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Scientists know climate change will cause extinctions, but just how many species might disappear in a warmer world has been harder to pin down. A new study out today tries to estimate how much of Earth's biodiversity is threatened under different climate futures and which species are especially at risk. NPR's Jonathan Lambert has more.
JONATHAN LAMBERT, BYLINE: To think about how climate change might threaten a given species, imagine a tiny mountain bird that eats the berries of a particular tree. That tree can only grow in a narrow elevation band around the mountain, where it's adapted to the microclimate. But as global temperatures rise, both the tree and the bird will be forced to rise, too, tracking their microclimate as it moves up the mountain. Eventually, says biologist Mark Urban...
MARK URBAN: They reach the peak, and then there's nowhere else to go.
LAMBERT: Scientists call this the escalator to extinction, and it's just one way climate change is already squeezing plants and animals out of their habitats. Decades' worth of studies have projected that climate change could impact different species in a variety of ways, some good and some bad. In a new analysis published in the journal Science, Urban tried to bring it all together.
URBAN: What I wanted to do was to get a better overall picture across all those studies and across the globe and really to be able to provide an answer to decision-makers who wanted to know exactly how climate change would translate into extinction risk.
LAMBERT: Urban is with the University of Connecticut and looked at nearly 500 studies to figure out how many more species would be threatened with extinction by the end of the century for every additional degree of warming. Overall, he says the picture is worrisome.
URBAN: Where we are now - and we're experiencing already close to 1.5 degree Celsius - that would translate into about 1.8% extinction risk for species around the world. However, if we start to increase the temperature beyond that, then we start to see an accelerating risk.
LAMBERT: If emissions continue at their current trajectory, Urban estimates about 1 in 20 species would be at risk of extinction. Warm up a bit more to four or five degrees, and as many as 30% of species are in trouble.
CHRISTIAN ROMAN-PALACIOS: That 30% could be the best-case scenario among the worst-case scenario, so it could be even worse than that.
LAMBERT: Christian Roman-Palacios is a biologist with the University of Arizona. He says there's a lot people don't know about how species will react to higher temperatures. Plants and animals may be less able to cope than researchers assume, or ecosystems could lose so many species that they just start to collapse. Given those risks, John Wiens, also with the University of Arizona, says big, global solutions like reducing greenhouse gas emissions are required.
JOHN WIENS: What's sort of awful about climate change is, you know, say you stop all the destruction of rainforests and other tropical habitats, you know, get everything into preserves, and you could still lose, you know, one-third of the species on Earth due to climate change. It's really hard to sort of protect species on the ground from it.
LAMBERT: The study says amphibians and species that live on mountains and islands are most at risk. Focusing conservation efforts there could help, but Urban says those measures are no substitute for reducing emissions to preserve biodiversity.
URBAN: Each of these species has encountered and solved life's problems, and so they're really the great books of knowledge on Earth. And we really don't want to burn those books before we get a chance to read them.
LAMBERT: Jonathan Lambert, NPR News.
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