The word, in the context you’re using it, is obviously a callback to “holocaust denier”. But the Holocaust is an established historical fact… not a theory, however sound.

You can call people “global warming deniers” when you’re standing on a 50% smaller United States in 2075… but it’s pretty much the height of hubris to use the term now, and I think you might want to re-evaluate it; it puts a major dent in your credibility. At least to me.