This is a good question. In order to have a successful paper, you will need a strong thesis, a few supporting points for your thesis, and a conclusion that summarizes your main points. So, if you are writing on global warming, then you want a thesis that supports the theory of global warming or refutes it. For the rest of this answer, I will assume that you are writing to defend the idea of global warming.
What you will need now are supporting points. So, ask yourself, why you believe in global warming. You might want to use the evidence that scientists have published, temperature increases in the summer months, or something else that might support your thesis. You might also look at legislation from a global point of view, like the Kyoto protocol. In other words, the bulk of your research comes here. I will add a few link that will give you information.
Finally, you want to conclude your essay with a summary of your thesis and main point. In other words, show your reader why your thesis was a compelling one.
I would, if you haven't already, research Chlorofluorocarbons and Atmosphere or Ozone depletion, and although his information isn't quite accurate, Al Gore.
Hope that helps!