Local extinctions are increasing as the warming progresses
Surprising Number of Species Going Extinct in Their Usual Homes, Study Says
InsideClimateNews.org, Dec. 2016
As species struggle to move to adapt to climate change, many are disappearing from the warmest parts of their usual range, research shows.
Hundreds of species around the world—plants, animals, marine life—are experiencing local extinctions due to climate change, according to a new study. Researchers say it's likely to be just the beginning.
As the climate warms, these species, which range from types of chipmunks to grasses to sea snails, are no longer showing up in the places they used to call home. The phenomenon isn't isolated to one particular geographical region or temperature zone, the study found.
Of the 976 species analyzed in the study, which was published Thursday in the journal PLoS Biology, nearly 50 percent have already become extinct along the "warm edge" of their range. It's a reflection of a known process, by which species are moving poleward and to higher altitudes to escape changes to their habitats as the climate warms. The study's author, John J. Wiens, said local extinctions are inherent in range shifts.
The species being impacted can't exactly say, "'Oh, it's too hot here, I'm heading north,'" said Wiens, who is an ecologist and evolutionary biologist at the University of Arizona.
The species have three choices: Adapt to the changing temperature, emigrate or die.
Wiens analyzed other research that assessed range shifts for other species, looking for patterns. What he found surprised him.
"The overall striking pattern is how similar it is," he said, pointing out that it's not just 50 percent of tropical amphibians, or 50 percent of temperate marine species that are going locally extinct. "It's about 50 percent all over the world and for all these different groups of organisms."
Since 1880, the world's climate has warmed 1.7 degrees Fahrenheit, according to NASA. But that hardly compares to what's in store. The National Climate Assessment outlines a best-case scenario for global warming that raises temperatures 2.5 degrees Fahrenheit above the average from 1901-1960 by the end of the century, and that can only be accomplished with aggressive policies and regulations. The business-as-usual scenario results in 8 degrees of warming by the end of the century, and it could go as high as 11 degrees.
Though species have adapted throughout history as the climate has shifted, the difference now is the pace of change. It's happening so quickly, species don't have enough time to change along with their changing habitats.
"We do a lot of work that's projecting into the future," said Chad Wilsey, the director of conservation science for the National Audubon Society. "But climate change has been going on certainly in the last 40 years, and we can already document those impacts."
Wilsey, who has studied climate-driven species range shifts among birds and other species, reviewed Wiens' study internally for Audubon. Wilsey said it was an important overview, but cautioned that his small sample size makes any sweeping conclusions difficult. That said, Wilsey said he expects that science will reaffirm Wiens' work. "I think over time we will have more evidence that confirms this initial review of studies," he said. "I actually think that a pattern exists. It's real."
Jennifer Sunday, a climate change ecologist at the University of British Columbia, also said that the small sample size is limiting. "Some of these data, once he breaks them down, some categories have just one study touching on it," she said. "It might be a little early to be teasing out some of these comparisons."
Sunday did find Wiens' methods compelling. To find the studies to include in his survey, Wiens searched for work that dealt with range contractions, rather than seeking out studies that dealt specifically with the term "local extinction." That allowed him to cast a wider net and hopefully avoid publication bias.
Though the study found that local extinctions were happening worldwide and across species, it did find a higher rate of local extinction among species in tropical and subtropical zones. Wiens explained this by highlighting a study that contrasted elevations in Costa Rica and Colorado. In Colorado, it's hot in the summer and cold in the winter. Thus, species are more able to adapt, because they have evolved to do so. In the tropics, however, temperatures do not vary much between seasons, so species are less prepared to adapt to changes. "That's bad news when climate changes rapidly," said Wiens.
"There have been a lot of predictions about extinctions. What I take away from this is that those are already happening. They're already really widespread all over the world, but the amount of climate change that has happened is actually really small relative to what we're expecting."