Climate change is a huge threat to the planet and denialism coming almost solely from the GOP is making it impossible for the US to tackle it. I agree that science denialism isn't directly a threat to the country, though the general anti-intellectualism of the Republican party has undermined our status as the world leader in generating scientific knowledge, which has an indirect but huge impact on our overall economic growth prospects.
You segue between different elements of climate change alarmism without relating it back to politics.
1) Is anthropogenic climate change real?
2) If true, how catastrophic will it be? If at all?
3) If catastrophic, how much control does humanity have over mitigating the results in a controlled and predictable fashion?
4) If we humans do have some control, how much of a role will US politics matter to these projections?
5) Finally, how far out into the future do these projections go?
You're only dealing with question #1, but many Republicans, such as myself, think that is the least relevant political question.
And so climate change denialism, to me at least, is less about believing in the issue of anthropogenic climate change itself and more about disbelieving the projections and heavy skepticism about our role in changing them to our benefit through public policy.
In talking to many Republicans, I believe that is where their skepticism is heaviest. They simply don't believe that you have any idea about the possible results or how to control them with any finesse. So they simply deny it. All of it.
California under the faux-Republican Terminator passed SB32, which was a stupid bill designed to make environmentalists in the state feel good about themselves, but it didn't do a Goddamn thing about global warming. How could it? It only affected California, which is far too marginal to the increase in global carbon to matter.
This is climate change in action. Feel-good stupidity piled on top of feel-good stupidity.