Climate change could eventually claim a sixth of the world’s species

Battling warming. Reducing emissions of soot from vehicles and methane from pipelines may not help reduce rates of global warming as much as earlier studies have suggested, new research suggests.

Ted Spiegel/CORBIS

Up to one-sixth of the species on Earth could disappear if climate change remains on its current course, according to a new analysis of more than 100 smaller studies.

“All the studies are in pretty good agreement: The more warming we have, the more species we’ll lose,” says Dov Sax, a conservation biologist at Brown University who was not involved in the work. “This is really important to know, from a policy viewpoint.”

Industrial emissions of carbon dioxide and other planet-warming greenhouse gases have boosted the global average temperature about 0.8°C (1.44°F) since the beginning of the Industrial Revolution. But studies have disagreed about what impact the rise is having on the world’s species, says Mark Urban, an ecologist at the University of Connecticut, Storrs. Some have estimated that as many as 54% of species could eventually become extinct as a result of climate change, but others have suggested no significant impact.

Such disparate results might stem from the limited nature of some individual studies, possibly because they focused only on a few species or a relatively small geographical region, Urban says. And different teams have often used different methods to come up with their predictions. To address these limits, Urban used statistical methods to help blend the results of previous studies into an apples-to-apples comparison that estimates the risk of extinction for species worldwide.

He chose to analyze only the results of studies that had assessed extinction risks for more than one species, a restriction that narrowed the pool to 131. Then he delved into the details, such as the regions in which the studies had taken place, the types of species considered, whether those species were limited to one small region or were widely dispersed, and whether the species were free to move as climate changed or were blocked by barriers such as mountain ranges, deforestation, or urban development. Finally, he weighted the results of the studies to give more statistical importance to those that assessed extinction risks for larger numbers of species.

Effects of climate change aren’t always immediate, Urban says, and the risks of extinction he’s estimated are the long-term results of species not being able to find suitable habitat. Maybe the habitat will merely shrink to a size that can’t support the species, or maybe it will disappear entirely. In some cases, he notes, a species might not be able to outpace the shift in its range, dying out before it can reach a new homeland. For instance, some plants and animals disperse so slowly over the generations that rapid warming might kill them or their offspring off before they can spread to a suitable new habitat.

At present, about 2.8% of the species on Earth are at risk of extinction due to climate change that has already occurred, Urban says. If the global average temperature rises and then holds at 2°C above the preindustrial average (a level that many scientists think is no longer achievable in view of estimates of future greenhouse gas emissions), then 5.2% might eventually die out. If global temperatures eventually top out at 4.3°C above preindustrial levels, as some studies suggest they will, climate change may ultimately claim one species out of every six, Urban reports online today in Science.

Results of the new study may help researchers and policymakers better assess areas to be set aside for parks and preserves. An area set aside to preserve the species in an ecosystem today may become ecologically unsuitable decades from now, Sax notes, so it’s necessary to think ahead. For example, according to the National Oceanic and Atmospheric Administration, a closely connected group of marine sanctuaries or other protected habitats can create migration corridors for marine life responding to climate change.

Urban “has done a rigorous job of melding the results of these studies,” says Janneke Hille Ris Lambers, an ecologist at the University of Washington, Seattle. The work, she says, also provides an opportunity for scientists to design future studies to fill in current gaps in knowledge. Sax agrees: “We’re just at the beginning of assessing these risks.”