Hansen, 72, who headed the Goddard Institute for Space Studies in New York, announced his departure in an email to the New York Times on Monday.

The Times reported Hansen was stepping down to allow himself to campaign more aggressively for legislation to cut greenhouse gases.

Hansen first rose to prominence in 1988 when his testimony at a highly publicized US Congressional hearing thrust the issue of man-made climate change onto the political agenda.

His work has often been attacked by climate change skeptics while his activism has also brought him into conflict with the federal government, most notably when the administration of George W. Bush sought to muzzle him in 2005.

Gavin Schmidt, deputy chief of the Goddard Institute, was quoted as saying that Hansen "has been at the forefront of almost every conceptual advance in climate in science over 40 years."

"The stuff that Jim wrote 20 years ago has set the tone for the whole field [and the] predictions he made have generally worked out very favorably," Schmidt said.

Republicans favor action on climate change
Fairfax, Va. (UPI) Apr 2, 2013 - A majority of Republicans in the United States think America should take steps to address climate change, a poll indicates.

In the poll conducted by the Center for Climate Change Communication at George Mason University, 62 percent of Republicans and Republican-leaning Independents said they feel action is necessary to deal with climate change.

The survey conducted in January polled more than 700 people who self-identified as Republicans and Republican-leaning Independents about energy and climate change, a university release reported Tuesday.

"Over the past few years, our surveys have shown that a growing number of Republicans want to see Congress do more to address climate change," Mason Professor Edward Maibach said. "In this survey, we asked a broader set of questions to see if we could better understand how Republicans, and Independents who have a tendency to vote Republican, think about America's energy and climate change situation."

Respondents, by a 2 to 1 margin, said America should take action to reduce its fossil fuel use and that the benefits of clean energy outweigh the costs of increased government regulation or higher energy prices.

Only a third of respondents said they agreed with the Republican Party's present position on climate issues.

"The findings from this survey suggest there is considerable support among conservatives for accelerating the transition away from fossil fuels and toward clean renewable forms of energy, and for taking steps to address climate change," Maibach said.

"Perhaps the most surprising finding, however, is how few of our survey respondents agreed with the Republican Party's current position on climate change."

The poll was conducted between Jan. 12 and Jan. 27, with an average margin of error of plus or minus 4 percentage points.