Role of Aerosols in Radiative Forcing of Climate Change: Global Mean and Uncertainties

Anthropogenically induced climate change is of great current interest because of increases in atmospheric loading of infrared active (greenhouse) gases over the past 150 years and the inferred resultant increase in infrared radiation flux in the troposphere. However the climate change ascribed to such increases, not to mention predictions of future climate change in response to prospective changes in the earth's radiation budget, is based virtually entirely on climate model simulations of how the earth's climate would respond to changes in radiation rather than on empirically established relationships between changes in the earth's radiation budget and climate change. There is thus an urgent need to evaluate the performance of climate models to ascertain the accuracy with which they represent the changes in temperature and other indicia of climate that have been observed over the industrial period. Such an evaluation, however, requires an accurate assessment of the totality of changes in the earth's radiation budget in both the longwave (thermal infrared) and shortwave (solar) spectral regions, not just of changes in the longwave due to increased concentrations of long-lived greenhouse gases. Changes in downwelling thermal infrared radiation arise from changes in tropospheric an