As animals and plants move to higher elevations or away from the equator in search of new homes, their historic ranges have shrunk, causing them to go extinct in the areas they left behind.
The study, a meta-analysis of dozens of range shift studies, found that 47% of the 976 species surveyed have experienced local extinctions tied to climate change. That means there are none left in the places where they lived for years.
"This is not based on a future projection, it's based on what's already happened," said study author John Wiens, an evolutionary biologist and ecologist at the University of Arizona.
Since 1880, the average global temperature has increased by about 1.4 degrees Fahrenheit. That's a modest increase compared with the potential 1 to 5 additional degrees of warming the world could see in the next 100 years, the study argues.
With further warming, local extinctions could turn into global ones.
"In some ways, this is just the beginning," he said.
Wiens searched the scientific literature for range shift studies that statistically linked their results to climate change. To be included in the analysis, the study must have monitored the "warm edge" of a species' habitat — the one that's one most likely to experience the effects of global warming first. The study did not need to document a local extinction.
Drawing from 27 studies of 716 animal and 260 plant species on six continents (all except Antarctica), Wiens found 460 cases of local extinctions that have already occurred.
The pattern of extinctions was strikingly similar across the globe, Wiens said. Regardless of the climatic region, habitat or the type of organism, about 50% of species are disappearing from their historic ranges.
The effect was most pronounced in the tropics — out of 504 species surveyed, 55% saw local extinctions. By comparison, among species in temperate regions, 39% of 196 species did.
Tropical plants and animals are more sensitive to climate change because they haven't evolved to deal with big temperature swings from season to season. That means organisms living in a particular place are specialized to living within a narrow range of temperatures.
The study also found extinctions were significantly more common among animals and birds than plants. Freshwater fish were particularly vulnerable, since droughts have a tendency to dry up their habitats.
In a 2008 study in Science included in Wiens’ analysis, UC Berkeley biologists Craig Moritz and James Patton found over a dozen small mammal species in
University of Connecticut ecologist and ornithologist Morgan Tingley, whose research on birds in the Sierra Nevada was included in the analysis, credited Wiens' study for highlighting an aspect of range shifts that are often overlooked: the fact that they're indicators of extinctions.
In 2012, Tingley and colleagues recorded range shifts in birds found throughout the California mountain range by comparing historical data from the early 1900s to their own surveys conducted in the 2000s.
He found although many species of birds moved from lower to higher elevations because of warming, others moved downslope because of changes in precipitation. Tingley said climate change could force some species to move away from the upper reaches of their habitats; if so, Wiens' study underestimates the number of species losing ground to climate change.
Tingley said he's most concerned about species that appear to be declining in one area without gaining new habitat to compensate, such as the red-breasted sapsucker of California's conifer and coastal forests. Tingley's research has found that the woodpeckers have gone extinct in the zone that's about 2,500 to 3,300 feet above sea level, but they do not appear to be expanding into higher elevations.
All the species undergoing local extinctions or range contractions are at risk of becoming completely extinct as climate change accelerates. Eventually these species will run out of places to go — they can only climb or migrate so far.
Worse off are the plants and animals on islands or in isolated nature preserves that might not have room to move.
"There's sort of this double jeopardy of habitat destruction and climate change," he said.
To maximize a species' chances of survival, Wiens suggested creating corridors of connected habitat so plants and animals can move from low to high elevations.
However, the best solution, he said, would be to try to curtail global warming.
"Humans are running this experiment with the biosphere: 'Maybe all these species will go extinct, maybe things will be OK,'" he said. "It will be much better if we didn't play this game."
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