I think I heard the statement but didn’t realize he was blaming the zombie apocalypse on global warming.
He wasn’t. He was saying the model for how long it would take for his cure to disperse would have to be updated because of the lack of cars, planes, factories, etc. polluting. He was just slathering on some more BS to make himself sound more plausible. It could be taken as a jab at the junk science that so many just reflexively believe, though I know the creators are liberal and probably wouldn’t go there. At least, not on purpose.