The news is surprising given that Muller has been an outspoken, high-profile critic of climate science and his Berkeley Earth Surface Temperature project is heavily funded by the climate-denying billionaires, the Koch brothers.
Muller says that his new opinion stems from his own Koch-funded project, whose meticulous work, he said, led to the only explanation for rising temperatures was human activity.
The project's work had already made Muller confirm the existence of climate change but his new stance puts humans at the forefront.
In an Op-Ed in the New York Times, Muller was blunt about his reversal.
“Three years ago I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming, he wrote in an Op-Ed column for the New York Times.
"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 Los Angeles Times said that Muller calls his stance a total turnaround.
The newspaper also reported comments from leading climate expert Michael Mann of Penn State on his Facebook page after the news.
“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."
The Christian Science Monitor pointed out that the words only confirm what most scientists have already agreed upon: that human-made global warming was real.
Indeed the project's results were found to make similar conclusions to famous prior studies like NASA's Goddard Institute for Space Studies in New York, the Hadley Center for Climate Prediction and Research in Britain, and the National Oceanic and Atmospheric Administration (NOAA).