(This review was Published in Ecological Restoration Volume 31, Number 1, March 2013, pp. 99-100)
(Copyright by the journal 2013; all rights reserved)
Having begun research on possible ecological effects of global warming in 1968 and developing one the first major methods to forecast such effects on forests, I looked forward to reviewing Saving a Million Species, because Lee Hannah, the book’s editor, writes that the book’s purpose is to deter- mine “what is the extinction risk associated with climate change, and how many species may perish,” and that the book “addresses this important question by synthesizing the [scientific] literature” (p.3). But of course an edited book with 20 chapters and 31 authors is a mixed bag.
The book is divided into six sections: Introduction; Refining First Estimates; Current Extinctions; Evidence from the Past; Predicting Future Extinctions; and Con- servation Implications. The four chapters in “Evidence from the Past” are excellent, the data are recent, evidence is advancing rapidly, and the analysis is careful and objec- tive, therefore helpful in thinking about current climate change. For example, in “Terrestrial Ecosystem Response to Climate Change during the Paleogene,” authors Wil- liam C. Clyde and Rebecca LeCain discuss the dramatic Paleocene-Eocene Thermal Maximum (PETM), a warm- ing that occurred about 55 million years ago. They write: “Migration was an important coping mechanism for both mammal and plant taxa during the PETM. Mammals appear to have exhibited more community coherence . . . whereas plant taxa seem to have reacted more indi- vidualistically. This increased dispersal activity did lead to high extinction rates in most cases but not necessarily to lower diversity, given the offsetting effects of increased origination rates.”
The book’s first sections consider recent computer fore- casting of possible biodiversity effects of global warming, dealing primarily with two of the four methods commonly in use today for these forecasts: climate envelope and species-area curve models, paying less attention to two other kinds of models: those in which individual species are the units of interest and those that directly integrate biodiversity within a general circulation (global climate) model.
One of the best of these chapters is “The Use and Misuse of Species-Area Relationships in Predicting Climate-Driven Extinctions.” Authors John Harte and Justin Kitzes care- fully analyze the theoretical limitations of this method, noting that “numerous conceptual and practical prob- lems permeate this seemingly solid and straightforward approach.” But they pay little attention to a primary failing of this method, which is that the data on which this method depends are crude at best and often lacking. For example, the best-known of the papers using this method, Thomas et al. (2004), concluded that the area of the boreal forest would decline 4%. But an empirical study of the biomass stored in the boreal forest of North America showed that botanical maps of the North American forests differed by a factor of two—200% in the area defined as boreal forest, eclipsing the forecast loss of 4%, and the estimate of biomass had a 95% confidence interval of more than 20% (Botkin and Simpson 1990). Therefore a forecast loss of 4% means little.
Climate envelope models, currently popular, are dis- cussed in several chapters, without sufficient discussion of their fundamental limitations. These overlay the current distribution of a species or group of species on a current climate map (usually just temperature isotherms), typically represented as a box representing the biodiversity range. Then the box representing the biodiversity group is overlaid on a map of a forecasted change in climate. Among the imbedded assumptions are that the current biota distribution is in a steady state with the current climate, and that a single climate variable is sufficient to represent the entire causes of biota distribution.
The difficulties climate envelope models face are made clear by the history of Kirtland’s warbler, the first songbird in the U.S. to be subjected to an annual monitoring that was a complete census. Ornithologists were shocked to discover that the population dropped by half in the first decade of this annual census. This warbler was known to nest in a very limited area in southern Michigan. Com- parison of the nesting area with the climatic limits would yield a forecast based on climatic envelope models of a very limited potential range. It was believed that the warbler was stuck in this limited area, probably because it nested only in young jack pine trees that grew on one highly local- ized soil, a very sandy soil. However, recently Kirtland’s warbler males have been heard singing in Wisconsin, a good distance from the supposed fixed and unchangeable habitat range. (For a forecast of the possible effects of global warming on this species, see Botkin et al. 1991).
More important, contrary to the editor’s assertion, Saving a Million Species does not synthesize all of the scientific literature on these methods. It focuses instead on a subset limited primarily to publications since 2002 by scientists who agreed that anthropogenically induced global warming is unquestionably real and will cause major biodiversity disasters, rather than considering the full range of scientific possibilities for climate in the future.
In sum, the book is worthwhile for its review of climate and extinctions in the fossil record alone, and for some of the chapters such as the fifth, “The Use and Misuse of Species-Area Relationships in Predicting Climate-Driven Extinction,” by John Harte and Justin Kitzes. However, fundamental limitation of the book has to do with what has happened to the scientific debate over global warming and its possible environmental effects. We all know that this has become one of the most contentious and ideologically and politically partisan “scientific” issues of recent times. More than anything else, what is needed today is an objective discussion of the entire range of scientific and statistically valid publications, integrating all viewpoints. But reading this book, it becomes clear that the title gives away the editor’s prejudice. If Saving a Million Species assumes, as it seems to, that these are threatened overwhelmingly by global warming and that forecasts supporting this in gen- eral correct, then the book fails, in total, to provide that much-needed objective analysis.
Botkin, D.B. and L. Simpson. 1990. Biomass of the North American boreal forest: A step toward accurate global measures. Biogeochemistry 9:161–174.
Botkin, D.B., D.A. Woodby and R.A. Nisbet. 1991. Kirtland’s warbler habitats: A possible early indicator of climatic warming. Biological Conservation 56:63–78.
Thomas, C.D.A.C., R.E. Green, Michel Bakkenes, L.J. Beaumont, Y.C. Collingham, B.F.N. Erasmus, M.F. de Siqueira, A. Grainger, L. Hannah, L. Hughes, B. Huntley,
A.S. van Jaarsveld, G.F. Midgley, L. Miles, M.A. Ortega- Huerta, A.T. Peterson, O.L. Phillips and S.E. Williams. 2004. Extinction risk from climate change. Nature 427:145–148.
Dr. Daniel Botkin