n the backlash against environmentalism in the era of former US president Ronald Reagan.
Things changed in 1988, a summer of record heat and droughts in the United States, when James Hansen of the Goddard Institute of Space Studies at the National Aeronautics and Space Administration (NASA) delivered his now-famous testimony to Congress.
Hansen declared he was 99 percent certain that the man-made greenhouse effect had been detected -- and that it was starting to affect the climate.
Although Hansen came under fire by fellow scientists who thought his pronouncements premature or even alarmist, the media splashed his testimony and "global warming" entered the general vocabulary.
Within months, the UN and the World Meteorological Organisation (WMO) set up a paramount scientific authority, the Intergovernmental Panel on Climate Change (IPCC), tasked with assessing greenhouse gases and their impact on the climate.
In 1992, the Rio Summit delivered the UN Framework Convention on Climate Change (UNFCCC), which in turn fathered the Kyoto Protocol on tackling greenhouse gases.
The IPCC has issued four reports since 1990, delivering judgements that are progressively more emphatic -- call it gloomy -- about the nature and severity of climate change.
They have also become profoundly influential, forcing sceptics into silence, prompting fossil-fuel companies to display green credentials and encouraging President George W. Bush to acknowledge climate change as a long-term challenge.
Weart, who is director of the Center for the History of Physics at the American Institute of Physics (AIP) in College Park, Maryland, says two other factors have been big in changing opinion in the United States.
One is former US vice president Al Gore who "has changed elite opinion" with his docu-movie "An Inconvenient Truth", said Weart.
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