Analyzing global trends of different cloud types and their potential impacts on climate by using the ISCCP D2 dataset

The International Satellite Cloud Climatology Project (ISCCP) D2 dataset is used to study the global distribution of low, middle and high cloud amounts and their trends of 1983-2001. Evidences have shown that global warming has accelerated over the past 20 a and the 1990s was the warmest decade in the instrumental records since 1861. Trends of various clouds amounts over this period are analyzed by employing the linear regression method. The results show that global mean total cloud amounts, in general, have tended to reduce over the past 20 a. But there are slightly increasing by about 2% before 1987 and decreasing by about 4% since then. Cloudiness trends of both low and high clouds decrease while increase for the middle cloud. And there exist remarkable discrepancies in different regions. The preliminary analyses suggest that it is likely that the cloud change occurring over the past 20 a is a positive feedback to global warming.