I have always thought that a thesis statement should be like the beginning of a sales presentation. It should be designed to sell an idea to the reader. The ultimate objective of the entire essay should be to get the reader to figuratively sign on the dotted line, and the body of the essay should be designed to convince the reader to sign. The thesis statement has to tell the reader what you are going to try to sell him, but it shouldn't be too forceful because your reader may be a tough customer and need a lot of persuasion. If, for example, you are trying to get people to vote for Barack Obama, you should remember that your reader might be a die-hard Republican. A good thesis statement should catch the reader's attention, which means it should be original. You should keep in mind what it is that you want your reader to do. If climate change is endangering the entire world, your thesis should say or imply that your reader is causing some of the problem and that he can help solve the problem. It seems to me that you can either (1) try to prove that the climate is really changing drastically, or (2) take it for granted that the climate change is real and discuss what can be done to cope with the problem. But I don't think you should try to do both. And your thesis statement should say what aspect of the situation you intend to discuss. Students are always asking for advice about thesis statements. I believe that they should do some research on their topic first and even write some of the body of the paper before they write their thesis statement. They ought to find many good examples of thesis statements in their reading and can use one of them with a little modification. Get your reader to sign on the bottom line.