NASA veteran a key player in global warming debate

James Hansen, a 37-year NASA veteran who directs the agency's Goddard Institute for Space Studies, is the kind of expert whom presidents turn to for scientific briefings on climate change. Shortly after George W. Bush moved into the White House, for instance, he invited Hansen to talk to top administration officials about the issue.

On one of those visits, Hansen took part in a polite debate with Massachusetts Institute of Technology scientist Richard Lindzen, who questions the scientific underpinnings of climate change. Hansen is convinced that global warming is real and that the consequences are potentially disastrous.

"Among well-qualified scientists who have analyzed the data in detail, there is now a reasonable consensus that humans are a primary cause of the warming," he said, while warning that the Earth's "atmospheric composition is changing before our eyes."

Hansen is best-known on the Washington political scene for sounding the alarm about global warming during the 1980s, when he and his NASA colleagues gave high-profile testimony before Congress. Those presentations helped build political and scientific momentum for U.S. approval of the 1992 United Nations framework convention on climate change. Under that agreement, President George H.W. Bush pledged to stabilize U.S. greenhouse-gas emissions, although the accord included no deadlines.

Since then, many other pre-eminent scientists have expanded the scientific understanding of global warming. But Hansen's research continues to carry significant weight in scientific circles.

Last December, he co-authored a study boosting the argument that black carbon -- or soot from cars, coal-fired power plants, and wildfires -- may be affecting the way the sun reflects off snow and thus accounting for a quarter of all global warming. Hansen's March 2004 article in Scientific American warned that carbon dioxide emissions and soot are speeding up global warming, which, he wrote, "is having noticeable impacts as glaciers are retreating worldwide, Arctic sea ice has thinned, and spring comes about one week earlier than when I grew up in the 1950s."

Hansen, 63, spent his formative years in Denison, Iowa, which, he proudly relates, was the hometown of the late actress Donna Reed. He received his undergraduate degree from the University of Iowa and did his graduate studies at the Universities of Kyoto and Tokyo and at Leiden University in the Netherlands.