Global Warming, Climate Changes May Make Mass Extinction Unavoidable

San Francisco, Calif. ? Worldwide efforts to protect plant and animal species may not be enough to avoid a mass extinction in the face of unexpected climate changes and global warming, says a University of Arizona geoscientist.

While the Earth’s climate is never stable, natural records of the past?such as fossils, ice cores, corals, and lake sediments?reveal that the species and ecosystems of today evolved within a specific range of climate conditions, says Jonathan Overpeck, a professor of geosciences and director of the UA Institute for the Study of Planet Earth.

Overpeck, along with Cathy Whitlock from the University of Oregon and Brian Huntley at the University of Durham in the United Kingdom, reviewed the last decade of paleoclimate work for clues to how future climate change may affect the biosphere. Their work appears as a chapter in the recently published book “Paleoclimate, Global Change, and the Future” (Springer, November 2002).

The authors are concerned that human activities, such as increased carbon dioxide emissions into the atmosphere, may push the climate outside of its current range, with devastating impacts on species around the globe.

“They evolved under this set of conditions, but now we’re going to throw things at them that they’ve never seen before,” Overpeck said recently at the American Geophysical Union meeting in San Francisco.

The Intergovernmental Panel on Climate Change predicts global temperatures will rise 3 to 10 degrees Fahrenheit by the end of the century.

“We’re talking about an amount of warming that could equal or be greater than the warming from the last glaciation,” Overpeck says. “But we’re going to do it in 100 years rather than over many centuries.”

Many conservation efforts focus on parks and natural preserves to protect species from expanding development, pollution, deforestation, and other human impacts on the environment. In 2000, British ecologist Norman Myers and colleagues identified 25 “biodiversity hotspots” around the world as priorities for conservation planning. These areas comprise only 1.4 percent of the Earth’s land surface, but include as many as 44 percent of all plant species and 35 percent of land vertebrates.

“Their hypothesis is that if we put the most resources into these hotspots then we can avert mass extinction,” Overpeck says.

While such efforts are likely necessary, Overpeck believes they alone won’t be sufficient to stop the 6th major extinction in the Earth’s history. He says the planet could lose more than 50 percent of its species by 2150 if nothing is done to slow global climate change.

One reason is that most species won’t be able to keep up with the rapid rate of climate change, Overpeck notes. A warmer climate could change the natural habitat range for many species, requiring them to migrate to new areas or adapt to new conditions.

Previous studies have shown that most species can expand their range between 200 and 2,000 meters per year (600 to 6,600 feet). In order to keep up with the climate change predicted for the next century species ranges would have to change at rates up to 10,000 meters (33,000 feet) each year?as much as 50 times faster.

Focusing conservation on natural preserves and parks may also limit the ability of species to adapt, Overpeck says. The plants and animals in each of the “hotspots” will have nowhere to migrate if climate change shifts their natural range. The strategy will also limit the genetic diversity within species.

“Genetic diversity is the insurance that species and ecosystems have against climate change,” Overpeck says.

Even in the absence of global warming, many of the biodiversity hotspots would still be vulnerable to abrupt climate changes, such as droughts, floods, and tropical storms, Overpeck says.

For example, paleorecords show that the hotspot region in West Africa has been vulnerable to decade-long “mega” droughts in the past. Coastal hotspots such as the Caribbean and south Florida are susceptible to abrupt shifts in hurricane frequency and sea level rise, as well as other sudden climate changes.

“You add in abrupt change and the odds of us being able to save the majority of species on Earth go way down,” Overpeck says.

These types of abrupt shifts are difficult to predict or plan for, Overpeck says. To make matters worse, he adds, global warming will likely increase the odds of abrupt shifts happening in the future.

Beefing up conservation efforts?such as having redundant preserves and creating corridors for plants and animals to migrate?will help protect species, he says, but ultimately won’t be enough if carbon dioxide emissions aren’t reduced.

“We’re stacking the odds against biodiversity if we allow human-caused climate change to continue unabated.”

ACCOMPANYING ART: Biodiversity Hotspot Map
CAPTION: Based on the original biodiversity map created by Norman Myers, this annotated version shows hotspot regions where abrupt climate shifts occurred in the past. Areas labeled “DD” are known to have experienced megadroughts lasting a decade or longer. Those labeled “HT” have been susceptible to abrupt shifts in hurricane frequency. Overpeck notes that the other hotspot regions may also be vulnerable to abrupt climate shifts, but detailed paleo-climate data are lacking from these areas.

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