Response of the climate system to atmospheric aerosols and greenhouse gases

RECENTLY, Kiehl and Briegleb1 evaluated the radiative forcing associated with the capacity of atmospheric sulphate aerosols to reflect solar radiation back into space, and compared this with the forcing associated with atmospheric greenhouse gases. They found that the (negative) climate forcing by the aerosols has strong regional character, with the greatest forcing over Northern Hemisphere land surfaces, whereas the (positive) forcing by greenhouse gases is distributed almost equally between the hemispheres and varies mainly as a function of latitude. Here we present simulations of the response of the climate system to these two types of forcing. We find that the global response to aerosol forcing is regionally heterogeneous, with a distribution that is different from the forcing pattern. The simulations also imply that, for equal magnitudes of forcing, the temperature response is markedly greater for carbon dioxide than for aerosol forcing. We conclude that to predict the global mean climate response to global mean forcing, it is necessary to separate out the different components of the forcing to which the climate system is sensitive.