Four major climate tipping points near the trigger

Even if the world somehow manages to limit future warming to the strictest international temperature target, four Earth-changing climate “tipping points” are still likely to be triggered with many more as the planet warms further after that. according to a new study.

An international team of scientists looked at 16 climate tipping points – when a side effect of warming is irreversible, self-perpetuating and significant – and calculated rough temperature thresholds at which they occur. None of these are considered likely at current temperatures, although some are possible. But with just a few tenths more of a degree of warming from now, at 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times, four are moving into the likely range, according to a study in Thursday’s Science journal.

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

“Let’s hope we’re wrong,” said study co-author Tim Lendon, an Earth systems scientist at the University of Exeter in the United Kingdom. “There is a distinct possibility that some of these tipping points are inevitable. And so it’s very important to think a little bit about how we’re going to adapt to the consequences.”

Timing is a key issue for tipping points in two ways: when they trigger and when they cause damage. And in many cases, such as ice sheet collapse, they could be triggered soon, but their effects, while inevitable, take centuries to play out, scientists said. Few, like the loss of coral reefs, cause more damage in just a decade or two.

“It’s a future generation issue,” said study lead author David Armstrong McKay, an Earth systems scientist at the University of Exeter. “That the ice sheets collapsing is kind of on that millennial timeline, but it’s still bequeathing a completely different planet to our descendants.”

The concept of tipping points has been around for more than a decade, but this study goes further by looking at the temperature thresholds for when they might be triggered and what effects they would have on people and the Earth, and over the past 15 years or so, “risk levels have simply keep going up,” Lenton said.

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

“When you start tipping backwards, you have in this case a very simple kind of feedback about the forces of gravity acting to push you backwards all the way to SPLAT,” Lenton said.

Study co-author Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research in Germany, likened it to someone lighting a fuse in a bomb “and then the fuse will burn until the big bang, and the big bang can be below. line.”

While ice sheets with many meters or yards of potential sea rise can reshape the coastline over centuries, Rockstrom told him that the loss of coral reefs is his biggest concern because of the “immediate impacts on human livelihoods”. Hundreds of millions of people, particularly the poorest people in the tropics, depend on fisheries linked to coral reefs, McKay said.

With a few more tenths of a degree new tipping points become stronger and even more likely, including a slowing of the northern polar ocean circulation that can lead to dramatic weather changes especially in Europe, loss of some Arctic sea ice areas, global and absolute glacier collapse failure of the Amazon rainforest.

Some of these thresholds, such as thawing permafrost, add to and accelerate existing warming, but don’t think it’s “game over” if temperatures reach 1.5 degrees of warming, which is highly likely, McKay said. .

“Even if we hit some of these tipping points, it’s still going to have really substantial impacts that we want to avoid, but it doesn’t trigger some kind of unexpected climate change process,” McKay said. “That doesn’t happen at 1.5 degrees. And that means that how much further warming will occur beyond 1.5 is still mostly within our power to realize.”

That’s a critical point that these are tipping points for individual regional disasters and not for the planet as a whole, so it’s bad, but not the end of the world, said climatologist Zeke Hausfather of the tech firm Stripe and Berkeley Earth, who did not was part of the study, but said it was important nuanced research that quantified the tipping points better than before.

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

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