Originally Posted by dawei
Does anyone know of a reputable source for the trend in low level cloud cover over the past few decades?
I found this and this, but neither seem very trustable.
Also, assuming the skeptics who use these graphs found them from some place more credible than their own toilets, why do IPCC radiative forcing estimates show clouds as a negative forcing when their overall extent is clearly decreasing?
I think that is the ISCCP data. If you google "ISCCP cloud cover trend" and similar strings you can find lots of information, and the primary data, on the web. Here is a relevant reference on the subject:
Title: Arguments against a physical long-term trend in global ISCCP cloud amounts
Author(s): Evan AT (Evan, Amato T.), Heidinger AK (Heidinger, Andrew K.), Vimont DJ (Vimont, Daniel J.)
Source: GEOPHYSICAL RESEARCH LETTERS Volume: 34 Issue: 4 Article Number: L04701 Published: FEB 17 2007
Abstract: The International Satellite Cloud Climatology Project (ISCCP) multi-decadal record of cloudiness exhibits a well-known global decrease in cloud amounts. This downward trend has recently been used to suggest widespread increases in surface solar heating, decreases in planetary albedo, and deficiencies in global climate models. Here we show that trends observed in the ISCCP data are satellite viewing geometry artifacts and are not related to physical changes in the atmosphere. Our results suggest that in its current form, the ISCCP data may not be appropriate for certain long-term global studies, especially those focused on trends.''