Climate tipping points loom at 1.5 degrees of warming, new study warns The Earth has already warmed more than 1 degree Celsius. New research suggests that above 1.5 degrees, massive ice melt, ocean current disruptions and coral die-offs are likely.

Humans must limit warming to avoid climate tipping points, new study finds

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ARI SHAPIRO, HOST:

Dramatically cutting greenhouse gas emissions can still help avoid catastrophic climate change, according to new research published today. But NPR's Rebecca Hersher reports irreversible climate tipping points are looming.

REBECCA HERSHER, BYLINE: Climate tipping points are exactly what they sound like - big changes that happen with just a little nudge, like crossing over the center of a seesaw. For example, there's a temperature threshold above which the ice sheet in Greenland will totally melt, no matter what. David McKay is one of the authors of the new study.

DAVID MCKAY: Yes, so if you got to the point that, say, the Greenland ice sheet had passed its threshold and was going to collapse, even if we stopped global warming dead, it would just keep on going for centuries and millennia until the whole thing had collapsed.

HERSHER: The question is, how hot does it need to get to trigger that tipping point? The new study says about 1.5 degrees Celsius of global warming would do it. And other tipping points also become likely around 1.5 degrees of warming - the West Antarctic ice sheet melts away, an ocean current in the North Atlantic stops circulating, most coral reefs completely die.

MCKAY: Most of those have our best estimate. But their tipping point is somewhere around 1.5 degrees.

HERSHER: Right now the Earth is about 1.1 degrees hotter than it was in the late 1800s. So we're just a few tenths of a degree away from 1.5. And 1.5 degrees also has significance in the world of climate change policy. Under the Paris Climate Agreement, countries are trying to limit global warming to between 1.5 and 2 degrees.

MCKAY: And this paper really supports the fact that, yeah, 1.5 isn't just an arbitrary number. It really would reduce the likelihood of these things. Clearly, 1.5 is better than 1.9 or 2 degrees.

HERSHER: The good news is that it's possible to keep global warming to about 1.5 degrees if countries follow through on all their current promises to cut greenhouse gas emissions. But there's basically no wiggle room. Erin Pettit is a climate scientist at Oregon State University who studies ice. She says even if only some of the ice melts, a lot of people will still be in danger.

ERIN PETTIT: We could be several feet of sea level rise just in the next century. So many vulnerable people live on that coastlines and in those flood-prone areas.

HERSHER: And that's the crux of it. It is not too late to avoid runaway climate change, and the next hundred years or so will be increasingly dangerous for a lot of people. Rebecca Hersher, NPR News.

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