"John H. Sununu might count. He was an MIT educated engineer, brilliant guy, PhD in mechanical engineering. He even served on MIT's Advisory Board of the Technology and Policy. He remains a member of the National Academy of Engineering. More importantly, he was a governor of NH and later the White House Chief of Staff under George H.W. Bush.

As Bush's adviser, he was the first one with a STEM background to doubt climate change. He publicly questioned the validity of James Hansen / NASA's modeling efforts. In fact, the US was on the verge of signing a binding climate treaty with 65 other nations (in 1989!)

Prior to this point, the argument was "how do we balance emission reductions versus economic losses", with conservative forces recognizing the danger but insisting we protect businesses from overreaching regulation. After Sununu's public doubts, the entire debate shifted to "is climate change even real?". It inspired the "everything's fine" PR campaign that has been ongoing ever since. I honestly suspect treaty opponents didn't even realize that pure denial would be a realistic strategy until Sununu called James Hansen a liar.

I guess in another 50 years we'll see the true extent of the damage he did. Ironically all this falls not on some moron, but on a brilliant guy who decided to speak on something outside his expertise."