A bunch of BULL PUCKY.
I love how "global warming" has brought about cooler summers here in Texas for about the last five years.
If that's global warming, bring it on!
To answer your question, I believe the temperature of the earth rises and falls naturally. There is no science to prove that mankind has caused any of this. Kind of like there's no science to prove that embryonic stem cell research will result in the cure for paralysis, cancer, diabetes, etc. Makes for a good story, though.