The role of atmospheric chemistry in climate change

Surface emissions and concentrations of globally important trace gases are increasing. Climate models indicate significant temperature increases could occur in the next century due to increasing CO₂concentrations. However, the combined direct radiative effects from other trace gases could be as large as those estimated for CO₂. Many of these gases also have indirect effects on climate through their chemical interactions with other.radiatively important atmospheric constituents. For example, within the troposphere, emissions of CH₄, CO, and NO_xmay increase concentrations of ozone, an important radiatively active gas. These emissions may also affect concentrations of hydroxyl (OH), which, while not radiatively important, has an important impact on tropospheric chemistry and on the concentrations of long-lived gases reaching the stratosphere. In the stratosphere, dissociation of CH₄, N₂O, and the CFCs can lead to changes in the ozone distribution. Oxidation of increasing CH₄concentrations would increase stratospheric concentrations of radiatively important water vapor. Climate change can, on the other hand, alter tropospheric H₂O concentrations, further affecting chemistry impacts on climate. In this paper, we examine the importance of chemical processes and other interactions in determining climatic change and future policy options.