By Juliet Eilperin
An international panel of climate scientists said yesterday that there is an overwhelming probability that human activities are warming the planet at a dangerous rate, with consequences that could soon take decades or centuries to reverse.
The Intergovernmental Panel on Climate Change, made up of hundreds of scientists from 113 countries, said that based on new research over the last six years, it is 90 percent certain that human-generated greenhouse gases account for most of the global rise in temperatures over the past half-century.
Declaring that "warming of the climate system is unequivocal," the authors said in their "Summary for Policymakers" that even in the best-case scenario, temperatures are on track to cross a threshold to an unsustainable level. A rise of more than 3.6 degrees Fahrenheit above pre-industrial levels would cause global effects -- such as massive species extinctions and melting of ice sheets -- that could be irreversible within a human lifetime. Under the most conservative IPCC scenario, the increase will be 4.5 degrees by 2100.
Richard Somerville, a distinguished professor at the Scripps Institution of Oceanography and one of the lead authors, said the world would have to undertake "a really massive reduction in emissions," on the scale of 70 to 80 percent, to avert severe global warming.
The scientists wrote that it is "very likely" that hot days, heat waves and heavy precipitation will become more frequent in the years to come, and "likely" that future tropical hurricanes and typhoons will become more intense. Arctic sea ice will disappear "almost entirely" by the end of the century, they said, and snow cover will contract worldwide.
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