We’re on track towards a “cliff-like” tipping point where Atlantic Ocean currents abruptly shut down, according to a study published Friday in Science Advances. Once this tipping point is reached, it will have a massive impact on the global climate, including potentially plunging large parts of Europe into a deep freeze and significantly altering the Amazon rainforest’s ecosystem.
The Atlantic meridional overturning circulation (AMOC) acts like an escalator, bringing warm, salty waters northward and upward to the top layers of the Atlantic Ocean, while forcing colder water south into deeper water. Through this process, AMOC redistributes heat around the planet to stabilize climates from Europe to the equator.
Scientists have long been trying to predict how AMOC might morph as a result of human-driven climate change, particularly as melting sea ice sheets make the ocean less salty, messing with the delicate balance between the denser saltwater and less-dense freshwater. The IPCC estimated the escalator might shut down before the end of the century and a 2023 study said it could happen even sooner.
Yet, these estimates were based on a single measure (often sea surface temperature) and some researchers thought once you factor in all the complexities of a climate system, the scenario might disappear. This latest paper, which is based on the most advanced computer modeling so far, disputes this theory.
“This is bad news for the climate system and humanity,” the authors write in their study, adding that their predictions match up with ancient climate evidence that the AMOC has gone through periods of flux, with devastating consequences.
Researchers created a computer model using a global climate model called The Community Earth System Model, which itself is made up of seven sub-models representing the atmosphere, sea and land ice, land, rivers, oceans, and waves. It divides the globe up into much smaller cubes than other models, making the estimates more precise. It also simulated fresh water from sea ice melt flooding the ocean gradually, instead of all at once like other models have done.
The authors say that previous models have overestimated just how stable the AMOC is. Their modeling tells a Day After Tomorrow story (coincidentally, the film was based on an AMOC shutdown). According to the new model, Arctic Sea ice pack in March would extend down further by about 50 degrees latitude, plunging northwestern European temperatures by 5-15 degrees Celsius over several decades. At the same time, temperatures near the equator would rise, swapping around the Amazon’s dry and wet seasons, which could “severely disrupt the ecosystem of the Amazon rainforest.”
However, they can’t estimate how soon the collapse might happen. “We are moving closer to the collapse, but we’re not sure how much closer,” said study lead author Rene van Westen in a press statement.
Nonetheless, van Westen says it might be possible within the 21st century and depends on how much human-made emissions are pushing our climate to its breaking point. “We need to take climate change much more seriously,” the Utrecht University climate scientist told The Guardian.
It’s also made other scientists more concerned about an AMOC collapse. “The new study adds significantly to the rising concern about an AMOC collapse in the not too distant future,” Stefan Rahmstorf, head of Earth Systems Analysis at the Potsdam Institute for Climate Research, in an email to Phys.org. “We will ignore this at our peril.”
According to University of Exeter climate scientist Tim Lenton, who also wasn’t part of the research, it would cause flow-on effects for the Earth’s climate that are “so abrupt and severe that they would be near impossible to adapt to in some locations.”
An AMOC collapse is one of five key tipping points that, once breached—if they haven’t been already—would lead to significant, spiraling, and irreversible changes in our planet’s climate systems. Others include the melting of the Greenland ice sheet, destruction of warm-water coral reefs and boreal permafrost collapse.
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