The truth about global warming is that nobody really knows the truth, that's why people get so testy about it. When both sides can make valid arguments on an issue, I think we're all better off if they shut up about it.
Whether you believe in global warming or not, I think its reasonable to include a built-in penalty in the game for heavy pollution, more than just the pollution that shows up on the map and can be cleaned up in 1 turn.
Although a funny thing I saw on my latest game - I got the following message:
"Plains have become Tundra due to global warming."
That may not be the exact text, but somehow the planet got WARMER and my temperate climate became a FROZEN WASTELAND. huh? If turning plains and grasslands into tundra is a way to get people to clean up pollution, it would be very effective, but for God's sake, come up with a different name for it!