak

http://science.nasa.gov/headlines/images/dust-quicky/dustmovie_big.gif

Greenland climate history

700-1100s: little sea ice was present to hinder navigation. 980s: Norse move from Iceland to Greenland led by Eirik Thorvaldsson

(known as Erik the Red), who was the father of Leif Eiriksson. Erik was escaping a death sentence for killing 2 guys in a fight.

1350: western settlement was abandoned 1408: eastern settlement was largely abandoned. A few persisted until

~1500. 1430s had particularly severe winters. 1492: “due to the severe freezing of the seas, no ship is believed to have

put in to land there for eighty years." (Letter from Pope Alexander VI ). But other factors included: Poor soil management Rise of the Hunseatic League shutting down Danish trading Greater opportunities further east, partly due to the plagues of the 14 th C Collapse of the ivory market due to African trade

1721: Danes reestablish an outpost.

http://www.archaeology.org/online/features/greenland/

A Frost Fair on the Thames at Temple Stairs by Abraham Hondius in 1684

http://www.museumoflondon.org.uk

Detail

Global Warming

Recent Global Warming: PerspectiveSince the beginning of the 20th century

average global surface temperature has increase 0.8ºC

Radiative Forcing AgentsCarbon dioxide and other greenhouse gases

disrupt radiative equilibrium, forming an increase in temperature

http://lwf.ncdc.noaa.gov/img/climate/research/trends/1901-annual-pg.gif

Changing SSTLinear trend 1900 - 1991

What the models show

Global Warming

Future Global Warming: ProjectionsDouble carbon dioxide levels will cause a

surface warming of 2-4.5ºCUncertainties:

○ The effect of water and land on rising levels of carbon dioxide

○ Amount or greenhouse gasesQuestion of Clouds

○ Clouds reflect radiation and emit infrared radiation, positive and negative feedbacks.