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.
As far as I can determine, the Holtz statement may have been rooted in a limited set of models as his chart of scoring results, refers to cloud cover being inconsistent among the models instead of generally one direction.
I'll go with Richard S. Lindzen's overall assessment(2000) of the GCM's as more representative the the current-state-of-the-science.
From Bulletin of the American Meteorological Society (March 2000) &
an interview with Tech Central Station (March 5, 2001, www.techcentralstation.com),
The biggest uncertainty in climate science is how feedbacks affect the climate. Global warming theory posits that a rise in atmospheric CO2 will only cause a slight warming of the atmosphere, on the order of about 1 degree centigrade. This small amount of warming, according to standard global warming theory, speeds up evaporation, increasing the amount of water vapor, the main greenhouse gas in the atmosphere. This positive feedback is where most of the predicted warming comes from.
A new study in the Bulletin of the American Meteorological Society (March 2000) shows that the reverse is true. The authors find a negative water vapor feedback effect that is powerful enough to offset all other positive feedbacks. Using detailed daily observations of cloud cover from satellites in the tropics and comparing them to sea surface temperatures, the researchers found that there is an "iris effect" in which higher temperatures reduce the warming effect of clouds.
According to a NASA press release about the study, "Clouds play a critical and complicated role in regulating the temperature of the Earth. Thick, bright, watery clouds like cumulus shield the atmosphere from incoming solar radiation by reflecting much of it back into space. Thin, icy cirrus clouds are poor sunshields but very efficient insulators that trap energy rising from the Earth’s warmed surface. A decrease in cirrus cloud area would have a cooling effect by allowing more heat energy, or infrared radiation, to leave the planet."
The researchers found that a one degree centigrade rise in ocean surface temperature decreased the ratio of cirrus cloud area to cumulus cloud area by 17 to 27 percent, allowing more heat to escape.
In an interview with Tech Central Station (March 5, 2001, www.techcentralstation.com), Dr. Richard S. Lindzen, the lead author, said that the climate models used in the IPCC have the cloud physics wrong. "We found that there were terrible errors about clouds in all the models, and that that will make it impossible to predict the climate sensitivity because the sensitivity of the models depends primarily on water vapor and clouds. Moreover, if clouds are wrong, there’s no way you can get water vapor right. They’re both intimately tied to each other." Lindzen argues that due to this new finding he doesn’t expect "much more than a degree warming and probably a lot less by 2100."
Does the Earth Have an Iris Analog?
Evidence Against the Iris Hypothesis
"Lin's team took the measurements made every day by CERES over the tropical oceans and plugged them into the same model that Lindzen used. Instead of the strong negative feedback that Lindzen's team found, Lin's team found a weak positive feedback (Lin et al. 2001). That is, Lin found that clouds in the tropics do change in response to warmer sea surface temperatures, but that the cloud changes serve to slightly enhance warming at the surface. Specifically, whereas Lindzen's experiment predicts that cirrus clouds change in extent to reduce warming at the surface by anywhere from 0.45 to 1.1 degrees, Lin's experiment predicts that changes in the tropical clouds will help warm the surface by anywhere from 0.05 to 0.1 degree (Lin et al. 2001)."
Reconciling the Differences (journal references are in this section)
Lindzen's a good scientist, and one of the best global warming skeptics currently active. Just because he's good doesn't mean that he's right all the time.
But you won't get much of an argument from me that the cloud feedback is still one of the great uncertainties in predictive climate modeling. I just wish that occasionally you'd acknowledge that the arguments from the skeptical side (such as Hoyt's scorecard assessments) won't always be right, too.
More today as time allows. I think that you've provided me with eight posts that I could respond to.