Global Warming Could Cause Mass Extinctions by 2050, Study Says

Brian Handwerk
for National Geographic News
April 12, 2006
A new study suggests that global warming could threaten one-fourth of
the world's plant and vertebrate animal species with extinction by 2050.

The report's authors reached their conclusion after estimating potential changes to habitats—and the resulting loss of species—in 25 biodiversity "hot spots" around the world.

The ecologically rich hot spots include South Africa's Cape Floristic Region, the Caribbean Basin, and the tropical regions of the Andes Mountains. These territories compose only a small fraction of the planet's land area but contain large numbers of Earth's flora and fauna.

"These [hot spots] are the crown jewels of the planet's biodiversity," lead author Jay Malcolm of the University of Toronto told the Canadian Press.

"Unless we get our act together soon, we're looking at committing ourselves to this kind of thing."

The report appears in the current issue of the journal Conservation Biology.

Many Threats Seen

Global warming projections are by nature uncertain, and the report includes many variables that significantly affect species' survival rates both for good and for ill.

Changes to the rate and degree of warming, as well as the ability of species to migrate or adapt, altered the estimates of species' extinction risk.

Climate change is also only one threat to species diversity. Many plants and animals are already feeling the effects of habitat destruction and invasions by non-native species. It is difficult for scientists to take all such factors into account.

Still, the study's worst-case scenarios are sobering.

They include a doubling of present carbon dioxide levels (as predicted by many climatologists) and rising temperatures that could potentially eliminate 56,000 plant and 3,700 animal species in the 25 hot spot regions.

(Read National Geographic magazine's "Global Warning: Signs From Earth.")

The report's findings echo those of a 2004 study, in which a team of international scientists suggested that over a million species—15 to 35 percent of those they studied—could be at risk of extinction by 2050.

Both the 2004 study and the current research were conducted in part by scientists from Conservation International.

"We used a completely different set of methods [from the 2004 study] and came up with similar results," Conservation International's Lee Hannah, co-author of the current study, told Reuters.

"All the evidence shows that there is a very serious problem."

Hot Spot Species Live on the Edge

Stuart Pimm, an expert in extinctions and biodiversity at Duke University in Durham, North Carolina, explained that species living in ecological hot spots are at particular risk when their environments change.

"That's where the most vulnerable species are, because they have the smallest geographical ranges," said Pimm, who is not affiliated with the study.

Species living high on tropical mountainsides, for example, have nowhere to go if temperatures warm their home turf.

In South Africa's Cape Floristic Region, located on the continent's southern tip, species are unable to migrate to lower latitudes to escape the rising temperatures.

"There's no question that the poles are experiencing the greatest climatic change," Pimm said.

But polar species are far fewer in number and may not face the same extinction risk as those that live in more confined hot spots with greater biodiversity.

"While polar bears and caribou are being harmed, they are not as vulnerable as the species that live in these hot spots because of [the hot spot species'] very narrow geographic ranges."

Other experts warn that it's not just the hot spots featured in the new study that face an imminent extinction risk.

"Many species are indeed struggling to hold on in locations all over the globe, not just in hot spots," said biologist Terry Root, of Stanford University's Center for Environmental Science and Policy, who was not involved in the study.

"This is not some activity that will only be occurring 'overseas.' The likely extirpations and extinctions will also be occurring within a couple hundred miles of all of our back yards."

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