Global Warming

Global Warming Threat to 1 in 6 Species

In a study published Thursday in the journal Science, Mark Urban, an ecologist at the University of Connecticut, found that as the planet warms in the future, species will disappear at an accelerating rate.

Global warming has raised the planet’s average surface temperature about 1.5 degrees Fahrenheit since the Industrial Revolution. Species are responding by shifting their ranges.

If emissions of carbon dioxide and other greenhouse gases continue to grow, climate researchers project the world could warm by as much as 8 degrees Fahrenheit. As the climate continues to change, scientists fear, some species won’t be able to find suitable habitats.

For example, the American pika, a hamsterlike mammal that lives on mountains in the West, has been retreating to higher elevations in recent decades. Since the 1990s, some pika populations along the species’ southernmost ranges have vanished.

Hundreds of studies published over the past two decades have yielded a wide range of predictions regarding the number of extinctions that will be caused by global warming. Some have predicted few extinctions, while others have predicted that 50 percent of species face oblivion.

There are many reasons for the wide variation. Some scientists looked only at plants in the Amazon, while others focused on butterflies in Canada. In some cases, researchers assumed just a couple of degrees of warming, while in others they looked at much hotter scenarios. Because scientists rarely were able to say just how quickly a given species might shift ranges, they sometimes produced a range of estimates.

To get a clearer picture, Dr. Urban decided to revisit every climate extinction model ever published. He threw out all the studies that examined just a single species, such as the American pika, on the grounds that these might artificially inflate the result of his meta-analysis. (Scientists often pick out individual species to study because they already suspect they are vulnerable to climate change.)

Dr. Urban ended up with 131 studies examining plants, amphibians, fish, mammals, reptiles and invertebrates spread out across the planet. He re-analyzed all the data in those reports.

Overall, he found that 7.9 percent of species were predicted to become extinct from climate change. Estimates based on low levels of warming yielded much fewer extinctions than hotter scenarios.