The 2012 date has absolutely nothing to do with global warming. It was predicted by the ancient Maya more than 1000 years ago, long before we started burning coal and oil.
Tell me, where did you learn that 2012 and global warming are connected? Did someone tell you that, or did you just assume?
The Date 12/21/12 is not when global warming will cause the end of the world as we know it. Of course what others say about global warming making the world end isn't true either.
No you can't. You are just a gnat on the back of flea in the bigger picture. With heroic efforts of your kind, you might decrease temperature 1/4 of a degree. If you live in AK, it will be minus 24 degrees in stead of minus 24.25. if that makes you feel better, then by all means fret over the difference.