Forthcoming in Climate Change: What it means for you, your children, and your grandchildren, edited by Joseph DiMento and Pamela Doughman, MIT Press, expected publication early 2007 2 these doubts have been invoked to justify the American refusal to join the rest of the world in addressing the problem. This book deals with the question of climate change and its future impacts, and by definition predictions are uncertain. People may wonder why we should spend time, effort, and money addressing a

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... problem that may not affect us for years or decades to come. Several chapters in this book have already addressed that question-explaining how some harmful affects are already occurring, how we can assess the likely extent of future harms, and why it is reasonable to act now to prevent a worst-case scenario from coming true. This chapter addresses a different question: Might the scientific consensus be wrong? If the history of science teaches anything, it's humility: there are numerous historical examples where expert opinion turned out to be wrong. At the start of the 20 th century, Max Planck was advised not to go into physics because all the important questions had been answered; medical doctors prescribed arsenic for stomach ailments; and geophysicists were confident that continents could not drift. Moreover, in any scientific community there are always some individuals who depart from generally accepted views, and occasionally they turn out to be right. At present, there is a scientific consensus on global warming, but how do we know it's not wrong? The scientific consensus on climate change Forthcoming in Climate Change: What it means for you, your children, and your grandchildren, edited by Joseph DiMento and Pamela Doughman, MIT Press, expected publication early 2007 3 Let's start with a simple question: What is the scientific consensus on climate change, and how do we know it exists? Scientists do not vote on contested issues, and most scientific questions are far too complex to be answered by a simple yes or no, so how does anyone know what scientists think about global warming? Scientists glean their colleagues' conclusions by reading their results in published scientific literature, listening to presentations at scientific conferences, and discussing data and ideas in the hallways of conference centers, university departments, research institutes, and government agencies. For outsiders, this information is difficult to access: scientific papers and conferences are by experts for experts, and very difficult for outsiders to understand.