The Climatic Effects of Ozone and Trace Gases

Summary

The climatic effects of a large number (>20) of trace gases, many of which have not been considered in previous investigations, are investigated. Using a one-dimensional radiative convective model the climatic impact of these gases is studied for three cases. First, using present day gas concentrations and growth rates, the effect of these gases on the equilibrium thermal structure 50 years from now is estimated. Secondly, pre-industrial gas concentrations are used to estimate climatic effects which should already have taken place. Finally, the relative importance for individual gases is calculated for a uniform 0 to 1 ppbv increase in gas concentration. The results of these calculations are: i) Increases in C0₂ from pre-industrial times (1850) to the present cause an increase in equilibrium surface temperature of 0.5 K. This effect due to C0₂ alone is amplified by a factor of 1.5 due to trace gases, ii) Increases in C0₂ from present concentrations to their expected levels 50 years from now result in an increase in equilibrium surface temperature of 0.7 K. The inclusion of all other trace gases enhances this increase by a factor of 2.0. The uncertainties in this factor due to uncertainties in gas concentrations is a change in enhancement from 1.5 to 3.0. iii) A number of trace gases have been identified which are of potential climatic importance based on a per ppbv increase in concentration; among these are CFC-13, 22, 116, CHF₃ and CH₂F₂. The surface temperature effects, on a per ppbv basis, of these gases are of similar magnitude to those due to CFC11 and 12. Comparison of the present results with previous studies is also made; and sources of differences are discussed. The results of this study are discussed in much greater detail in Ramanathan et al.(1984).