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 at 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.
In an opinion piece in Saturday's New York Times titled "The Conversion of a Climate-Change Skeptic," Muller wrote:
"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 said, "that the average temperature of the earth's land has risen by 2½ degrees Fahrenheit over the past 250 years, including an increase of 1 ½ 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 called his current stance "a total turnaround."
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 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.