and how cloud cover responds to an increase in global temperature.
Using the UN/IPCC measures, Mann says global temperatures increasing through the last century, And the UN/IPCC GCM's say:
3) The models predict that cloud cover should be decreasing, and, in fact, such a decrease is crucial to amplify the greenhouse effect so it becomes the "enhanced" greenhouse effect. All measurements show cloud cover is increasing. ***
3) The models predict that cloud cover should be decreasing, and, in fact, such a decrease is crucial to amplify the greenhouse effect so it becomes the "enhanced" greenhouse effect. All measurements show cloud cover is increasing. ***
I did a quick Web search.
From What happens if we double CO2 in a climate model? (from the United Nations Framework Convention on Climate Change site)
"In most models cloud cover increases in a warmer climate. This affects the energy budget in two opposing ways. Clouds reflect sunlight, reducing the amount of energy reaching the surface. They also act as a "blanket", reducing the earth's energy losses to space. As the total cloud cover increases, the first effect acts to reduce the warming (a negative feedback) while the second effect acts to increase it (positive feedback). Clouds are a major source of uncertainty. If clouds are allowed to change (and changes in sea-ice are suppressed), different climate models give answers ranging from 1.5 to 4.5 C for the warming due to doubling CO2. If the effects of cloud feedbacks are eliminated, this range is reduced to 1.7-2.3 C."
It's old (dated 1993). Did the models change that much in four years that "most" of them predict the opposite of what they predicted in 1993? That's hard for me to believe.
Look at figure 1 in this PDF paper:
Cloud representation in climate models:
It shows 10 models responding to a doubling of CO2. Five models show a decrease in top-of-the-atmosphere cloud radiative forcing, five show an increase. (The increases predicted are greater than the decreases, in general.) I'm not sure how increase or decrease in radiative forcing translates to increase or decrease in actual cloud cover, but clearly there's no majority agreement in the models!
So this quick survey indicates to me that point 3 is questionable. If you can find some additional support for the statement of that point, feel free. But as it stands it doesn't appear to reflect the state-of-the-science.
More next week.