The Atlantic Meridional Overturning Circulation, or AMOC, has become increasingly unstable in recent years – a situation scientists believe is caused by global warming. The major current is responsible for moving warm, surface-level waters northwards from the tropics, and cold water from the ocean floor southwards. Should the AMOC collapse, it could bring extreme colds to parts of Europe and North America.
The findings were published this week in the journal Nature Climate Change.
The study's lead author, Niklas Boers from the Potsdam Institute for Climate Impact Research, said: "The Atlantic Meridional Overturning really is one of our planet's key circulation systems."
Based on computer simulations and data collected from Earth's past, scientists know the current can be disrupted or exhibit "an alternative, substantially weaker mode of operation".
This is particularly alarming as scientists believe the AMOC is presently at its weakest state in more than 1,000 years.
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According to the Met Office, the AMOC works like a large conveyor belt that is driven by differences in temperature and water salinity.
The current, which spans the breadth of the globe, makes sure the oceans are mixed and heat and energy are distributed around the planet.
Annual variations in the current contribute to weather in the UK, and scientists have been tracking these changes since at least 2004.
Should this process be disturbed, the potential fallout could be catastrophic.
Climate models suggest the AMOC will weaken throughout the 21st century as a result of greenhouse gas emissions and climate change.
As global warming causes ocean temperatures to rise, the ocean floor retains its heat.
At the same time, ice melt at the polar caps and increased rainfall are expected to dump large quantities of freshwater into the oceans.
According to the Met Office, this could result in a cooling of temperatures in the UK.
The national forecaster said: "A weaker AMOC will bring less warm water northwards, and this will partly offset the warming effect of the greenhouse gases over western Europe.
"For the gradual weakening that is likely over the 21st Century, the overall effect is still a warming."
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With the AMOC out of whack, not only will freezing temperatures hit the North Atlantic, but sea levels are also expected to rise along the coasts.
The AMOC hasn't reached the tipping point just yet but the evidence is mounting to suggest it is becoming increasingly unstable.
Dr Boers said: "A detailed analysis of these fingerprints in eight independent indices now suggests that the AMOC weakening during the last century is indeed likely to be associated with a loss of stability.
"The findings support the assessment that the AMOC decline is not just a fluctuation or linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse."
As the AMOC current drives warm, salty water northwards - what we know as the Gulf Stream – where it cools and becomes more dense, falling beneath the surface of Greenland.
But this process is being disturbed by climate change – namely rising temperatures and the melting of polar ice is changing the salinity and density of water in the north.
This may prevent the southerly waters from sinking to the bottom of the ocean, throwing the entire system off-kilter.
Dr Boers said: "I wouldn’t have expected that the excessive amounts of freshwater added in the course of the last century would already produce such a response in the overturning circulation.
"We urgently need to reconcile our models with the presented observational evidence to assess how far from or how close to its critical threshold the AMOC really is."