Climate Change Warning: Hansen Testifies Before Senate

NASA’s top climate scientist looked a Senate committee in the eye and said what no government official had been willing to say publicly. On June 23, 1988, James Hansen testified before the Senate Energy and Natural Resources Committee that he was "99 percent confident" that global warming was caused by the buildup of carbon dioxide and other greenhouse gases in the atmosphere, not natural climate variation. The hearing room was deliberately hot: Senator Tim Wirth had opened the windows the night before and turned off the air conditioning. Hansen was no fringe figure. As director of NASA’s Goddard Institute for Space Studies, he had spent years building computer models of the Earth’s climate system. His testimony drew on decades of temperature data showing the planet warming at a rate consistent with rising CO2 levels from fossil fuel combustion. He told senators the warming trend was already detectable above normal climate noise and would intensify substantially in coming decades, producing more extreme heat waves, droughts, and storms. The testimony landed on the front page of the New York Times and catapulted climate change from a technical debate among atmospheric scientists into a mainstream political issue. Within months, the United Nations established the Intergovernmental Panel on Climate Change, and international negotiations that would eventually produce the Kyoto Protocol began taking shape. Hansen became the public face of climate science, a role that would bring him into increasing conflict with political appointees who tried to edit his public statements. Nearly four decades later, Hansen’s 1988 projections have proven remarkably accurate. Global temperatures have tracked closely with his middle-range scenario, and the extreme weather events he warned about have arrived with the frequency his models predicted. His testimony remains the single most consequential moment in the public history of climate science.