IPCC - too conservative
There are certain aspects of climate science and various indicators that are still under question. However, one should not read into this as there being a debate on the matter of climate change, but rather that there are indications that the situation could be much worse than presented.
The article, "But here's what they didn't tell us. If the official verdicts on climate change seems bad enough, the real story looks far worse," tells of science regarding the ice sheets of Greenland and Antarctica. If they are really as close to disintegration as some think, the sea level rise would actually be measured in meters rather than the predicted 3.1 centemeters. Other points of worry to some scientists that won't conclusively make it into the report: the slowing gulf stream, and "carbon cycle feedbacks" or the relase of methane and other GHG as a result of permafrost melt.
The sidebar on the same page as that article, "Reasons to be cautious" discusses the debate over the terminology of "extremely likely," "likely," and "very likely" in regards to human activity causing the problem. After a 10 hour debate, and reluctance from Chinese and Saudi Arabian scientists, "very likely" was reached as meaning at least 90 percent, whereas just "likely" means greater than 66 percent, and "extremely" well over 95 percent.
While relatively short, these articles offer a fresh perspective (although saturated with a little gloom and doom) that isn't widely published in the reports about the report.