James E. Hansen, the climate scientist who issued the clearest warning of the 20th century about the dangers of global warming, will retire from NASA this week, giving himself more freedom to pursue political and legal efforts to limit greenhouse gases.<\/p>\n
His departure, after a 46-year career at the space agency\u2019s Goddard Institute for Space Studies in Manhattan, will deprive federally sponsored climate research of its best-known public figure.<\/p>\n
At the same time, retirement will allow Dr. Hansen to press his cause in court. He plans to take a more active role in lawsuits challenging the federal and state governments over their failure to limit emissions, for instance, as well as in fighting the development in Canada of a particularly dirty form of oil extracted from tar sands.<\/p>\n
\u201cAs a government employee, you can\u2019t testify against the government,\u201d he said in an interview.<\/p>\n
Dr. Hansen had already become an activist in recent years, taking vacation time from NASA to appear at climate protests and allowing himself to be arrested or cited a half-dozen times.<\/p>\n
But those activities, going well beyond the usual role of government scientists, had raised eyebrows at NASA headquarters in Washington. \u201cIt was becoming clear that there were people in NASA who would be much happier if the \u2018sideshow\u2019 would exit,\u201d Dr. Hansen said in an e-mail.<\/p>\n
At 72, he said, he feels a moral obligation to step up his activism in his remaining years.<\/p>\n
\u201cIf we burn even a substantial fraction of the fossil fuels, we guarantee there\u2019s going to be unstoppable changes\u201d in the climate of the earth, he said. \u201cWe\u2019re going to leave a situation for young people and future generations that they may have no way to deal with.\u201d<\/p>\n
His departure, on Wednesday, will end a career of nearly half a century working not just for a single agency but also in a single building, on the edge of the Columbia University campus.<\/p>\n
From that perch, seven floors above the diner made famous by \u201cSeinfeld,\u201d Dr. Hansen battled the White House, testified dozens of times in Congress, commanded some of the world\u2019s most powerful computers and pleaded with ordinary citizens to grasp the basics of a complex science. <\/p>\n