According to a recent analysis of 150 years of temperature data, the delicate circulation system of the Atlantic Ocean has gotten slower and less resilient, raising the likelihood that this critical component of the climate system may collapse within the next few decades.

Researchers have long regarded the Atlantic Meridional Overturning Circulation, or AMOC, as one of the planet's most susceptible "tipping elements" —meaning it could see a rapid and permanent shift, with significant ramifications for the rest of the world. 

This aquatic circulation system transfers warm, salty water from the tropics to the North Atlantic and then distributes cooler water south along the ocean floor under current conditions. With global temperatures rising,  the consequent flood of cold freshwater has put a hitch in the system – and may completely shut it down.

The study, published in the journal Nature Communications on Tuesday, found that ongoing warming will drive the AMOC beyond its "tipping point" towards the middle of this century. The transition would be as rapid and permanent as turning off a light switch, and may cause severe weather shifts on either side of the Atlantic.

"Humans need a hard foot on the brake"
 
Peter Ditlevsen, a climate physicist at the University of Copenhagen and the study's main author, called the result "really worrying," detailing that humans need "a hard foot on the brake," of greenhouse gas emissions.

Ditlevsen's research contradicts the most recent assessment from the United Nations Intergovernmental Panel on Climate Change, which used various climate models and determined with "medium confidence" that the AMOC will not collapse completely this century.

Other AMOC specialists noted that because the current study does not give new observations of the whole ocean system, but rather extrapolates about the future based on prior data from a narrow portion of the Atlantic, its results should be interpreted with caution.

The finding adds to the mounting evidence that this vital ocean system is in jeopardy. Studies from a network of ocean buoys have suggested that the AMOC has been weakening since 2004, albeit the small time range of that data set makes establishing a pattern difficult. Scientists have also examined several "proxy" markers of the current's intensity, such as microscopic creatures and small seafloor sediments, and discovered that the system is currently in its lowest state in over 1,000 years.

Ditlevsen and his sister Susanne, a statistician at the University of Copenhagen, studied surface temperatures on the sea going back to 1870. They discovered larger variations in temperature in the Atlantic's northernmost areas in recent years that have taken longer to recover to normal. According to the scientists, these are "early warning signals", indicating the AMOC is becoming dangerously unstable, similar to the more erratic wobbles that precede the collapse of a Jenga tower.

Read more: Human-caused climate change causing 'ocean amnesia'
 
Susanne Ditlevsen then created a sophisticated mathematical model to forecast how much more tremor the AMOC system can withstand. According to the findings, the AMOC might collapse at any moment between now and 2095, possibly as early as 2025.
 
The ramifications would be far less severe than in the movie "The Day After Tomorrow," in which an abrupt cutoff of the current triggers a flash freeze throughout the Northern Hemisphere. However, dips in temperatures in northern Europe, increased warmth in the tropics, and heavier storms on North America's East Coast may occur.  

Marilena Oltmanns, an oceanographer at the National Oceanography Center in the United Kingdom, stated that the temperatures in the North Atlantic are "only one part of a highly complex, dynamical system."

In 2022, the oceans absorbed around 10 zettajoules more heat than in 2021, which is comparable to every person on Earth using 40 hairdryers all day, every day.

The warming of the oceans, as well as the effects of extreme weather, will worsen until mankind achieves net zero emissions.

The World Meteorological Organization reported in October 2022 that the concentrations of all the major greenhouse gases - carbon dioxide, methane, and nitrous oxide - in the atmosphere had reached record highs. Prof. Petteri Taalas, chairman of the World Meteorological Organization, stated, "We are moving in the wrong way."