On scientific issues of direct relevance to public policy, one would hope a leading contender for the office of president would demonstrate a solid foundation of knowledge based on evidence and the current state of expert understanding.

Unfortunately, during a face-to-face interview with The Washington Post’s editorial board, Donald Trump expressed views about climate change totally out of step with the science.

At the very end of his 63-minute interview Monday, editorial page editor Fred Hiatt asked Trump: “You think climate change is a real thing? Is there human-caused climate change?”

Trump’s response:

I think there’s a change in weather. I am not a great believer in man-made climate change. I’m not a great believer. There is certainly a change in weather that goes — if you look, they had global cooling in the 1920s and now they have global warming, although now they don’t know if they have global warming. They call it all sorts of different things; now they’re using “extreme weather” I guess more than any other phrase. I am not — I know it hurts me with this room, and I know it’s probably a killer with this room — but I am not a believer. Perhaps there’s a minor effect, but I’m not a big believer in man-made climate change.

Trump begins and ends his statement referring to his lack of belief in man-made climate change. Man-made climate change is not about belief, it’s about evidence. And the evidence is overwhelming that it is happening.

Every single major scientific institution in the United States, including the National Academy of Sciences, the American Academy for the Advancement of Science, the American Meteorological Society, the American Geophysical Union and the American Institute of Physics, have published reports and/or statements affirming man’s role in climate change based on multiple lines of evidence.

The fact that the presumptive Republican nominee for president chooses not to “believe” them is very troubling. It suggests he has chosen to ignore the evidence and/or reject the conclusions of leading experts. Does Trump, a non-scientist,  somehow “believe” he knows more about climate change than the legions of scientists who have spent decades researching the issue?

Trump’s actual statements reveal he knows disturbingly little about climate and weather. He refers to global cooling in the 1920s when the temperature measurements show the climate was slowly warming. (It’s possible he meant to say the 1970s, when it slightly cooled; but this mistake reveals how little he actually knows about climate and his lack of attention to detail.)

He says scientists “now don’t know if they have global warming” when there is absolutely zero doubt, even among scientists who are unconvinced climate change poses a major threat, that the planet is warming up. The latest two years were the warmest two years on record, and the warmth in the months of January and February deviated more from average than ever before (in historical records).

And scientists do not chiefly refer to climate change as “extreme weather,” as Trump claims, they refer to the issue as climate change, as they always have. Climate change manifests itself in many ways and so climate scientists, over time, have explored different terminology for explaining its effects in different situations/contexts. It so happens climate change is known to modify extreme weather, as a report from the National Academy of Sciences released last week makes clear.

As a follow-up question, Post editorial writer Steve Stromberg asked Trump: “Don’t good businessmen hedge against risks, not ignore them?”

His response:

Well I just think we have much bigger risks. I mean I think we have militarily tremendous risks. I think we’re in tremendous peril. I think our biggest form of climate change we should worry about is nuclear weapons. The biggest risk to the world, to me — I know President Obama thought it was climate change — to me the biggest risk is nuclear weapons. That’s — that is climate change. That is a disaster, and we don’t even know where the nuclear weapons are right now. We don’t know who has them. We don’t know who’s trying to get them. The biggest risk for this world and this country is nuclear weapons, the power of nuclear weapons.

The problem with this response is that man-made climate change is real and happening now.  The detonation of a nuclear bomb is a hypothetical.

Although a nuclear explosion would have more immediate impact than climate change, whose damages accumulate over time, it is troubling that Trump neglects to concede that climate change merits any attention at all, when scientists have been so vocal about the dangers it poses.

Can’t/shouldn’t a candidate for president of the United States devote attention to multiple kinds of risks? Or at least expend the effort to understand them and give them consideration?