This just in: trying to stop climate change will cost the world about $50 trillion a year, but the impacts of climate change will only cost about $1 trillion a year, so the choice is clear! That's the thesis of Bjorn Lomborg's op-ed in Monday's Washington Post.
Presumably the flooding of much of Bangladesh doesn't count for much, since those lives are totally worth less than ours, etc.
Update: For more on this, see Joe Romm and Miles Grant.