Cloud optical feedback and climate stability in a radiative-convective model

Abstract

A globally averaged, one-dimensional radiative-convective climate model is used to study the effect of clouds on both the climate and the sensitivity of climate to changes in incoming solar radiation. The model has been run with low, mid and high clouds of different areas, heights and liquid water contents (LWC). The cloud optics in both solar and terrestrial infrared wavelengths are a function of the cloud LWC.

In some runs the cloud properties are held fixed. Then the model temperature is strongly dependent upon the selected LWC of clouds, especially when the LWC is small. The model sensitivity to changes in the solar constant is not, however, so strongly dependent upon the selected cloud area, height, or LWC.

In other model runs the cloud LWCs are permitted to vary in direct proportion to the water vapor mixing ratio, which changes with temperature. This permits a rough evaluation of the feedback relations between cloud optical properties and climate. Under this hypothesis, variable cloud optics generally serve as a significant negative feedback mechanism in climate change. High thin cirrus can be a special positive feedback case.