In the New York Times:

A top NASA climate expert who twice briefed Vice President Dick Cheney on global warming plans to criticize the administration's approach to the issue in a lecture at the University of Iowa tonight and say that a senior administration official told him last year not to discuss dangerous consequences of rising temperatures.

The expert, Dr. James E. Hansen, director of the NASA Goddard Institute for Space Studies in Manhattan, expects to say that the Bush administration has ignored growing evidence that sea levels could rise significantly unless prompt action is taken to reduce heat-trapping emissions from smokestacks and tailpipes.

Many academic scientists, including dozens of Nobel laureates, have been criticizing the administration over its handling of climate change and other complex scientific issues. But Dr. Hansen, first in an interview with The New York Times a week ago and again in his planned lecture today, is the only leading scientist to speak out so publicly while still in the employ of the government.
<...>
In a draft of the talk, a copy of which Dr. Hansen provided to The Times yesterday, he wrote that President Bush's climate policy, which puts off consideration of binding cuts in such emissions until 2012, was likely to be too little too late.

Actions to curtail greenhouse-gas emissions "are not only feasible but make sense for other reasons, including our economic well-being and national security," Dr. Hansen wrote. "Delay of another decade, I argue, is a colossal risk."
<...>
Dr. Hansen, 63, acknowledged that he imperiled his credibility and perhaps his job by criticizing Mr. Bush's policies in the final days of a tight presidential campaign. He said he decided to speak out after months of deliberation because he was convinced the country needed to change course on climate policy.