Gavin Schmidt on RealClimate gives his take on Michael Crichton's new anti-global warming novel. Schmidt's discussion reads like a fundamental primer on the subject. My favorite bit:

The characters visit Punta Arenas (at the tip of South America), where (very pleasingly to my host institution) they have the GISTEMP station record posted on the wall which shows a long-term cooling trend (although slight warming since the 1970’s). "There’s your global warming" one of the good guys declares. I have to disagree. Global warming is defined by the global mean surface temperature. It does not imply that the whole globe is warming uniformly (which of course it isn’t). (But that doesn’t stop one character later on (p381) declaring that "..it’s effect is presumably the same everywhere in the world. That’s why it’s called global warming"). Had the characters visited the nearby station of Santa Barbara Aeropuerto, the poster on the wall would have shown a positive trend. Would that have been proof of global warming? No. Only by amalgamating all of the records we have (after correcting for known problems, such as discussed below) can we have an idea what the regional, hemispheric or global means are doing. That is what is meant by global warming.