Steven Koonin was an assistant professor of physics at Caltech, now an engineering professor at NYU, and was chief scientist at BP from 2004-2009 and Under Secretary of Science at the Department of Energy under Obama.

He's been travelling the country advocating against decarbonization. He wrote a book "Unsettled" (which I have not read) where he makes various arguments against decarbonization.

He made this 43-minute video:

In the video, he makes the following claims:

• Climate models are so inaccurate they're useless. So he ignores them and predicts that we will have as much warming between now and 2100 as we've had in the last 100 years, which seems to be a prediction based on gut instinct alone.
• He claims that the impacts on humans of warming between now and 2100 will be no greater than the impacts of global warming over the last 100 years. This is very dubious -- sea level with not rise linearly with more warming -- sea level rise will accelerate as the planet warms more, and there are large land-based ice sheets in Greenland and Antarctica which are hard to model and predict which may break loose suddenly and catastrophically, causing a lot of sudden sea level rise. And sea level rises a lot locally during storms, like when it rose several feet during hurricane Sandy, flooding the R and L subway tunnels between Manhattan and Brooklyn. So as sea level rises, the amount of flooding during storms increases. Also, the polar regions have warmed up a lot more than 1.3 dgrees C already, global wind patterns are driven by the gradient of temperature as latitude increases, so with another 1.3 degrees C of warming, global wind patterns will change radically.
• He says most commentary on climate change in the mainstream media is wildly inaccurate. He's right about that.
• He never discusses nuclear energy in the video. I saw him give a lecture at a local Republican club, and asked him about using nuclear to solve climate change. He said he likes nuclear, but did not come up with any reason why pursuing it aggressiely wasn't a good idea, and the moderator wouldn't let me ask any more questions.
• He argues that rapid decarbonization to net zero by 2050 would cost 5-7% of GDP every year. I don't know what estimates anyone else makes on this cost, but it will be cheaper if we decarbonize at a lower rate, or if a next-gen nuclear technology turns out to be cheaper than fossil fuels, but Koonin seems to against making any effort at all over any time frame.

Koonin's argument that we should ignore the climate modeling predictions of warming and impacts based on tremendous effort by experts and computer models while trusting his guesswork based on gut instinct alone is an awful stretch. He is arguing that we should pretty much forget about global warming, not worry about it, and emit as much greenhouse gases as we want. To make that argument, he has to argue that we somehow know with high confidence that no great harm will come of that, and it's going to take more than gut instinct to make that argument with any credibility.

One has to keep in mind that he has no lack of speaking engagements. Conservatives love hearing what he has to say.