1. Evidence for Milankovitch theory (wikipedia!)

2. Px272 Lect 3: Forcing and feedback Balance of solar incoming, and earth emitted outgoing radiation Increments relative to pre-industrial era Assumption that solar incoming ~ constant. Change is made in surface temperature as a consequence of forcing. i.e. For a given radiative forcing we get a temperature change given by

3. Climate sensitivity

4. Figure TS.5 Anthropogenic Radiative Forcings IPCC AR4 2007

5. Aerosol direct forcing Nature 438, 1138 (Dec 2005)

6. Aerosol indirect forcing effect

7. Figure TS.5 Radiative Forcings IPCC AR4 2007

8. G/house gas and aerosol buildup Rise of global Greenhouse gases with industrial era ( IPCC S/PM 2001) CO2 emissions continue to accelerate (IPCC 2007)

9. IPCC 2007

10. (b) Sulphate aerosols deposited in Greenland ice Industrial sulphate aerosols appear to have peaked for Greenland record.

11. Global warming potentials (GWP): The ratio of the radiative forcing produced over a timescale of 100 years for 1kg of greenhouse gas, relative to 1kg of carbon dioxide. Greenhouse gasGWP Carbon dioxide (CO 2 )1 Methane (CH 4 )25 Nitrous Oxide (N 2 0)298 Hydrofluorocarbons (HFCs) 12-12000 Perfluorocarbons (PFCs) 5000-12000 Sulphur hexafluoride (SF 6 ) 22200 Houghton (2009)

12. Response and Feedback Add in some feedback Feedback can either amplify, or damp the impact of changes in forcing Positive feedback has positive f, negative feedback has negative f. Stability limit f<1 (some would claim this is exceeded). f defined as

13. Response and Feedback

14. Water vapour feedback Water saturation (mid troposphere) <-Simulation Observed->

15. Cloud Radiation Feedback Potentially quite large Altitude dependent Net highly uncertain

16. Ocean Circulation Feedback Huge heat capacity - delays warming Circulation driven by: temperature difference salinity difference rotation of earth - redistributes regionally: more winter heat to NW Europe from ocean transport than from sun - global heat redistribution still dominated by atmosphere

17. Ice Albedo Feedback

18. Arctic sea ice decrease

19. (ca 2002)

20. Changes in atmospheric composition 1990-2000 IPCC fig 3.4