In the three years since the first edition of this book appeared, events related to climate change have moved rapidly. The fourth IPCC assessment report has documented the continued strengthening of scientific evidence for climate change, its predominant human causes, and the likely rate and risks of continuing changes. The Stern Review and subsequent debate have provoked a more serious discussion of the long-run character of climate-change risks and the appropriate way to evaluate them. The Kyoto Protocol first commitment period has arrived with many nations failing to meet their commitments, even as discussions starting in Bali in 2007 and continuing through Copenhagen in 2009 have sought to re-energize international actions. The United States has re-engaged with international efforts to build an effective response to climate change. And significant policy initiatives have been advanced by many nations, including comprehensive climate and energy legislation being considered in the US Congress. The accumulation of these events required this rewriting, even if continued rapid movement of climate-change policy and politics may mean that the summary of recent events in this edition will also have a short shelf-life.

But not everything about climate change moves fast. On the contrary, many key elements of the issue have changed little since we wrote the first edition. Although climate has many layers of variation on multiple time-scales, the basic dynamics of greenhouse-gas driven climate change operate on time-scales of decades and longer.