I just need a sentence or two to start my brain,
Ha ha, you know yourself well, and this is a good way to explain how it is for all of us. We need to kick start our brains. :-)
But if you are knowledgeable about global warming, this is easy, and if you are not, it is impossible. You cannot just sit down and write it.
Google these terms:
global warming positive feedback
global warming atmospheric concentration of greenhouse gases
climate change arguments
climate change natural
climate change human activity
Like Nancy said, it is great to use some statistics that you find in these searches.
Also, write some good body paragraphs. Do not try to write the intro until you have written a few paragraphs. :-)