A Question for Global Warming Deniers

I have a question for global warming deniers. If you were a Martian, and you wanted to know if Earth was undergoing global warming, what kind of evidence would be sufficient for you? My guess is that the reams of data gathered by scientists all over the world on this subject would be more than sufficient to convince you. So why is it that, as an Earthling, you refuse to accept the reality of global warming? I think it has something to do with human capacity for denial, especially when it comes to worst-case scenarios that we simply find too unpleasant to contemplate. Sort of like the person who just can't admit to themseleves that their kid is doing drugs, despite overwhelming amounts of evidence from all angles (kids he hangs out with, smells coming from room, drop in academic performance, money missing from your wallet, etc. etc.). Thoughts?