Welk....take, for instance, the kyoto protocol. This was the major solution proposed to address climate change a while ago. I believe the UN estimated it would take 150B/yr to implement, and it would delay the damage we would experience in 2100 by 6 years. Not a lot of benefit for the $150B/yr. Compare that to their estimation (the UN's estimation) that we could completely address sanitation, clean drinking water, basic healthcare, and basic education to every human on the planet for $75B.
From the UN data -- 2 billion people are infected by malaria every year. We could spend $13B/yr (again, UN estimate) to bring that down by 50%. This would save 500M lives every year. Right now, not 100 years from now.
We could apparently avoid 28 million new cases of HIV/AIDS for $27B/yr. Mostly in 3rd world countries. Now.
Global warming is a problem, but it's way down the list. I mean, there is probably a non-trival chance an asteroid could hit earth and wipe us out. We ought to do something about that -- Given the magnitude of that problem, I'd say we should devote a little to it. I think there's a good argument to be made that asteroid extinction should rank higher than climate change.