Radiative Forcing The balance between incoming solar radiation and heat radiation leaving the atmosphere.
Key Findings Extremely likely(> 95%) that humans have exerted a substantial warming influence on climate since 1750. Likely(> 66%) that the human influence by radiative forcing is at least 5 times greater than solar influence since 1750. Exceptionally unlikely(> 99%) that solar + volcanic radiative forcing for 1950-2005 was comparable to anthropogenic radiative forcing.
Major Types of Radiative Forcings Changes in … • Greenhouse Gases • Aerosols (particles) • Surface albedo • Contrails • Solar variability • Volcanic activity
Our Variable Star • Changes of ~ 0.2% (= 2.7 W m-2) reflect 11-year sunspot cycle
Radiative Forcing: Balanced State Radiative Balance Radiative-Dynamic Balance
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
Carbon Dioxide (CO2) Pre-industrial: ~ 280 ppm Sources: Fossil fuels Cement production Deforestation Biomass burning
CO2 Emissions O2 as CO2 : Combustion Plant respiration/photosynthesis 13C/12C: Atmosphere > Terrestrial Sources
Methane (CH4) • Sources: • Biogenic: • Wetlands • Rice • Biomass burning • Ruminants • Fossil fuel mining & distribution • Living vegetation? NOAA Global Monitoring Division (GMD) Advanced Global Atmospheric Gases Experiments (AGAGE) Mt. Pinatubo? Warm 1998? Economic Incentives?
Nitrous Oxide (N2O) • Sources: • Coastal areas: • continental shelves • estuaries • rivers • Land processes
Halocarbons Small amounts, but effective absorbers of infrared radiation Factors: Industrial processes Partly regulated by Montreal Protocol
Other Gases Stratospheric Ozone Tropospheric Ozone Stratospheric Water Vapor
Aerosol Types Sulphate Organic Carbon from Fossil Fuels Black Carbon from Fossil Fuels Biomass Burning Nitrate Mineral Dust
Aerosol Distributions Optical Depth: Radiative Thickness” Biomass Burning Mineral Dust Industrial Sea Salt White: measurement not possible
Land Use Changes Albedo Differences Forest < Cropland Snow-covered forest < Snow-covered cropland
Other Surface Effects Black Carbon on Snow/Ice Land-Use Changes on Surface Fluxes Anthropogenic Water Vapor Release Anthropogenic Energy Release CO2 Influence on Plant Physiology
Solar Heating: Change Variability due to 1. Changes in sunspots and faculae 2. Changes in solar diameter?