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, Berkely, 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 2½ degrees Fahrenheit over the past 250 years, including an increase of 1½ 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. "In this support, we strive to benefit society by promoting discovery and informing public policy."
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.
On his Facebook page, Mann wrote: "There is a certain ironic satisfaction in seeing a study funded by the Koch Brothers -- the greatest funders of climate change denial and disinformation on the planet -- demonstrate what scientists have known with some degree of confidence for nearly two decades: that the globe is indeed warming, and that this warming can only be explained by human-caused increases in greenhouse gas concentrations. I applaud Muller and his colleagues for acting as any good scientists would, following where their analyses led them, without regard for the possible political repercussions."
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. His latest claims provide no new insight into the climate science debate," Morano said in an email.
Muller's New York Times commentary follows research he did last year that confirmed the work of scientists who found that the 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 2½ 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."
Muller asserted that his findings were "stronger" than those of the UN's intergovernmental panel. But neither Berkeley's research from last year nor the new findings on causality have been published in peer-reviewed journals, which has raised criticism and concerns among climatologists and contrarians alike.
Benjamin D. Santer, a climate researcher at the Lawrence Livermore National Laboratory and a lead author of the 1995 UN climate report, said he welcomed the involvement of another research group into "detection and attribution" of climate change and its causes. But he said he found it troubling that Muller claimed such definitive results without his work undergoing peer-review.
"If you go into the public arena and claim to have generated evidence that is stronger than the IPCC, where is the detailed, scientific evidence? Has he used fundamental new data sets?" Santer said. "Publish the science and report on it after it's done."
He added: "I think you can do great harm to the broader debate. Imagine this scenario: that he makes these great claims and the papers arent published? This [op-ed] is in the spirit of publicity, not the spirit of science."
Elizabeth Muller, co-founder and executive director of the Berkeley project and Richard Muller's daughter, said the papers had been peer-reviewed, but not yet published. But because of the long lead-up to publication, she said, the Berkeley team decided to place its papers online, in part to solicit comment from other scientists. The papers were posted on the BerkeleyEarth.org website on Sunday.
"I believe the findings in our papers are too important to wait for the year or longer that it could take to complete the journal review process," Elizabeth Muller wrote in an email. "We believe in traditional peer review; we welcome feedback [from] the public and any scientists who are interested in taking the time to make thoughtful comments. Our papers have received scrutiny by dozens of top scientists, not just the two or three that typically are called upon by journalists."