Research: Four key tipping points close to causing higher temperatures

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An international team of scientists looked at 16 climate tipping points — when a warming side effect is irreversible, self-perpetuating and large — and calculated raw temperature thresholds at which they are triggered. None of them are considered likely at current temperatures, although a few are possible. But warming just a few tenths of a degree from now, at 1.5 degrees Celsius (2.7 degrees Fahrenheit) warming since pre-industrial times, puts four in the likely range, according to a study in the journal Science. from Thursday.

The study said a slow but irreversible collapse of the Greenland and West Antarctic ice sheets, a more immediate loss of tropical coral reefs around the world, and the thawing of the high northern permafrost releasing massive amounts of greenhouse gases trapped in the now-frozen land, are four major tipping points. that could be triggered by a warming of 1.5 degrees Celsius, which is three tenths of a degree (half a degree Fahrenheit) warmer than it is now. Current policies and actions put the Earth on a trajectory of about 2.7 degrees Celsius (4.9 degrees Fahrenheit) from warming since pre-industrial times, according to some projections.

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“Let’s hope we’re not right,” said study co-author Tim Lenton, an Earth systems scientist at the University of Exeter in the United Kingdom. “There is a clear chance that some of these tipping points will be inevitable. And that is why it is very important that we think a little more about how we are going to adapt to the consequences.”

Timing matters in two ways for tipping points: when they are triggered and when they cause damage. In many cases, such as ice sheet collapse, they can be activated quickly, but their impact, while inevitable, takes ages to play out, scientists say. A few, such as the loss of coral reefs, cause more damage in just a decade or two.

“It’s a matter of the future generation,” said lead author David Armstrong McKay, a systems scientist at the University of Exeter Earth. “The collapse of the ice sheets is sort of a thousand-year timescale, but it still leaves a very different planet to our descendants.”

The concept of tipping points has been around for more than a decade, but this study goes further and looks at temperature thresholds for when they might be triggered and what impact they would have on people and the Earth. Over the past 15 years or so, “risk levels just kept rising,” Lenton said.

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Lenton likes to think of tipping points as someone leaning back on a folding chair.

“When you start to tip backwards, in that case you have a very simple kind of feedback about gravity that propels you backwards to the splat,” Lenton said.

Study co-author Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research in Germany, compared it to someone lighting a fuse on a bomb, “and then the fuse will burn out to the Big Bang, and the Big Bang may be further along the line.”

While the ice sheets with a few meters or yards of potential sea rise could reshape the coastline over the centuries, Rockstrom told him that the loss of coral reefs is his main concern because of the “immediate impact on human livelihoods.” Hundreds of millions of people, especially poorer residents of tropical regions, depend on fisheries associated with the coral reefs, McKay said.

By just a few tenths of a degree, new tipping points become more possible and even more likely — including a slowing of northern polar ocean circulation that could lead to dramatic weather changes, especially in Europe; loss of certain areas of Arctic sea ice; glaciers collapsing worldwide; and total failure of the Amazon rainforest.

Some of these tipping points, such as the permafrost thaw, are contributing to and accelerating existing warming, but don’t think “game is over” when temperatures warm 1.5 degrees, which is quite likely, McKay said.

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“Even if we get to some of those tipping points, it’s still going to have significant impacts that we want to avoid, but it’s not causing some kind of runaway climate change process,” McKay said. “That is not the case at 1.5 degrees. And that means how much further warming occurs after 1.5 is still largely within our power to effect.”

That’s a crucial point: These are tipping points for individual regional disasters, not for the planet as a whole, so it’s bad, but not the end of the world, said climate scientist Zeke Hausfather of tech company Stripe and Berkeley Earth, who was not part of it. of the study. He said it was important, nuanced research that quantified tipping points better than before.

“Have we really thought about what happens when you mess with our global and ecological systems to that extent?” said Katharine Mach, a climate scientist at the University of Miami, who was not part of the study. She said it has ripples and waterfalls that are troublesome. “This is a major cause for concern in a changing climate.”

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