A global interactive chemistry and climate model: Formulation and testing

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Abstract
In order to elucidate interactions between climate change and biogeochemical processes and to provide a tool for comprehensive analysis of sensitivity, uncertainty, and proposed climate change mitigation policies, we have developed a zonally averaged two‐dimensional model including coupled biogeochemical and climate submodels, as a part of an integrated global system model. When driven with calculated or estimated trace gas emissions from both anthropogenic and natural sources, it is designed to simulate centennial‐scale evolution of many radiatively and chemically important tracers in the atmosphere. Predicted concentrations of chemical species in the chemistry submodel are used interactively to calculate radiative forcing in the climate submodel, which, in turn, provides winds, temperatures, and other variables to the chemistry submodel. Model predictions of the surface trends of several key species are close to observations over the past 10–20 years. Predicted vertical distributions of climate‐relevant species, as well as seasonal variations, are also in good agreement with observations. Runs of the model imply that if the current increasing trends of anthropogenic emissions of climate‐relevant gases are continued over the next century, the chemical composition of the atmosphere would be quite different in the year 2100 than that currently observed. The differences involve not only higher concentrations of major long‐lived trace gases such as CO2, N2O, and CH4 but also about 20% lower concentrations of the major tropospheric oxidizer (OH free radical), and almost double the current concentrations of the short‐lived air pollutants CO and NOx.