This is an iBook. It can be downloaded for free from the iBook Store and read on any device that can run the iBooks app.
It will be suitable for middle to senior classes, or anyone who wants to understand the problem from a basic background of scientific understanding.
It covers the origins of the problem, consequences and solutions.
Click on the cover to go to the iBooks Store.
If you don't have access to a gadget, use this link to get a PDF version. Certain features (embedded movies; live glossary) won't work.