An iBook
This text can be downloaded free from the iBooks store, and read on any device that can run the iBooks app.
The text has some interactive features ... a couple of short videos and a live glossary, that help explain some of the more complicated or unfamiliar ideas in the science of the climate problem.
It should be perfectly accessible to senior school students and anyone else who wants to discover more about the problem - how we came to have it, and what we need to do.
A pdf version, without the interactive stuff, can be read or downloaded using this link.