The EPA is providing free climate change related content material for middle school kids.
You can get the material HERE.
In my opinion, even though this material is aimed at middle school audiences, it is all potentially useful in high school as well depending on the class you are running. For instance, if you have a climate change related module in your 10th grade biology class, some of this material will make excellent handouts.
I would like to recommend an exercise, perhaps for extra credit. FOX News went apoplectic about the idea that a federal agency full of expertise on climate and environment issues would actually provide educational material for American students. You should have the students cover some of the material provided by the EPA, discuss it in class, etc., then show them any one of several videos of Fox News getting it all wrong and have the students critique it!
For a compilation of Fox News gaffs linked directly to the EPA educational material, check out this post at Media Matters.