Global warming above 1.5C, the Paris Agreement’s most ambitious goal, could trigger several climate “tipping points” that would set off catastrophic chain reactions, according to a study published Thursday in Science magazine.
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And current temperatures, already rising, threaten to initiate five of those fractures, including those affecting the Antarctic and Greenland ice caps, warn the study’s authors, who believe it’s not too late to act.
“For me, it’s going to change the face of the world – literally, if you look at it from space,” with sea level rise or forest destruction, Tim Lenton, one of the key contributors, told AFP the study’s authors.
In 2008 he signed the first major publication on the subject.
A “tipping point” is “a critical threshold beyond which a system reorganizes, often brutally and/or irreversibly,” according to the UN Panel of Climate Experts (IPCC) definition. These are phenomena that independently and inevitably trigger other cascading consequences.
While initial analyzes estimated their trigger threshold to be in the range of 3 to 5°C warming, advances in observation and climate modeling as well as in the reconstruction of past climate zones have drastically lowered this estimate.
The study, published in Science, is a synthesis of more than 200 scientific papers conducted to better predict the trigger levels of these fracture sites.
The authors identify nine major “tipping points” at the planetary level and seven at the regional level, for a total of 16.
Of these, five could be triggered by current temperatures that have risen by an average of almost 1.2°C since pre-industrial times: the ice caps in Antarctica and Greenland, a sudden thawing of permafrost, the end of a heat transfer phenomenon in the Labrador Sea, and the extinction from coral reefs.
According to the study, if the temperature rises by 1.5°C, four more points will move from the category “possible” to “probable”, five more will then become “possible”.
“Sociological turning point”
For the West Antarctic and Greenland ice caps, exceeding the fracture point scientists estimate would contribute 10 meters of sea level rise over hundreds of years, says Tim Lenton of the British University of Exeter.
If coral reef destruction has already begun, rising temperatures could make that destruction permanent, affecting the 500 million people who depend on it.
In the Labrador Sea, a heat exchange (or convection) phenomenon that brings warm air to Europe could be disrupted, leading to colder winters like the continent experienced during the Little Ice Age.
Accelerated thawing of the permafrost would release huge amounts of greenhouse gases and fundamentally change the landscapes of Russia, Canada and Scandinavia.
At 1.5°C warming, a major ocean current in the Atlantic (the AMOC) would be disrupted and at 2°C this would be the case for the West Africa and Sahel and Amazon monsoons, which could then turn into Savannah.
Those devastating effects depend on the duration of the warming, explains study lead author David Armstrong McKay: When the 1.5°C levels off for 50 or 60 years, the planet will face its worst consequences.
But these “tipping points” will do very little to make warming itself worse, he adds, believing humanity can still limit damage going forward. “It always pays off to reduce our emissions as quickly as possible,” pleads the scientist.
Tim Lenton, one of the world’s leading experts in this field, would like to believe that this concept of rupture as a “sociological tipping point” that inspires action can be applied more positively to the fight against the climate crisis.
“That’s how I manage to get up in the morning,” he explains. “Can we change our lifestyle, transform it? Thinking systemically, with this idea of a predetermined breaking point, gives us a glimmer of hope.”