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Global Warming Found to Displace Species
January 2, 2003
By ANDREW C. REVKIN
Global warming is forcing species around the world, from
California starfish to Alpine herbs, to move into new
ranges or alter habits in ways that could disrupt
ecosystems, two groups of researchers say.
The two new studies, by teams at the University of Texas,
Wesleyan, Stanford and elsewhere, are reported in today's
issue of the journal Nature. Experts not associated with
the studies say they provide the clearest portrait yet of a
biological world driven into accelerating flux by warming
caused at least in part by human activity.
Plants and animals have always had to adjust to shifting
climates. But climate is changing faster now than in recent
millenniums, and many scientists attribute the pace to
rising concentrations of heat-trapping greenhouse gases.
In some cases, species' ranges have shifted 60 miles or
more in recent decades, mainly toward the poles, according
to the new analyses. In others, the timing of egg laying,
migrations and the like has shifted weeks earlier in the
year, creating the potential to separate species, in both
time and place, from their needed sources of food.
One academic not associated with the studies, Dr. Richard
P. Alley, an expert on past climate shifts who teaches at
Pennsylvania State University, said that climate had
changed more abruptly a few times since the last ice age
and that nature had shifted in response. But, he noted,
"the preindustrial migrations were made without having to
worry about cornfields, parking lots and Interstates."
Citing the new work and studies of past climate shifts, Dr.
Alley saw particular significance in the expectation that
animals and plants that rely on one another were likely to
migrate at different rates. Referring to affected species,
he said, "You'll have to change what you eat, or rely on
fewer things to eat, or travel farther to eat, all of which
The result in coming decades could be substantial
ecological disruption, local losses of wildlife and
extinction of some species, the two studies said.
The authors express their findings with a certainty far
greater than in the last decade, when many of the same
researchers contributed to reports on biological effects of
warming that were published by the Intergovernmental Panel
on Climate Change, the top international research group on
The authors of one of the new Nature papers, Dr. Camille
Parmesan, a biologist at the University of Texas, and Dr.
Gary Yohe, an economist at Wesleyan University, calculated
that many ecological changes measured in recent decades had
a 95 percent chance of being a result of climate warming
and not some other factor.
"You're seeing the impact of climate on natural systems
now," Dr. Yohe said. "It's really important to take that
Some butterflies have shifted northward in Europe by 30 to
60 miles or more, with the changes closely matching those
in average warm-season temperatures, Dr. Parmesan said. The
researchers were able to rule out other factors - habitat
destruction, for example - as causes of the changes.
Some of these changes meshed tightly with variations in
temperature over time. Dr. Parmesan cited bird studies in
Britain. There, populations of the great tit adjusted their
egg laying earlier or later as climate warmed early in the
20th century, then cooled in midcentury and warmed even
more sharply after the 1970's.
Over all, Dr. Parmesan's study found that species' ranges
were tending to shift toward the poles at some four miles a
decade and that spring events, like egg laying or trees'
flowering, were shifting 2.3 days earlier a decade.
Around Monterey Bay in California, warmer waters have
caused many invertebrates to shift northward, driving some
species out of the bay and allowing others to move in from
Authors of both new papers said they were concerned that
such significant ecological changes had already been
detected even though global temperatures had risen only
about one degree in the last century.
They noted that projections of global warming by 2100
ranged from 2.5 to 10 degrees above current levels, should
concentrations of carbon dioxide and other heat-trapping
gases, which flow mainly from smokestacks and tailpipes,
continue to rise.
By comparison, the world took some 18,000 years to climb
out of the depths of the last ice age and warm some five to
nine degrees to current conditions.
"If we're already seeing such dramatic changes" among
species, "it's really pretty frightening to think what we
might see in the next 100 years," said Dr. Terry L. Root,
an ecologist at Stanford University who was the lead author
of one of the new studies.
The two teams of researchers used different statistical
methods to analyze data on hundreds of species, focusing
mainly on plants and animals that have been carefully
studied for many decades, like trees, butterflies and
birds. Both teams found, with very high certainty, a clear
ecological effect of rising temperatures.
Several of the researchers said the effects of other,
simultaneous human actions, like urban expansion and the
introduction of invasive species, could greatly amplify the
effects of climate change.
For example, the quino checkerspot butterfly, an endangered
species with a small range in northern Mexico and Southern
California, is being pushed out of Mexico by higher
temperatures while also being pushed south by growing
suburban sprawl around Los Angeles and San Diego, Dr.
"The butterfly is caught between these two major human
factors - urbanization in the north and warming in the
south," said Dr. Parmesan, who has spent years studying
shifting ranges of various checkerspot species.
Dr. Alley said the studies illustrated the importance of
conducting much more research to anticipate impending harms
and devise ways to maintain biological diversity, for
instance with green "wildlife corridors" linking adjacent
pockets of habitat.
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