have decided that I am opposed to it.
Well, it's not so much a matter of for or against. It's about whether or not you believe it is happening and that humans are causing it.
Based on what you wrote here, it seems like you need to read some articles and write a paragraph about the main idea expressed by each author. If you study 5 articles like that, and if you can tell me the main idea expressed by each author, I think you will be ready to write.
But your ideas cannot come from this thread. They have to come from articles, and you'll cite the articles. So, search your school library's database for: global warming arguments
Try to find articles written in the past 5 years. This is like a scavenger hunt, and then you have to search through the articles' introductions to find the main idea of each. Easy, easy!!