A STUDY OF GREENHOUSE EFFECTS USING ZERO, ONE AND TWO-DIMENSIONAL CLIMATE MODELS

Abstract

In this study a hierarchy of simple climate models is built and used to assess the impact of changes in the trace gas abundance of Earth's atmosphere on the global and zonal surface temperatures. Two of the four models presented use the Equivalent Radiative Atomosphere approximation to treat the greenhouse effect of water vapor, carbon dioxide and ozone. The other two models have vertically resolved atmospheres and use broad band absorptance and emissivity models in the treatment of radiative exchanges. Two of the models have resolution in the meridional direction and the horizontal energy transport is approximated by a linear, constant coefficient diffusion. A series of sensitivity experiments is conducted with these models to assess the relative importance of various parameters and modeling assumptions. All of the models are sensitive to variations in solar irradiance: the range of the response, quantified in terms of the (beta) parameter, ranges from 71 K to 186 K. The response is highly dependent on the strength of the water vapor feedback in the particular model. Another series of calculations is concerned with the impact of changes in the CO(,2) abundance of the atmosphere on the surface temperatures. The range of the response to a doubling of the CO(,2) abundance is from 2.5 K to 10 K for ERA based models and from 1.9 K to 6 K for the others. The response depends on the latitude and most importantly on the water vapor feedback strength. The effect of minor trace gases O(,3), CH(,4) and N(,2)O on the globally averaged temperature is also studied. A 50% decrease in O(,3) column density lowers the surface temperature by 0.28 K. A doubling of the present atmospheric abundance of CH(,4) and N(,2)O heats the surface by 0.25 K and 0.42 K, respectively