Emanuel

Emanuel, Kerry. What We Know About Climate Change. Cambridge, Mass.: The MIT Press,  Boston Review Books, 2007. Pp. xi +85. Hardcover, $14.95.

The book delivers exactly what the title promises, a succinct and readable summary of findings not in dispute plus findings with which most, not all, scientists agree. Some findings not in dispute are that present levels of CO2 are greater than that over at least the last 650,000 years, the earth’s average surface temperature has increased by about 1.2º F in the past century, and that sea level has risen by about 2.7 inches in the last 40 years.  Some findings that most climate scientists agree with are that global mean temperature is now greater than at any time in the past 500 years, that the rise in temperature is due primarily to increasing greenhouse gas concentrations and a leveling off of sulphate aerosols, that sea level will increase 6 to 16 inches in the next century, that rainfall will continue to become concentrated in increasingly heavy but less frequent events, and that both floods and droughts will be more severe.  Although the physics of each of the processes taking place in the atmosphere is generally understood, climate change is very difficult to model, because the various processes interact.  The result is that the relevant equations involve many variables, and the system, at least in the short term, is chaotic.  Weather prediction is a problem of similar complexity but is more tractable because the estimates can be checked with frequent measurements in many places.  Feedback mechanisms, both positive and negative, not clearly understood, could amplify or smooth climate change.  Ice-core records show that climate does not change smoothly in response to fluctuations in solar radiation caused by orbital variation; rather, the climate jumps from one state to another.  Emanuel makes the point that we should be wary of climate changes, especially because we do not understand the mechanism, and that we should make sacrifices now to avoid possible serious consequences.  An After Word by Judith Layzer and William Moomaw asks why the United States is moving so slowly in responding to climate change.  Their argument is that those concerned about the issue have had difficulty up to now in developing a coherent story, while those opposed to addressing the issue have created a coherent story, focused on the uncertainty of some of the scientific questions and on the possibility that the US economy would be harmed if measures were taken.  Layzer and Moomaw point out that the sacrifices required by individuals to decrease global warming are not onerous—if in the future every American who drives 1000 miles a month drove 30 fewer miles the cumulative effect would be sufficient to bring carbon dioxide atmospheric levels back to their present value.  In several places the book makes a case for technological literacy, for an understanding by citizens and government leaders of what causes climate change and what can be done about it.  The book is an admirable example of how to create technological literacy.  All readers would learn much from it and enjoy the experience.