“Settled science would know all of the important “forcings” and “feedbacks” in the climate system, such as the sensitivity of surface temperature to changes in carbon dioxide (a forcing) and the behavior of clouds, which could either enhance or counter warming (a feedback).”
Pat Michaels comments at Forbes.com:
…Now it appears that cloud tops are lowering, a totally unforeseen cooling feedback on carbon dioxide-induced warming. Writing in Geophysical Research Letters, University of Auckland’s Roger Davies and Matthew Molloy conclude this could be a “significant measure of a negative cloud feedback to global warming”.
The average global cloud height is linked to the average global temperature—generally, the higher the average cloud height, the higher the average surface temperature, and vice versa. The tie-in is related to the height in the atmosphere from which clouds radiate infrared radiation to space. The higher up they are, the cooler they are, and they dissipate less radiation, which means the surface stays warmer.
Problem is that there’s only ten years of data, and there was a pretty decent La Nina (that’s the cold side of El Nino) in the Pacific Ocean in 2008, which was clearly correlated with a decline in cloud top height. Davies and Molloy are therefore properly cautious with their conclusions, but nonetheless note that a comparison of the beginning and endpoints for their study, which minimizes the La Nina contribution, still showed a decline in cloud height.
Who’d a thunk this one? Based upon data from the paper, the cooling climate impact from the decrease in the average global cloud height more than offset the positive forcing from an increase in greenhouse gases from human activities in the last decade…