A United Nations report released Friday that blames humans for the "runaway train" of global warming has abruptly shifted the international debate from "Are humans to blame?" to "What are we going to do about it?"
"The world's scientists have spoken," said Timothy E. Wirth, president of the United Nations Foundation. "It is time now to hear from the world's policymakers. The so-called and long-overstated 'debate' about global warming is now over."
The 21-page report, released in Paris by the Intergovernmental Panel on Climate Change, proposed no solutions. There is no world consensus on how best to bring about the radical restrictions in emissions that would be needed to mitigate global warming.
The most significant effort to reach a common solution was the 1997 Kyoto Protocol, which so far has not had much impact.
The report said that it was "unequivocal" that global warming was occurring and that it was at least 90% certain humans were responsible. It predicted temperatures would rise 3.2 to 7.2 degrees Fahrenheit by 2100 and that sea level would rise 7 to 23 inches, perhaps more.
If the Greenland ice sheet were to melt completely, it would lead to a 21-foot increase in sea level, forcing the relocation of more than 300 million people living in low-lying areas worldwide.
The report also said warming would continue even in the extremely unlikely event that global carbon dioxide could be stabilized at its current level. Such a stabilization would require an immediate 70% to 80% reduction in emissions, said Richard Somerville of the Scripps Institution of Oceanography in La Jolla.
Although most of the scientific data behind the report have come out before, their aggregation into a single report, phrased in the boldest of terms, sparked an intense reaction Friday.
"The degree of certainty, which was already very high, is now as close to certain as scientists are willing to say," said former Vice President Al Gore, a longtime champion of environmental issues whose documentary on global warming, "An Inconvenient Truth," is nominated for two Oscars.
Echoing a phrase that was widely heard Friday, Rep. Edward J. Markey (D-Mass.) called the report "a scientific smoking gun."
The warming would have a powerful impact on California and the Southwest, with hotter weather, less rainfall and a loss of water supply because of the diminishing snowpack in the Rocky Mountains.
Deflecting criticism
