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When Hotspots Get Too Hot

Norman Myers

Climate Change and Biodiversity. Edited by Thomas E. Lovejoy and Lee Hannah. xiv + 418 pp. Yale University Press, 2005. $65.

Much has been made of the idea that the principal agents in the mass extinction now under way are the slash-and-burn "shifting cultivators"—small farmers who torch huge blocks of tropical forest each year. The forests harbor at least half or maybe even three-quarters of all terrestrial species, and they are being eliminated faster than any other biome. That the sole remaining habitats of thousands of species each year are thus being destroyed does not mean that the species become extinct forthwith; mostly they don't. They may hang on for decades, but their final refuges will ultimately prove too small to maintain such key factors for survival as sufficient genetic variability. So after decades of last-gasp existence as "living dead," they eventually succumb.

The plant shown in the inset is Vexatorella amoena...Click to Enlarge Image

It now turns out, as we learn in Climate Change and Biodiversity, that another great eliminator of species is at work: the people who burn fossil fuels and thus contribute to the buildup of carbon dioxide in the atmosphere and hence to global warming. Scientists anticipate that climate change on a grand scale will alter entire biomes, degrading and otherwise depleting them. Consider, for instance, two sectors of South Africa that feature such exceptional concentrations of species that they qualify as global epicenters ("hotspots") of biodiversity: The Cape Floristic Region contains the sole remaining habitats of 6,210 plant species (almost one-third as many as in the United States), and the Succulent Karoo harbors 2,439 endemic plant species. In a globally warmed world with just 2 degrees Celsius of increased temperature, these two hotspots might well lose between one-third and one-half, perhaps even more, of their present vegetation.

It is roughly reckoned that when an endemic plant species becomes extinct, it takes with it between 10 and 30 endemic animal species. In just these two areas, which have a total expanse of a mere 45,500 square kilometers and are thus no bigger than Vermont and New Hampshire put together, we can expect a mini-mass extinction within the next few decades—supposing, of course, that we continue doing all too little to curb global warming processes.

The editors of Climate Change and Biodiversity, Thomas E. Lovejoy and Lee Hannah, assert in their preface that "It is now clear that climate change is the major new threat that will confront biodiversity this century." The burning of fossil fuels, if it is not restricted, may eventually impose at least as many extinctions as most other causes put together. That, at least, is the startling conclusion that can be drawn from reading the book, which tackles what surely ranks as the single most pressing issue of our time. After all, a mass extinction that overtook the most species-rich areas in the world would be the biggest such spasm since the dinosaurs and their associates were driven over the edge 65 million years ago. Worse, it would take evolution several million years to restore the damage by generating replacement species with numbers and variety to match today's. Indeed we live in interesting times.

Not that climate change should be considered in isolation, however much it is coming to rank as the number one phenomenon in the mass extinction arena. It will interact with, and its impact will be compounded by, parallel disruptions from habitat fragmentation through other causes. Pollution and a slew of other environmental problems that are detailed in chapter after chapter of this book will also have impoverishing repercussions. All of these factors will reinforce one another, so that their effects will be multiplicative rather than merely additive. This dimension of the biotic crisis makes global warming the biggest threat we face. Although other sources of mass extinction are important, this "driver of drivers" is in a league of its own.

All of this contrasts with certain traditionalist approaches of conservation biology, which evaluates threats in terms of discrete factors such as adverse ecological and life-history attributes (for example, rarity, endemism and very localized distribution). As this book's articles demonstrate, it is more revealing to consider the synergies at work. For instance, a few species feature "slow" life histories because they are large-bodied, mature late and live a long time. Examples include elephants, whales and redwood trees. If these same species also have specialized habitat needs, such as assured food supplies, they face a much greater risk of extinction.

The most admirable feature of this book, then, is that its chapters address a spectrum of issues within a single conceptual framework. Topics covered include climate modeling and projections (also "backcasting" assessments), recent evolutionary effects of climate change, and the adaptive responses of biotas both present and prospective. In particular, the articles contributed by Terry Root, Chris Thomas, Lesley Hughes and Camille Parmesan offer conclusive evidence that many plants and animals are already reacting to climate change by altering their distributions, phenologies and genetic structures.

Other issues discussed in the book include practical questions, such as how to design landscapes and seascapes in response to climate change and how to manage protected areas in ways that reduce the damage of global warming. Consider the outlook, cited above, for the Cape Floristic Region. In a globally warmed world, temperature bands will tend to migrate away from the equator and toward the poles. Vegetation communities will need to follow suit as best they can, albeit at a speed perhaps 10 times greater than that necessitated by the vicissitudes of climate during the late Pleistocene. In principle, the vegetation communities of, say, Florida could migrate northward toward the Carolinas, although to do so they would have to traverse a "development desert" of farmlands and urban settlements. The vegetation communities of the Cape Floristic Region will seek to migrate southward—but to the south lies only the ocean. Similar roadblocks will be encountered in at least one-third of the world's 34 biodiversity hotspots. True, certain vegetation communities could seek refuge by migrating up such mountains as are available, but opportunities for escape of this sort will often be limited at best.

The book reflects the aggregate expertise of 66 leading scientists, notably environmental biologists and evolutionary ecologists, drawn from academia, agencies and nongovernmental organizations. The contributors summarize the evidence for climate change, assess what it means for biodiversity, discuss trends and consider what action conservation biologists and policy makers should take. Two recommendations are made: to integrate the climate change phenomenon more systematically (and systemically) into conservation responses writ large, and to contribute more vociferously to those many organizations that seek both to restrict and to adapt to climate change.

Conversely, as long as we largely persist with "business as usual"—that is, doing all too little to reduce climate change and its impacts—we are essentially saying that the consequences for biodiversity are such that we can pretty well ignore them. That, at least, is the implicit message that certain "sit on your hands" scientists are sending out to policy makers and political leaders as well as the public at large. This book will go far to modify that message—and, let us earnestly hope, will generate even more bang than its predecessor volume, Global Warming and Biological Diversity, coedited by Lovejoy with Robert L. Peters (Yale University Press, 1992).

It is fitting to end this review with a note on the global warming role of the United States. With 4.5 percent of the world's population, the nation accounts for 25 percent of the world's carbon dioxide emissions. President George W. Bush claims that the Kyoto Protocol and other efforts to curb carbon dioxide emissions would wreck the American economy, given how strongly it is based on fossil fuels. He should consider that the economy will surely suffer far greater injury through global warming. He might also note that in the view of several front-rank American economists, an attack on global warming could actually boost the American economy through greater emphasis on energy efficiency. By getting more work from every last drop of oil (there is huge scope for improvement, as Japanese achievements attest), U.S. industry could do much to save the world's biodiversity.

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