John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Losses will accelerate the hotter the planet gets, according to new research.
As the planet continues to warm up like a Turkish bath, how many kinds of animals can we expect to perish?
Scientists have estimated a loss of anywhere from 0 to 54 percent of all species, according to Mark Urban, a biologist at the University of Connecticut. That's an astoundingly broad range, and not really helpful for preparing conservation strategies. So Urban did a meta-analysis of more than a hundred biodiversity studies and tightened the boundaries. In a new paper in Science, he reports that climate-induced extinctions could fall upon as little as 2.8 percent or as much as 16 percent of species.
Extinctions will accelerate the hotter the planet gets, says Urban. His low estimate comes from a scenario where warming peaks and declines by 2100—something that's almost definitely not going to happen. The highest prediction of 16 percent loss assumes temperatures will rise by 4.3 degrees Celsius this century, a severe scenario that some scientists nevertheless believe could happen.
Die-offs are likely to hit hardest among endemic species, aka ones isolated to a narrow range by human encroachment or geography (say, an island). The highest-risk animals live in Australia, New Zealand, and throughout South America, and include many reptiles and amphibians. And those that won't fall off the face of the planet could still face hardship.
"Even species not threatened directly by extinction could experience substantial changes in abundances, distributions, and species interactions, which in turn could affect ecosystems and their services to humans," writes Urban. "Already, changes in species’ phenologies, range margins, and abundances are evident." If you don't believe that, you haven't heard of Italy's shrinking goats, Argentina's dying penguins, or bleached corals around the world.
Here's Urban's grim conclusion:
In 1981, [James] Hansen and colleagues predicted that the signal of global climate change would soon emerge from the stochastic noise of weather. Thirty years later, we are reaching a similar threshold for the effects of climate change on biodiversity. Extinction risks from climate change are expected not only to increase but to accelerate for every degree rise in global temperatures. The signal of climate change-induced extinctions will become increasingly apparent if we do not act now to limit future climate change.