James Hansen is an American climate scientist known for his work on climate change and its impacts. He gained prominence in the 1980s when he testified before the U.S. Congress about the dangers of global warming. Hansen's research has focused on the effects of greenhouse gases, particularly carbon dioxide, on the Earth's climate. Hansen served as the director of the Goddard Institute for Space Studies at NASA for over three decades. He has authored numerous scientific papers and books, advocating for urgent action to address climate change. His efforts have made him a prominent figure in the global climate movement.