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interesting but not convincing
on July 23, 2010
The Great Global Warming Blunder attempts to show that anthropogenic (human-caused) greenhouse gas emissions are not the principal cause of recent global warming and won't warm Earth much in the future. Judging by other reviews of this book, readers who have already made up their mind against anthropogenic global warming (AGW) will find this book highly convincing. I think the book has some good points to make but in the end some of its claims undercut its credibility.
A central thesis of the book is that something called the Pacific Decadal Oscillation changes the average cloudiness of the Earth from decade to decade and that this accounts for global warming. A simple (1 equation) model predicts how surface temperature might respond to surface cloudiness and other factors. Dr. Spencer runs this model with about 100,000 combinations of different values for 4 parameters and chooses the parameters which make the model results look most like changes in 20th century observed temperature. It's strange to engage in such an obvious exercise in curve fitting, especially when AGW "skeptics" often criticize much less arbitrary climate models. But it gets worse. The main "success" of this model is to follow the warming trend in the first half of the 20th century. This happens because the model has a tendency to bring the temperature back to an equilibrium temperature, and the model temperature is initialized for year 1900 at .6 C below an equilibrium which is set to near mid-20th century values. Thus most of the model's "global warming" is just a recovery from this arbitrary start point. The book offers no justification for this choice, probably because there is none. For the 2nd half of the twentieth century, the model prediction only slightly resembles observations. U. Chicago climate scientist Ray Pierrehumbert has a more detailed critique of this model on the realclimate website.
Another thesis of the book is that the climate system is much less sensitive to greenhouse gases than models show. There is great uncertainty in climate sensitivity, and so this claim may turn out to be true. Again, I was not convinced; the specific analysis technique was not very well explained. Spencer has a published paper on this topic, but the paper does not make as sweeping claims as the book. The data presented in the book shows much larger scatter than at least one paper that Spencer's paper cites (Forster and Gregory, 2006, J. Climate), making me wonder if the low sensitivity Spencer finds is an artifact of taking relatively noisy monthly data rather than less noisy annual data as in Forster and Gregory.
The book has some nice discussions for the non-specialist of how climate works, and raises some good questions about AGW. I appreciate that Spencer concentrates on a few scientifically defensible critiques of AGW and tries (with mixed results) to resist the urge to demonize scientists with an opposing view.
Still, Spencer shows a typical credulity about alternatives to AGW which is unbecoming a "skeptic." Showing that AGW is not definitively proved is different than showing an alternative view is proved. On several topics, the book cites papers suggesting AGW is minor while ignoring papers supporting AGW. Spencer spent a long time arguing that satellite data proved there was no global warming, until other groups showed that his data analysis had an error which incorrectly eliminated the trend (see the journal Science, 11 Nov 2005). He argues that AGW proponents are biased by their own desire to save the world, but I wonder about Spencer's own biases. The book describes how Al Gore's testimony on global warming uses typical "propaganda" techniques of persuasion, while ignoring similar or worse techniques among political critics of AGW. He complains about the lock modelers supposedly have on climate science, but he uses satellite data that cost billions of dollars to collect.
The book finishes with familiar and generally unsupported statements that a rapid move to less polluting energy use will hurt the poor, that more CO2 may be better for life on Earth, and that we don't know much about ocean acidification but we shouldn't worry about it. Readers will be irritated or gladdened by this part, depending on their politics, but won't learn much new from these statements.