A climate scientist who was formerly dismissive of climate change now describes himself as "a converted skeptic." Richard Muller, a professor of physics at the University of California, Berkeley, and cofounder of the Berkeley Earth project, wrote in a column in The New York Times (July 28, 2012), "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."
Muller's volte-face was based on the project's analysis of "a collection of 14.4m land temperature observations from 44,455 sites across the world dating back to 1753," according to the Guardian (July 29, 2012); Muller wrote in the Times, "Our results show 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." The analysis (and related papers) from the project is not yet been published; it is presently undergoing peer review at the Journal of Geophysical Research.
Michael Mann of Penn State University told the Guardian that he welcomed the Berkeley Earth project's results as "demonstrat[ing] once again what scientists have known with some degree of certainty for nearly two decades." He added, "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. They are certain to be attacked by the professional climate change denial crowd for their findings." (A minor irony is that the project is partly funded by the Charles G. Koch Charitable Foundation, which is connected to various efforts to promote climate change denial.)