1. VII. Climate Change Blackbody model Windows and saturation Feedbacks Aerosols

2. Blackbody model Energy In = Energy Out Energy In = 1368 W/m 2  Earth cross-section  (1-reflectivity) Energy Out = Earth surface Area   SB  T earth 4  SB is Stefan-Boltzmann constant T earth = 255 K ignores clouds and greenhouse gases

3. Energy Balance beyond Blackbody

4. Earth’s IR Emissions

5. Energy Balance beyond Blackbody

6. CO 2 Concentration increasing, seasonal variation Absorptions are nearly saturated

7. Saturation Strong CO 2 absorptions almost saturated. Window regions between strong absorbances: Activity: model greenhouse gases X and Y a) Consider [Y] = 2.5 x 10 13 molecules cm -3 at 1 in IR,  Y = 1 x 10 -19 cm 2 molecule -1 What is A( 1 ), the absorbance at 1 ? b) Add [X] = 2.5 x 10 11 molecules cm -3 at 1 in IR,  X = 4 x 10 -18 cm 2 molecule -1 at 2 in IR,  X = 1 x 10 -18 cm 2 molecule -1 What is the total A( 1 ) and what is A( 2 ) ? c) Does the addition of X reduce heat emission more at 1 or 2 ?

8. Global mean radiative forcing of climate for year 2000 relative to 1750 (IPCC) Human Affects on Radiation Budget

9. Greenhouse Gases See Coursepack Section E Table 3 Seinfeld and Pandis Figures 21.17-19 Instantaneouse Radiative Forcing (IRF) of a compound (Watts m -2 kg -1 ) Absolute Global Warming Potential (W m -2 kg -1 yr)

10. Greenhouse Gases Global Warming Potential (w/respect to CO 2 ) (dimensionless)

11. Key Points Radiative balance is complicated Greenhouse Gas effect real, global Greenhouse Gas effects not isolated - feedbacks with biosphere - feedback with geosphere Aerosol effects messy, local (temporary) Climatic effects hard to see (weather)