A climate change primer
How do we get up to speed, if we need help? RealClimate posted Start here, which has information for those just getting started at understanding the issue and information for those who want more in-depth specifics.
For a slightly different take on the matter, see Gristmill's How to Talk to a Climate Skeptic (perhaps you're the skeptic you'll be talking with :-). Thanks to Brad DeLong's Grasping Reality with Both Hands for that pointer.