When Hotspots Get Too Hot
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.
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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