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Ex-climate change skeptic: Humans cause global warming

Global warming not only is real, but "humans are almost entirely the cause," a self-described former climate change skeptic has declared.

"Call me a converted skeptic," Richard A. Muller, University of California, Berkeley physics professor said in an opinion piece posted online Saturday in The New York Times.

Muller in October released results from the Berkeley Earth Surface Temperature (BEST) project, set up for global warming skeptics, that showed that since the mid-1950s, global average temperatures over land have risen by 0.9 degrees Celsius (1.6 degrees Fahrenheit).

In his new statement, Muller said, "Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I’m now going a step further: Humans are almost entirely the cause."

He credited his turnaround to "careful and objective analysis" by BEST, explaining:

“Our results show that the average temperature of the earth’s land has risen by two and a half degrees Fahrenheit over the past 250 years, including an increase of one and a half degrees over the most recent 50 years. Moreover, it appears likely that essentially all of this increase results from the human emission of greenhouse gases. These findings are stronger than those of the Intergovernmental Panel on Climate Change, the United Nations group that defines the scientific and diplomatic consensus on global warming. ... ”

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Money for the BEST study came from five foundations, including one established by Microsoft founder Bill Gates and another from the Charles Koch Charitable Foundation, set up by the billionaire coal magnate and widely seen as a source of money for conservative organizations and initiatives that have fought efforts to curb greenhouse-gas emissions.

Muller's website says the BEST findings will be released Monday.

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Muller said in his opinion piece he remains skeptical of some climate-change claims.

"Hurricane Katrina cannot be attributed to global warming. The number of hurricanes hitting the United States has been going down, not up; likewise for intense tornadoes. Polar bears aren’t dying from receding ice, and the Himalayan glaciers aren’t going to melt by 2035."

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