Aerosols influence Earth's shortwave radiation budget by scattering and absorbing radiation and by modifying the microphysical properties of clouds and in turn their reflectance and persistence. Over the industrial period concentrations of particulate substances in the troposphere have increased substantially on account of emissions from industrial activities--sulfur and nitrogen oxides from fossil fuel combustion, organics from fossil fuel and biomass combustion, agricultural burning and the like, and mineral dust from disturbed soils. Together these aerosols are thought to have decreased planetary absorption of solar radiation by an amount comparable to increased downwelling thermal infrared radiation due to increased concentrations of carbon dioxide and other "greenhouse" gases, offsetting much of the radiative forcing by these gases. However the aerosol influence is quite uncertain. This uncertainty greatly limits present ability to empirically infer Earth's climate sensitivity or to evaluate the accuracy of model simulations of climate change over the industrial period.
This page was last updated 2005-02-05.
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