 External Causes Change in incoming radiation Change in composition of the atmosphere Change in Earth’s surface  Feedback Mechanisms Water vapor-greenhouse gas feedback (+) Snow-albedo feedback (+) Infrared radiation (-)

Big Picture Global Temp  Time (Mybp)  Eocene Oligocene Miocene Pleistocene Pliocene KT 60-70% loss of species COOLING

Pleistocene climate: highly variable ~23 ice ages ~40Kyr ~100kyr

41Kyr cycle

100kyr cycle

Causes of Climate Change  Plate Tectonics and Mountain Building Theory of plate tectonics Ridge and subduction Mountain interaction with airflow and ocean currents  Variation on the Earth’s Orbit Milankovitch Theory ○ Eccentricity ○ Precession ○ Obliquity

Pleistocene climate: highly variable ~23 ice ages ~40Kyr ~100kyr

Past 700,000 years: Ice cores 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 (CO 2 – Temp Feedback) Wisconsin Great Glaciation Covered all but the highest summits of the Rockies Temperature  CO 2 

Greenland Ice Core showing last ice age Ramstorf, Nature, 419, ,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

Younger Dryas Camp Century (Greenland) d 18 O record Boyle & Keigwin, 1987 see c_nl_2000_1.html YD Temperature   Time    Alley et al., o f in 5 years!!

Black Sea flooding Straits of Bosphorus began to leak around 5550 BC Many 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 11 th 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) ood html Straits as shallow as 36m!

African paleoclimate last 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

Greenland climate history  s: 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 ~ s 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. org/online/features/gree nland/

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

Global Warming  Recent Global Warming: Perspective Since the beginning of the 20 th century average global surface temperature has increase 0.8ºC  Radiative Forcing Agents Carbon dioxide and other greenhouse gases disrupt radiative equilibrium, forming an increase in temperature

Changing SST Linear trend

What the models show

Global Warming  Future Global Warming: Projections Double carbon dioxide levels will cause a surface warming of 2-4.5ºC Uncertainties: ○ The effect of water and land on rising levels of carbon dioxide ○ Amount or greenhouse gases Question of Clouds ○ Clouds reflect radiation and emit infrared radiation, positive and negative feedbacks.