I think its nothing more than a stellar and planetary cycle. although we are certainly responsible for trashing the things that help deal with the heat. I also believe pollution does facter somewhat. I've read an article written by some astronomer that said the issue is nothing more than the sun is beginning a hotter cycle and the earths orbit has become more elliptical/less elliptical. Meaning that the earth warms up. Apparently this happens every 1500 years or so. Could be true, might not. Don't know and frankly I don't want to start an arguement so please don't quote me.