RADIATIVE FORCING OF THE EARTHS CLIMATE SYSTEM DUE TO TROPICAL TROPOSPHERIC OZONE PRODUCTION

The radiative forcing of the Earth's climate system due to tropical tr opospheric ozone is estimated using ozonesonde profiles and maps of th e tropospheric ozone column derived from satellite data. The forcing i s estimated using several different techniques in order to place bound s on its likely magnitude and to elucidate the role of biomass burning in producing the observed forcing. The results suggest that a widespr ead radiative forcing of at least 0.5 to 1 W m(-2) exists over large a reas in the tropics for much of the year. This radiative forcing is co mparable in magnitude, but opposite in sign, to estimates of the aeros ol forcing from tropical biomass burning. However, the burning contrib ution to ozone forcing is present over a larger geographic area than t he aerosol forcing. The majority of the burning and thus these radiati ve forcings have likely been present only in the past century. These e nhancements in tropical ozone are also estimated to be responsible for a radiative forcing of between 0.1 and 0.4 W m(-2) when globally aver aged. Comparison of these regional and global forcings due to tropical ozone changes to the estimates of forcing due to carbon dioxide and o ther trace gas increases since preindustrial times (about 2.45 W m(-2) ) suggests that the effects of tropical ozone changes could be signifi cant for evaluation of both regional and global anthropogenic forcing of climate.