Climate change skeptic reverses course

WASHINGTON – The verdict is in: Global warming is real and greenhouse-gas emissions from human activity are the main cause.

This, according to Richard A. Muller, professor of physics at the University of California, Berkeley, a MacArthur fellow and co-founder of the Berkeley Earth Surface Temperature project.

The United Nations 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 G. 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 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.”

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 email.

Some leading climate scientists said Muller’s comments show that the science is so strong that even those inclined to reject it cannot once they examine it carefully.

Michael E. Mann, director of the Earth System Science Center at Pennsylvania State University, 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 New York Times commentary follows research he did last year that confirmed the work of scientists who found that Earth’s temperature was rising. In the past, Muller had criticized which global temperatures had been used in such research, contending that some monitoring stations provided inaccurate data. Now, Berkeley’s research has weighed in on the causes of the temperature rise, testing arguments that climate contrarians have used.

“What has caused the gradual but systematic rise of two and a half degrees?”Muller writes. “We tried fitting the shape to simple math functions (exponentials, polynomials), to solar activity and even to rising functions like world population. By far the best match was to the record of atmospheric carbon dioxide, measured from atmospheric samples and air trapped in polar ice.”