Wally Broecker, a pioneer in the science of rapid ciimate change, has made several of his climate science books available as free PDFs.

The Business Executive's Guide to Global Warming is an excellent summary, while The Role of the Ocean in Climate, Fossil Fuel CO2 and the Angry Climate Beast, and (cute title award) The Glacial World According to Wally will reward closer reading.

The books are hosted on the site of the Gary Comer Abrupt Climate Change Fellowships, established by the billionaire founder of the mail-order retailer Land's End. According to this BBC story on the warming of Greenland, Gary Comer "has devoted his retirement to the science of global warming".