SO much has been written about it that it is easy to find information and examples. You should start by googling "global warming" and "controversy" ...
Oh, I just tried that, and there is a wikipedia entry for Global Warming Controversy. So, check that out. Then type "global warming" into Google Scholar or some database with articles. You can decide if you believe in global warming or not. Form an opinion as you read. Every time you read something, write a paragraph about it. You'll have a paper in no time!
Kevin, EssayForum.com