"No, I don't believe it. This is not happening".And then Willis would write a series of posts on his blog citing the "facts" researched by denialist "scientists" that "proved" the climate catastrophe was not happening. And then he'd go on living his life as if it wasn't. Meaning, of course, he would be one of the first to die.
Although, before he died he'd say "no, no... No I just, I just said that to avoid admitting the truth". No, just kidding. There is absolutely nothing that could happen that would cause Willis Hart to admit that he's wrong.
Granted, the movie is silly fiction, but that does not change the fact that global climate change is a very real threat caused by human-released CO2.
And in regards to doing something about that (reducing CO2 emissions), Willis Hart says "failure is definitely an option".