WASHINGTON -- The verdict is in: Global warming is real and greenhouse-gas emissions from human activity are the main cause. This, according to Richard Muller, professor of physics at the University of California, Berkeley, a MacArthur fellow and co-founder of the Berkeley Earth Surface Temperature project.
The U.N. Intergovernmental Panel on Climate Change and hundreds of other climatologists around the world came to such conclusions years ago, but the difference now is the source: Muller is a long-standing, colorful critic of prevailing climate science, and the Berkeley project was heavily funded by the Charles Koch Charitable Foundation, which, along with its libertarian petrochemical billionaire founder Charles Koch, has a considerable history of backing groups that deny climate change.
In an opinion piece in Saturday's New York Times, titled "The Conversion of a Climate-Change Skeptic," Muller writes: "Three years ago I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming. 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."
The Berkeley project's research has shown, Muller says, "that the average temperature of the Earth's land has risen by 2 degrees Fahrenheit over the past 250 years, including an increase of 1 degree over the most recent 50 years. Moreover, it appears likely that essentially all of this increase results from the human emission of greenhouse gases."
He calls his current stance "a total turnaround."
Tonya Mullins, a spokeswoman for the Koch Foundation, said the support her foundation provided, along with others, has no bearing on results of the research.
"Our grants are designed to promote independent research; as such, recipients hold full control over their findings," Mullins said in an e-mail. "In this support, we strive to benefit society by promoting discovery and informing public policy."
Leading climate scientists said Muller's comments show the science is so strong that even those inclined to reject it cannot once they examine it carefully. Michael Mann, director of the Earth System Science Center at Penn State, said Muller's conversion might help shape the thinking of the "reasonable middle" of the population "who are genuinely confused and have been honestly taken in" by attacks on climate science.
Muller's conclusions, however, did not sway the most ardent climate contrarians, like Marc Morano, a former producer for Rush Limbaugh and former communications director for the Republicans on the Senate Environment and Public Works Committee.
"Muller will be remembered as a befuddled professor who has yet to figure out how to separate climate science from his media antics," he said in an e-mail.