Global warming, unchecked, could push up to 37 percent of all species toward extinction, study warns

In the first study of its kind, researchers ranging from northern Britain to the wet tropics of northeastern Australia and the Mexican desert said Wednesday that global warming at currently predicted rates will drive 15 to 37 percent of living species toward extinction by mid-century.

Dismayed by their own results, the researchers called for "rapid implementation of technologies" to reduce emissions of greenhouse gases and warned that the scale of extinctions could climb much higher because of mutually reinforcing interactions between climate change and habitat destruction caused by agriculture, invasive species and other factors.

"The mid-range estimate is that 24 percent of plants and animals will be committed to extinction by 2050," said ecologist Chris Thomas, of Britain's University of Leeds. "We're not talking about the occasional extinction -- we're talking about 1.25 million species. It's a massive number."

The study marks the first time scientists have produced a global analysis with concrete estimates of the effect of climate change on habitat. Previous work, much of it by the same researchers, focused on smaller regions or limited numbers of species.

Thomas led a 19-member international team that surveyed habitat decline for 1,103 plant and animal species in five regions: Europe; Queensland, Australia; Mexico's Chihuahua Desert; the Brazilian Amazon; and the Cape Floristic Region at South Africa's southern tip. The study is being published Thursday in the journal Nature.

The five regions encompass 20 percent of the Earth's surface and "include a fair range of terrestrial environments," said Thomas in a telephone interview from Leeds. "Obviously it would be valuable to expand the scope, but there's no reason to think that doing so would change our results tremendously."

Researchers said the wide geographical scope also overcame outside factors that might affect a single region only: "A prolonged drought might cause one instance of a dieback" but be offset by changes elsewhere, acknowledged climate change biologist Lee Hannah, who worked in South Africa. "When you see the broader context, the regional blips drop out."

While there is little dispute that the Earth's temperature is rising, debate over the reasons and speed of change remains contentious. Still, most scientists accept that much of the warming is due to the cumulative effects of human-produced emissions of carbon dioxide and other "greenhouse gases" -- from power plants and other industries -- that trap and hold heat in the atmosphere.

One skeptic, William O'Keefe, president of the George C. Marshall Institute, a conservative science policy organization, raised criticisms of the Nature study, saying the research "ignored species' ability to adapt to higher temperatures" and assumed that technologies will not arise to reduce emissions.

Climatologists have developed models that describe the temperature changes that specific regions have undergone over time periods of as long as 30,000 years. The Nature study used United Nations projections that world average temperatures will rise from 2.5 to 10.4 degrees Fahrenheit by 2100.

The trick for the study, Thomas said, was to marry the maps of projected climate change in particular regions with maps describing the habitat of plants and animals in the same area.

For this, "we needed to get the people together who knew where the species lived," Thomas said. These were the conservationists on the research team -- ecological experts who study extinctions by looking at traditional culprits: destruction of habitat through agriculture, industry or human settlement; invasive species shoving aside native plants and animals; and hunting and extermination of pests.

"Obviously plants and animals depend on climate for survival, but we figured that if we protect them in place, they would be all right," Hannah said in a telephone interview from his home in California. "But now we realize that we have to take care of them not only where they are now, but where they might have to go."

The team calculated the effects of climate change on extinctions by using what ecologists J. Allan Pounds and Robert Puschendorf, in an article accompanying the study, called "one of ecology's few ironclad laws" -- that shrinking habitat supports fewer species.

The study considered a range of possibilities based on the ability of each particular species to move to a more congenial habitat to escape warming. If all species were able to move, or "disperse," the study said, only 15 percent would be irrevocably headed for extinction by 2050; but if no species were able to disperse, the extinction rate could rise as high as 37 percent.