For those not familiar with it, the Intergovernmental Panel on Climate Change was set up in 1988 to write periodic assessments of the state of climate science. Its goal is to produce policy-neutral reports that inform policymakers about the best thinking of the scientific community. These reports have tremendous impact on the debate, owing to the credibility of the IPCC process.
The IPCC is actually split into three working groups. Working group 1 focuses on basic climate science, working group 2 focuses on the impacts of climate change and human adaptation to it, and working group 3 focuses on mitigation efforts (efforts to reduce carbon dioxide emissions). In 2007, as part of the IPCC's fourth assessment report, each of the three working groups issued a report (e.g., see here for a discussion of the working group 1 report).
Now comes the final part of the fourth assessment report: the synthesis report. This report ties together the three working group reports in an effort to create a single unified picture of what we know about climate change.
