it doesn't mean that humanity polluting the air is not a massive problem.
correct, the general point is arguing climate change is just dumb because it was global warming, many predictions were/are wrong etc.
Now, imagine if you told someone the pollution particles are x ppm and when it reaches x+y it can trigger asthma or cause lung damage etc and here are the studies for cities in Kommyfornia. Pretty hard to argue against that imo. Same can be done with water. Are you familiar with the Love Canal? This sort of pollution is nothing new, though most of the incidents haven't been nationwide but those are documented, explainable and could be extrapolated.
Even Trump says we need the cleanest air and water we can get. I'm not sure his actions have addressed that yet but he's certainly said it a few times.