1. Pleistocene + Modern Climate

2. Current grade scale

3. Where we are in Geologic time

4. Changes in surface ocean temperature –recorded in the O 18 /O 16 ratio in the shells of planktonic foraminifera –provide data about climatic events Ceonzoic climate has fluctuated

5. Oxygen Isotope Ratio

6. Why the Icehouse? Long-term climate drivers: –Plate tectonics Opening/closing of seaways –Ocean currents are our heat and AC Uplift and erosion of mountains –Weathering reduces atmospheric CO2 –Life: catastrophic evolution of new capabilities –O2 –Astronomical drivers Other bodies (moon, sun) pull on the Earth, changing its distance to the sun

7. Why the Pleistocene Icehouse ? Long-term tectonic driver: –Redirection of ocean currents: Isolation of Antarctica Collision of N and S America –New mountains = more weathering Mineral weathering reduces atmospheric CO2 less CO2 = less greenhouse effect

8. Antarctica became isolated: – ocean circulation changes, cools

9. Shut off E/W global ocean flow Isthmus of Panama: North & South American plates collided ~ 3.5 Ma Why the Icehouse?

10. Closing of Panama canal created Gulf Stream bringing warm moist water N Glaciers need precipitation

11. Cenozoic cooling is here

12. Expanded out: You are here

13. Put forth by the Serbian astronomer –Milutin Milankovitch while interned by Austro- Hungarians during WWI Minor irregularities in Earth's rotation and orbit –are sufficient to alter the amount of solar radiation that Earth receives at 65° N –and hence can change climate –(criticism at the time: why 65° N?!?) The Milankovitch Theory

14. Three Variables about 100,000 years Ellipticity

15. The angle between –Earth's axis –and a line perpendicular to the plane of its orbit around the Sun This angle shifts about 1.5° –from its current value of 23.5° –during a 41,000-year cycle Axis Tilt

16. Earth moves around the Sun –spinning on its axis –which is tilted at 23.5° to the plane of its orbit Earth’s axis of rotation –slowly moves –and traces out the path of a cone in space Precession Plane of Earth’s Orbit

17. At present, Earth is closer to the Sun in January In about 11,000 years, closer to the Sun in July Effects of Precession

18. Why sensitive to insolation at 65° N?

19. Ice-albedo feedback Albedo: the reflectivity of a surface –Percent reflected light/total incoming light

20. Ice-albedo feedback http://www.atmo.arizona.edu/students/courselinks/spring05/atmo336/lectures/sec5/iceage.html

21. Climate: atmospheric composition

22. What makes a greenhouse gas? A greenhouse gas transmits light, but absorbs or emits infrared radiation (heat)

23. Glass is a solid with greenhouse properties Closed car windows + black leather seats in August….

24. Current greenhouses Mars: background +5°C Earth: background + 33°C Venus: background +500 °C!

25. Water vapor is a climate feedback; CO2 is a greenhouse driver Water vapor is close to condensation point: –Earth T goes up --> more water vapor –Earth T goes down --> less water vapor

26. CO2 through the Pleistocene http://www.earthsky.com/shows/profiles/alley.php

28. Last 100 years

29. Stability and instability of the climate system: the Younger Dryas

30. Earth system hiccupped coming out of the last glaciation

31. Oceanic conveyor http://www.clivar.org/publications/other_pubs/clivar_transp/powerpoint_fig/conveyer_new.gif

32. Lake Agassiz collapse WS Broecker, Fossil fuel CO2 and the Angry Climate Beast, 2004

33. Oceanic conveyor http://www.clivar.org/publications/other_pubs/clivar_transp/powerpoint_fig/conveyer_new.gif

34. Last 100 years

35. Modern atmospheric CO 2

36. Atmospheric CO 2 sources NET Fossil fuel combustion: 6x10 9 tons/year NET biosphere: ZERO –Gross biosphere: 60x10 9 tons/year in and out will CO 2 make trees grow faster? –A little, but not enough to bail us out. –Especially if we keep cutting them down!

37. Current climate trends

39. What’s the future?