Once upon a time, an oil billionaire, Charles Koch, decided to "red team" the whole climate science establishment. He hired a known climate skeptic with impeccable credentials - a physics professor at UC Berkeley named Richard Muller. Muller hired chemists and more physicists and they built their own climate model (these things run on supercomputers) from scratch, making their own assumptions about how the variables interact etc.
"Three years ago I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming," Muller wrote. "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."
https://www.scientificamerican.com/article/converted-contrarian-argues-humans-to-blame-for-climate-change/
