John Fialka says that the IPCC report was too optimistic:
Global-Warming Report Gets U.S. Emphasis - WSJ.com: U.S. government scientists Friday said the long-term outlook for global warming may be more dire than suggested by this week's United Nations' report, which they say doesn't fully address the impact of clouds and melting glaciers. Recent evidence of accelerated melting of glaciers in Greenland and the Antarctic ice cap came too late to be included in the report released Thursday by the U.N.-sponsored Intergovernmental Panel on Climate Change.
Glaciers are among the largest sources of fresh water in the world and are contributing to rising ocean levels. Rising sea levels could expose population centers bordering the ocean to more storm damage and could require evacuation in some areas. But the computer models used for the IPCC report based their predictions only on the results of heating of the existing water in the world's oceans, causing the oceans to expand and sea levels to rise, said Tom Delworth, a climate modeler for the National Oceanic and Atmospheric Administration, the government agency in charge of climate science and weather service.
The IPCC report predicts sea levels will rise by between one to two feet over the next 100 years. Mr. Delworth said there remains "much more uncertainty" over how much accelerated melting of glaciers might add to that.
A second area of continuing uncertainty has to do with the impact of clouds on climate change.... [T]he supercomputers the agency uses to model the effect on the earth's climate -- which were also used for the IPCC report -- aren't detailed or fast enough to predict how much clouds are accelerating the problem...