# James Hansen James Hansen is an American climatologist who, more than any other single scientist, moved climate change from the laboratory into public and political consciousness. As director of NASA's Goddard Institute for Space Studies, he testified before the U.S. Senate on a sweltering day in June 1988 that he was "99% certain" the observed warming was not natural variability but the greenhouse signal emerging from the noise. The testimony, front-paged across the country, is widely treated as the moment global warming entered mainstream American politics. ## Scientific Contributions Hansen's research career predates his fame. He worked on the atmosphere of Venus — a natural laboratory for the runaway [[Greenhouse Effect]] — before turning to Earth. He was a pioneer of [[Climate Models]], and the projections he presented in 1988 have aged well: when compared against the emissions that actually occurred, his forecasts of warming proved substantially accurate, a track record often cited in defense of the modeling enterprise against claims that models "always run hot." His work also helped establish modern estimates of [[Climate Sensitivity]] and emphasized the role of paleoclimate evidence in bounding it. ## From Scientist to Activist Hansen grew increasingly outspoken that the science demanded action, and he clashed with political minders. During the second Bush administration he publicly accused the government of attempting to censor his communications, an episode that became emblematic of political interference in climate science. After leaving NASA in 2013 he became a full-time activist, getting arrested at protests, opposing what he viewed as inadequate cap-and-trade approaches in favor of a carbon fee-and-dividend, and warning that mainstream projections understated the risk of rapid ice-sheet collapse and [[Sea Level Rise]]. His transition from buttoned-down government scientist to civil-disobedience activist made him a complicated figure even among allies, and a frequent target for opponents who used his activism to argue, fallaciously, that his science was therefore biased. ## Connections Hansen is a central figure in the history of [[Climate Science]], a builder of [[Climate Models]], and a contemporary of [[Michael Mann]] and [[Charles David Keeling]]. For the field overview, see [[Climate Science]].