The nation’s leading climate scientist, Dr. James Hansen, is retiring after more than 40 years to focus on activism around fighting global warming. For over 25 years, Dr. Hansen has headed the Goddard Institute for Space Studies, NASA’s premiere climate research center. His testimony to a Senate committee in 1988 first brought the threat of global warming to the world’s attention. Under the George W. Bush administration, he went public to reveal the White House tried to silence his warnings about the urgent need to address climate change. He has since been arrested outside the White House for protesting mountaintop removal and the Keystone XL pipeline. Hansen says he now plans to devote his time to campaigning in the United States for the reduction of the greenhouse gases that cause global warming.