Muller is not a climate-change denier. He concedes that the world is warming and that human enterprise is playing a role. He insists, however, that it’s unclear just how much temperature trends correlate with greenhouse-gas emissions. And when hacked e‑mails from climate scientists caused global-warming skeptics to cry foul and accuse the experts of manipulating data, Muller chimed in to suggest that his comrades in science might not be so trustworthy. The skeptics, he said, had legitimate concerns. He saw risks of bias everywhere in the existing climate research.

And so, in 2010, he gathered a team of physicists and statisticians—the Berkeley Earth Surface Temperature project (BEST)—and set out to evaluate findings on global temperature trends from NASA,NOAA, and a research group in the U.K. He would use the same data those agencies did. Muller’s project is funded in part by the foundation of one of the oil-billionaire Koch brothers, and his invitation to testify this spring before the House Committee on Science, Space, and Technology was orchestrated by Republicans. To plenty of spectators, that was really all we needed to know. The conservative Koch brothers have a right to the scientific answers they pay for.

Then came Muller’s testimony. Confounding expectations, he reported “a global warming trend that is very similar to that previously reported by the other groups.” In his testimony, he cited data indicating that the Earth had warmed 0.7 degree Celsius since 1957, with man-caused warming contributing 0.6 degree C. He summarized: “I believe that some of the most worrisome biases are less of a problem than I had previously thought.”

Illustration: Anje Jager