> if a person believes that yes, it's likely that humans are having some effect on climate, but that we aren't sure exactly what it is and how harmful it will be over a period of time - are they a "denier"?

Yes 100% they are a denier. This was a position that was valid in the 80s. It's also exactly the bs talking point spread by those who profit from us not moving away from fossil fuels. Confuse and delay as much as possible and discredit those pesky scientists with their models that can't decide if it'll be terrible or catastrophic.