Climate implications of the observed changes in ozone vertical distribution

Abstract

Satellite and ozone-sonde observations indicated a decreasing trend in the ozone concentration in the lower stratosphere and an increasing trend in the troposphere, especially the upper troposphere. We have used a one-dimensional radiative - convective model (RCM) to examine the climate implications of these observed changes in vertical distribution of ozone. Instantaneous radiative forcing calculated by the one-dimensional radiative transfer model indicated a net warming of the surface-troposphere system due to stratospheric ozone losses. The increase in tropospheric ozone causes an additional positive forcing. However, the radiative forcing due to increases in trace gases during the same period is larger than the forcing due to ozone changes. There is marked decrease of the instantaneous solar and longwave heating rates in the lower stratosphere due to stratospheric ozone losses. Increases in tropospheric ozone causes additional decrease in longwave heating rate, in the lower stratosphere. Consistent with the changes in the heating rates, the equilibrium temperature profile computed by the radiative-convective model predicted a cooling in the stratosphere of the order of 0-6°C and a very slight warming in the troposphere. The increase of tropospheric ozone causes an additional cooling in the stratosphere. The temperature decrease caused by ozone decrease in the lower stratosphere is larger than that caused by increase of trace gases concentration during the same period. The stratospheric cooling effect due to trace gases is, however, better presented near 30 km altitude.