This is the key document on climate change, and from now on you can forget any others you may have read or seen or heard about. This is the one that matters. It is the tightly distilled, peer-reviewed research of several thousand scientists, fully endorsed, without qualification, by all the world's major governments. Its official name is a mouthful: the Policymakers' Summary of the Synthesis Report of the United Nations Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment. So let's just call it The Synthesis.