The International Satellite Cloud Climatology Project (ISCCP) dataset is used to correlate variations of cloud optical thickness and cloud temperature in today's atmosphere. The analysis focuses on low and cirrus clouds. Cold low clouds show increases in cloud optical thickness with temperature consistent with adiabatic behavior, while warm low clouds primarily show decreases in cloud optical thickness with temperature. An exception are subtropical low clouds which show a tendency for increases in optical thicknesses with temperature, particularly during El Ni¿o years. High and middle latitude cirrus clouds show increases in optical thickness with temperature. In subtropical and tropical latitudes, cirrus cloud optical thicknesses show a complicated behavior that could be related to changes in the dynamical regime in which the clouds are formed. ¿ American Geophysical Union 1994