Warming oceans could lead to the mass die-off of tropical coral reefs
Helmut Corneli / Alamy
The climate has warmed so much that we are already at risk of triggering five global “tipping points” that would have catastrophic effects worldwide and couldn’t be reversed easily if at all, according to a major report. As the world goes past 1.5°C of warming, it will be increasingly likely that we will cross these tipping points, and there will be a growing risk of this resulting in others as well.
“Triggering one tipping point could trigger another in a kind of dangerous domino effect,” says Tim Lenton at the University of Exeter in the UK, the report’s lead author. “But also these tipping points in the Earth system could, in turn, trigger damaging tipping points in societies, things like food security crises, mass displacement and conflicts. Stopping these threats is possible, but it’s going to require urgent global action.”
A tipping point is where a small alteration in a system can cause abrupt changes that are hard to reverse or are irreversible, because of amplifying feedback processes. Lenton says this is like leaning back on a chair: when it is near the balance point, just a small nudge can make the chair fall over.
The report, put together by more than 200 researchers worldwide, brings together all the existing studies on tipping points and also includes research that is about to be published.
According to the report, the five major tipping points we are near to crossing are: the loss of the Greenland ice sheet, the demise of the West Antarctic ice sheet, the die-off of tropical coral reefs, the abrupt thaw of large areas of Arctic permafrost and the slowing of an ocean current known as the North Atlantic subpolar gyre.
The subpolar gyre is a circular current south of Greenland where salty water cools and sinks. It is linked to the Atlantic meridional overturning circulation (AMOC), but there is growing evidence that the current could slow or stop separately from and sooner than the AMOC, says David Armstrong McKay, also at the University of Exeter.
“[The slowing of the subpolar gyre] could happen within about 10 years,” says McKay. “It would have pretty major impacts across both sides of the Atlantic. It would cause regional cooling and affect agriculture in Europe and North America, and change the patterns of extreme weather events.”
“For some tipping points, we have a very short window for preventive action open right now which might close as soon as the 2030s,” says Manjana Milkoreit at the University of Oslo in Norway, who also worked on the report.
“We think that the prevention of Earth system tipping points should be the core objective of governance efforts because of the scale and severity of the threats that they represent, their cascading potential and the irreversibility of many tipping processes on relevant human timescales,” she says.
Other tipping points include the die-off of seagrass meadows and mangrove forests, and the collapse of fisheries.
There are still huge uncertainties, the report acknowledges. In many cases, it still isn’t clear which systems have tipping points, how close we are to crossing them and what the impacts would be if we did.
Limiting further global warming by getting greenhouse gas emissions down to zero as fast as possible is the main thing that can be done to reduce the risk of triggering tipping points, but in some cases, other measures can help as well, says Milkoreit. For instance, preventing deforestation in the Amazon would reduce the risk of the rainforest dying off and being replaced by grasslands as the region gets hotter and dryer.
The report also calls for more to be done to help communities prepare for the impacts of some tipping points, such as sea level rise.
“Even with a profound acceleration of action, some Earth system tipping points may be unavoidable,” says Lenton. “But still there are things we can do to mitigate the risk they pose by reducing the vulnerability of people to the impacts coming from them.”
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