Yes, they will hear them. But if they then google what the deniers say, and it is complete bullshit, then their conclusion will likely be "hmm, another Internet idiot." If they google what the deniers say, and find the 1970 claims of ice age Armageddon, and Billy's claims that "about half of humanity [might] die in less than a month" they will think "hmm, they're right; those supposed 'climate scientists' do say some stupid things." Most people are pretty good at detecting bullshit. But clearly stating facts, rather than supposition, is most certainly not in vain. Indeed, it is the ideal that we expect deniers to hew to, and the ideal that we should hold ourselves to as well. Sure, they can be considered. We also might have a massive volcanic eruption that plunges us into 20 years of global cooling - and only our excess of CO2 will save us. That can also be considered, although that scenario is also very, very unlikely. Now imagine what you would say to a denier who claims "if a volcano erupts, only CO2 will save us from extinction!" I suspect you might take issue with his remarks.