1. 1 Radiative Forcing The balance between incoming solar radiation and heat radiation leaving the atmosphere.

2. 2 Key Findings 1.Extremely likely (> 95%) that humans have exerted a substantial warming influence on climate since 1750. 2.Likely (> 66%) that the human influence by radiative forcing is at least 5 times greater than solar influence since 1750. 3.Exceptionally unlikely (> 99%) that solar + volcanic radiative forcing for 1950-2005 was comparable to anthropogenic radiative forcing.

3. 3 Major Types of Radiative Forcings Changes in …  Greenhouse Gases  Aerosols (particles)  Surface albedo  Contrails  Solar variability  Volcanic activity

4. 4 Our Variable Star  Changes of ~ 0.2% (= 2.7 W m-2) reflect 11-year sunspot cycle

5. 5 Radiative Forcing: Balanced State Radiative Balance Radiative-Dynamic Balance

6. 6 Radiative Forcing Change in net radiative energy flux at the tropopause with … (a) stratospheric temperatures readjusted to radiative equilibrium (b) surface and tropospheric temperatures and state held fixed at original values

7. 7 Carbon Dioxide (CO 2 ) Pre-industrial: ~ 280 ppm Sources: 1.Fossil fuels 2.Cement production 3. Deforestation 4. Biomass burning

8. 8 CO 2 Emissions 13C/12C: Atmosphere > Terrestrial Sources O 2  as CO 2  : Combustion Plant respiration/photosynthesis

9. 9 Methane (CH 4 ) NOAA Global Monitoring Division (GMD) Advanced Global Atmospheric Gases Experiments (AGAGE) Sources: Biogenic: Wetlands Rice Biomass burning Ruminants Fossil fuel mining & distribution Living vegetation? Mt. Pinatubo? Economic Incentives? Warm 1998?

10. 10 Nitrous Oxide (N 2 O) Sources: Coastal areas: continental shelves estuaries rivers Land processes

11. 11 Halocarbons Small amounts, but effective absorbers of infrared radiation Factors: Industrial processes Partly regulated by Montreal Protocol

12. 12 Other Gases Stratospheric Ozone Tropospheric Ozone Stratospheric Water Vapor

13. 13 Aerosol Effects

14. 14 Aerosol Types Sulphate Organic Carbon from Fossil Fuels Black Carbon from Fossil Fuels Biomass Burning Nitrate Mineral Dust

15. Aerosol Distributions Biomass Burning Optical Depth: Radiative Thickness” Mineral Dust Industrial Sea Salt White: measurement not possible

16. Land Use Changes Albedo Differences Forest < Cropland Snow-covered forest < Snow-covered cropland

17. 17 Other Surface Effects Black Carbon on Snow/Ice Land-Use Changes on Surface Fluxes Anthropogenic Water Vapor Release Anthropogenic Energy Release CO 2 Influence on Plant Physiology

18. 18 Solar Heating: Change Variability due to 1. Changes in sunspots and faculae 2. Changes in solar diameter?

19. 19 Reconstructed Solar Heating

20. 20 Volcanic Aerosols

21. 21 Time Evolution of Forcing (Representative GCM)

22. Net RF: 1750 to 2005

23. 23 Changes in Radiative Forcing