University of Connecticut ecologist Mark Urban conducted a meta-analysis of the hundreds of studies published over the last twenty years making predictions about the number of extinctions that global warming might cause. Those predictions, the New York Times reports, have varied widely, from just a few to 50 percent of species worldwide:
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.
Urban filtered that data to its most essential components.
Dr. Urban ended up with 131 studies examining plants, amphibians, fish, mammals, reptiles and invertebrates spread out across the planet. He reanalyzed 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.
By his calculation, with an increase of 3.6 degrees Fahrenheit in surface temperature, 5.2 percent of species would become extinct. At 7.7 degrees, 16 percent would.
Dr. Urban found that the rate of extinctions would not increase steadily, but would accelerate if temperatures rose.
“The loss of one in six species, would be an absolute tragedy, not only because it is sad to lose any part of our rich natural world, but also because biodiversity is fundamental in providing important functions and services, including to humans,” the International Union for Conservation of Nature’s Jamie Carr told the Guardian.
“Such significant changes to biological systems would undoubtedly have knock-on effects, and could potentially result in the collapse of entire systems.”
Still, the situation is not yet completely dire, Urban said. “We still have time. Extinctions can take a long time. There are processes that could be important in mediating these effects, for example evolution, but we really need to very quickly start to understand these risks in a much more sophisticated way.”