A one-dimensional study of possible cirrus cloud feedbacks

Abstract

A standard radiative-convective model with high vertical resolution (10-mb grid spacing in the upper troposphere) is used to investigate some of these feedbacks in response to changes in atmospheric carbon dioxide concentration. It is shown that such a high resolution (or, indeed, an even higher resolution) may be necessary to resolve the change in tropopause height following a doubling of carbon dioxide. The cirrus cloud is allowed to adjust its height and ice water content in response to the warming, and experiments are repeated: 1) for fixed and moist adiabatic lapse rates, 2) with and without a prescribed relative humidity feedback, 3) at low as well as high vertical resolution, and 4) with the inclusion of a simple correction to account for the uncertain number of small ice crystals in cirrus clouds. The results imply that models with a coarse vertical resolution may be unable to capture small changes in cloud position that could substantially affect the overall strength of cirrus cloud feedbacks. -from Authors