External Causes Change in incoming radiation Change in composition of the atmosphere Change in Earth’s surface Feedback

1. 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 (-)

2. Big Picture KT 60-70% loss of species Pliocene Pleistocene Eocene Oligocene Miocene COOLING Global Temp  65 55 34 24 5.4 1.8 Time (Mybp) 

3. Pleistocene climate: highly variable ~23 ice ages ~40Kyr ~100kyr http://uregina.ca/~radenbat/envgeol/glaciers/Iceages_climatechange.html

4. 41Kyr cycle

5. 100kyr cycle

6. 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

7. Pleistocene climate: highly variable ~23 ice ages ~40Kyr ~100kyr http://uregina.ca/~radenbat/envgeol/glaciers/Iceages_climatechange.html

8. Past 700,000 years: Ice cores Ice core being extracted At Vostok 3.4km ice http://www.ngdc.noaa.gov/paleo/slides/slideset/20/20_406_slide.html Annual dust layers in GISP2

9. Antarctic Ice core showing last 4 ice ages(CO2 – Temp Feedback) Wisconsin CO2 Temperature  Great Glaciation Covered all but the highest summits of the Rockies http://www.ipcc.ch/pub/tar/wg1/fig2-22.htm

10. Greenland Ice Coreshowing last ice age • Dansgaard/Oeschger events : warm • Heinrich events: ice-rafting stage 3 D/O warm events Time (kyr)  Heinrich ice/cool events Ramstorf, Nature, 419, 207-213,2002.

11. Laurentide ice sheet and the Great Lakes http://www.uwgb.edu/dutchs/glkhist/glkhist0.htm

12. Younger DryasCamp Century (Greenland) d18O record -25of in 5 years!! YD   Temperature   Time 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 Alley et al., 1993 http://www.pbs.org/wgbh/nova/warnings/stories/

13. Black Sea floodingStraits 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 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) Straits as shallow as 36m! http://abcnews.go.com/sections/Science/DailyNews/flood000914.html http://www.robotwisdom.com/science/blacksea.html

15. African paleoclimatelast 15,000 years Massive Lake Chad • 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

16. 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

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

19. 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 14th C • Collapse of the ivory market due to African trade • 1721: Danes reestablish an outpost. http://www.archaeology.org/online/features/greenland/

20. A Frost Fair on the Thames at Temple Stairsby Abraham Hondius in 1684 Detail http://www.museumoflondon.org.uk

21. Global Warming • Recent Global Warming: Perspective • Since the beginning of the 20th 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

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

24. Changing SST Linear trend 1900 - 1991

25. What the models show

26. 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.