A key system of ocean currents may already be on the verge of breaking up, with alarming consequences for sea-level rise and climate, according to a new report. This will cause temperatures to drop dramatically in some regions and temperatures to rise in others.
The study, published in the journal Science Advances, states that using extremely complex and expensive computer systems, scientists have found a new way to detect an early warning signal of the collapse of these currents. And as the planet warms, there are already signs that it is moving in that direction.
The Atlantic Meridional Overturning Circulation (AMOC), of which the Gulf Stream is a part, works as a giant global conveyor belt that carries warm water from the tropics to the far North Atlantic, where it cools, becomes saltier and sinks deep into the ocean, where it spread south.
Currents carry heat and nutrients to different parts of the globe and play an important role in maintaining a relatively mild climate in large parts of the Northern Hemisphere.
For decades, scientists have been raising the alarm about the stability of the circulation as climate change warms the ocean and melts ice, upsetting the balance between heat and salt that determines the strength of currents.
While many scientists believe that AMOC will slow as a result of climate change and may even stop, there remains enormous uncertainty as to when and how quickly this might happen. AMOK has been observed continuously only since 2004.
Scientists know that from building a picture of the past using ice cores and ocean sediments, the AMOC stopped more than 12,000 years ago after the glaciers rapidly melted.
Now they are trying to find out if it can happen again.
The new research is "an important breakthrough," says René van Westen, a marine and atmospheric researcher at Utrecht University in the Netherlands and a co-author of the study.
Scientists used a supercomputer to run complex climate models for three months, simulating a gradual increase in the amount of freshwater in the AMOC - representing melting ice, as well as rain and river runoff, which can dilute ocean salinity and weaken currents .
With the slow increase in the amount of fresh water in the model, a gradual weakening of AMOC is observed until its sudden collapse. This is the first time the collapse has been detected using these sophisticated models, which is "bad news for the climate system and humanity," the report said.
However, the study did not specify a timeline for a possible collapse. More research is needed, Van Westen told CNN, including models that also mimic the effects of climate change, such as rising pollution levels on the planet, which was not done in this study.
"But at least we can say that we are moving towards the tipping point in climate change," added the researcher.
The consequences of the collapse of AMOK could be catastrophic. According to the study, temperatures in some parts of Europe could drop by up to 30°C in a century, leading to a completely different climate in just a decade or two.
"No realistic adaptation measures can cope with such rapid temperature changes," the study authors wrote.
On the other hand, countries in the Southern Hemisphere may experience increased warming, and in the Amazon, the wet and dry seasons may reverse, leading to severe ecosystem disruptions.
The collapse of the AMOK could also lead to a sea level rise of about 1 meter, says van Westen.
Stefan Ramstorf, a physical oceanographer at the University of Potsdam in Germany who was not involved in the study, said it was a "major advance in the science of the stability of the AMOC."
"It confirms that the AMOC has a tipping point beyond which it breaks down if the North Atlantic becomes depleted of freshwater," Ramstorff said.
According to him, previous studies that found the AMOC critical point used much simpler models, giving some scientists hope that it might not be found in more complex models.
This study dashes hopes, the oceanographer believes.
Joel Hirschi, deputy head of marine systems modeling at the UK's National Oceanographic Centre, said the study was the first to use complex climate models to show that AMOC could flip from 'on' to 'on'. off" in response to relatively small amounts of freshwater entering the ocean.
The new study adds to a growing body of evidence that AMOC may be approaching a tipping point — and that it may even be close.
A 2021 study found that the AMOK was weaker than at any other time in the past 1,000 years. And in a particularly alarming and somewhat controversial report published in July last year, it was concluded that AMOK may be on the verge of collapse possibly as early as 2025. /BGNES
