Since the Second Edition seven years ago, research and debate on the issue of human-induced Climate change have grown at a rapidly increasing pace. Observations of Climate during this period have provided further information about the warming Earth and there has been substantial improvement in the models that simulate both past and future Climate. Although the main messages regarding the fact of human-induced Climate change and its impact have not changed significantly (on the whole they have been strengthened) more detailed understanding has been achieved regarding the basic science (including the uncertainties), the likely impacts and the imperative for action. Hence the need to update this book.

In 2001 the Intergovernmental Panel on Climate Change (IPCC) published its Third Assessment Report–even more thorough and comprehensive than the first two. As co-chair of the scientific assessment working group for all three of the IPCC reports, I have been privileged to be a part of the IPCC process, which has been so effective in informing the scientific community. Then, through that community, information has been spread to decision makers and others regarding what is known about Climate change with some degree of certainty and also about the areas where there remains much uncertainty. I have leant heavily on the IPCC 2001 Report in revising this text and wish to express my deep gratitude to those many IPCC colleagues with whom I have worked and from whom I have learnt so much.