On October 9 2009 I posted regarding a GEWEX presentation by Graeme Stephens in
A published version of his August presentation has appeared in the February 2010 GEWEX Newsletter. It is titled
Is There a Missing Low Cloud Feedback in Current Climate Models?
The article by Graeme is headlined on the front cover of the Newsletter with the text
“An analysis by Prof. Graeme Stephens in the article on page 5 suggests that solar radiation reflected by low
clouds is significantly enhanced in models compared to real cloud observations. This finding has major implications for the cloud-climate feedback problem in models.”
The summary of his findings include the text
“The net consequence of these biases is that the optical depth of low clouds in GCMs is more than a factor of two greater than observed, resulting in albedos of clouds that are too high.”
“The implication of this optical depth bias that owes its source to biases in both the LWP and particle sizes is that the solar
radiation reflected by low clouds is significantly enhanced in models compared to real clouds. This reflected sunlight bias
has significant implications for the cloud-climate feedback problem. The consequence is that this bias artificially
suppresses the low cloud optical depth feedback in models by almost a factor of four and thus its potential role as a negative feedback.”
This study further supports the finding that I reported early today that natural radiative forcings and feedbacks are more significant than concluded in the 2007 IPCC assessment.