Pioneering NASA climatologist James Hansen, one of the first scientists to raise the alarm about global warming, is retiring after 46 years, a colleague confirmed to AFP on Tuesday.
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.
Explore further: Unsafe levels of toxic pollutants in heavily fracked Ohio county