By David Perlman

The hot issue of global warming got hotter Monday when a UC Berkeley physicist, once a loud skeptic of human-caused climate change, agreed not only that the Earth is heating up, but also that people are the cause of it all.

Richard Muller converted only a year ago to the idea that the world has been warming for decades. Before then he had argued that global warming data — even figures compiled by United Nations experts — were badly flawed.

Now Muller is going further, blaming the warming almost entirely on human emission of greenhouse gases, most notably carbon dioxide — a conclusion that almost all climate scientists reached long ago.

Muller argued that the evidence from more than 36,000 temperature stations worldwide shows that the global thermometer has risen by 2.7 degrees Fahrenheit over the past 250 years. The warm-up began with the onset of the Industrial Revolution, Muller said, and has accelerated in recent years.

Fierce debate

Muller released five scientific papers Monday supporting conclusions reached by his organization Berkeley Earth with detailed evidence. They immediately set the blogosphere afire, with experts and not-so experts jousting over the conclusions.

Scientists who entered the fray criticized Muller on two fronts:

* Of the five papers, only one has been submitted to a peer-reviewed scientific journal, and that one hasn’t been published yet.

* His organization has been heavily financed by the Charles Koch Foundation, best known for supporting the most prominent “deniers” of global warming as well as conservative political organizations. That indictment came from climate scientists when Muller was among the deniers, but some bloggers remain suspicious of him even now.

Koch and his brother, David Koch, made their fortune in the oil refining and chemical business. Charles Koch’s foundation has given Muller a $150,000 grant to conduct his research, the Berkeley physicist said.

“All he wants is the science, and we have unfettered use of his money,” Muller said.

Started in 1700s

Muller said detailed analysis by Robert Rhode, a physicist and statistical analyst on his team, shows that global land surface temperatures have been rising along with emissions of carbon dioxide ever since the mid-18th century.

“That carbon dioxide evidence just hit me like a brick wall,” Muller said. “To me it was a shocker.”

The greenhouse gas evidence, he said, came from analyzing air samples trapped in ice cores from Greenland and Antarctica, where the cores hold air bubbles and particles going back tens of thousands of years.

His group’s records show that “global cooling periods” during the century before 1850 were caused by ash clouds from three tremendous volcanic eruptions — but that even by then, global warming had begun.

Invitation to critics

Muller said he has released most of his group’s findings without going through peer review so scientific opponents could air their criticisms without waiting a year or more for the papers to be published.

Climate scientist Richard Lindzen of Harvard, one of the most influential critics of global warming adherents, promptly took Muller up on the offer.

“There has never been much argument that the global mean temperature anomaly has increased a small amount since the Little Ice Age,” Lindzen said in an e-mail, referring to a global period of colder weather that some theorists say may have ended roughly 450 years ago. “There is no reason to believe that Muller’s estimate is any better than anyone else’s.”

And asked about Muller’s carbon dioxide evidence, Lindzen said, “Muller’s argument is naive and even silly. Given the triviality of his results and their lack of importance, it is hard to understand what he is doing.”

Source of conversion

Muller is a professor of physics at UC Berkeley and a senior scientist at the Lawrence Berkeley National Laboratory. He is the popular author of “Physics for Future Presidents,” and his newest book is called “Energy for Future Presidents.”

Asked what prompted him to change his mind on global warming, Muller said Rhode’s analyses of temperature data covering hundreds of years and from thousands of newfound climate stations — including records by Thomas Jefferson and Benjamin Franklin — were too powerful to ignore.

“I didn’t expect to get such clear data,” Muller said. “It has cleared up a lot of Augean stables, and I hope it opens up the discussion rationally.”

Read up: The scientific papers and data from UC Berkeley physicist Richard Muller and his group can be read at Berkeleyearth.org.

— Reach David Perlman at [email protected]

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