In the current issue of Nature, Quirin Schiermeier has a great rundown of some of the liveliest debates within climate science right now. No, none of them involve the question of whether humans are warming the planet—that's very well settled. But there are still some major gaps in understanding, and important areas where there's not any consensus at all.
Climate models, for instance, have plenty of blind spots in trying to predict how rising temperatures will impact small areas of the globe—the models aren't very fine-grained, which makes it hard for some countries to know exactly what to prepare for. The same goes for precipitation; everyone agrees that subtropical regions will get drier and higher latitudes will get wetter, but not a whole lot beyond that. The effects of aerosol pollution also still need a lot of study. And, yes, there are still disputes about tree-ring data. It's definitely worth reading for anyone bored by the pseudo-debate over whether global warming's a hoax or not and wants to get a better sense of the actual areas of contention.