The Atlantic Ocean current that drives the Gulf Stream is at its weakest for more than 1,000 years – and human-induced climate change is to blame.
Known formally as the Atlantic Meridional Overturning Circulation (AMOC), it is the driving force which brings warm water from the Gulf of Mexico up to the UK and is responsible for mild winters in Western Europe.
Scientists determined that in 2015 it to had slowed by at least 15 percent since 1950, but the latest work paints a picture of how it will develop long term.
Experts warn that by 2100 the AMOC could weaken by as much as 45 per cent, bringing humanity dangerously close to a ‘tipping point’, resulting in devastating weather conditions across the world.
Western Europe would face colder winters, while droughts, storms and heatwaves will become more common. Sea levels would rise along the eastern US coast, with potentially disastrous consequences.
The Atlantic Meridional Overturning Circulation (AMOC) is the driving force which brings warm water from the Gulf of Mexico up to the UK. It is a complex system which is responsible for mild winters in Western Europe and it also influences the level of rainfall
The AMOC was key to the plot of the 2004 film ‘The Day After Tomorrow,’ which depicted the current coming to an abrupt stop and triggering catastrophic storms worldwide.
Although the movie is deemed science fiction, the study by scientists from the Potsdam Institute, Ireland’s Maynooth University and University College London suggests it could become a reality if greenhouse emissions are not curbed.
Study author Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research PIK said: ‘The Gulf Stream System works like a giant conveyor belt, carrying warm surface water from the equator up north, and sending cold, low-salinity deep water back down south.
‘It moves nearly 20 million cubic metres of water per second, almost a hundred times the Amazon flow.
Professor Rahmstorf added: ‘If we continue to drive global warming, the Gulf Stream System will weaken further – by 34 to 45 percent by 2100 according to the latest generation of climate models.
‘This could bring us dangerously close to the tipping point at which the flow becomes unstable.’
His colleague Levke Caesar explained: ‘The northward surface flow of the AMOC leads to a deflection of water masses to the right, away from the US east coast.
‘This is due to Earth’s rotation that diverts moving objects such as currents to the right in the northern hemisphere and to the left in the southern hemisphere.
‘As the current slows down, this effect weakens and more water can pile up at the US east coast, leading to an enhanced sea level rise.’
Direct data from the AMOC is hard to obtain so researchers collected information from a variety of proxy sources dating back around 1,600 years.
It backs up previous findings from the same team which found in 2018 that the ocean current has slowed by 15 per cent since the mid-20th century.
‘In 20 to 30 years it is likely to weaken further, and that will inevitably influence our weather, so we would see an increase in storms and heatwaves in Europe, and sea level rises on the east coast of the US,’ Professor Rahmstorf said.
The new study puts this figure into stark perspective by comparing its meandering pace with that of the last millennium and a half.
Until the 1800s, it was relatively stable but the current declined after the so-called ‘Little Ice Age’ ended in 1850.
Temperatures dropped low enough that the River Thames completely froze over and records show Londoners crossing the waterway on foot.
The last total shutdown of the AMOC is believed to have occurred at the end of the last proper Ice Age around 12,000 years ago, where temperatures in western Europe plummeted by up to 10°C.
Experts warn that by the end of the century it could be so weak it reaches a tipping point which would result in devastating weather conditions across the world
The AMOC was the plot of the 2004 film ‘The Day After Tomorrow,’ which depicted the current coming to an abrupt stop and triggered catastrophic storms worldwide.Pictured Big Ben engulfed in snow
This was likely not due to human impact as the Industrial Revolution had yet to reach full tilt.
But by the 1950s the AMOC had slowed severely as huge amounts of pollution disrupted its formation.
Increased rainfall and enhanced melting of the Greenland Ice Sheet caused by global warming add fresh water to the ocean which reduces the salinity and density of the water.
This subsequently prevents the warm water which has travelled north from sinking as it cools and this breaks the convection cycle, ultimately weakening the flow of the AMOC.
What would the world look like if the Gulf stream collapsed?
If the AMOC was to collapse, far less heat would reach western Europe and the region would be plunged into very severe winters, the kind of scenario depicted in an extreme fashion in the movie The Day After Tomorrow.
Until the 1800s, it was relatively stable but the current declined after the so-called ‘Little Ice Age’ ended in 1850.
Temperatures dropped low enough that the River Thames completely froze over and records show Londoners crossing the waterway on foot.
The last shutdown was probably at the end of the last Ice Age, 12,000 years ago, and it prompted a temperature drop of 5°C to 10°C in western Europe.
In the event of another collapse, not only would European winters become much colder but summer droughts, storms and heatwaves would likely become more common.
Sea levels could rise up to nearly 20 inches around the North Atlantic Basin, which surrounds the eastern US coast.
This would eventually push people living along the coast further inland to escape flooding. A widespread collapse of deep-sea eco-systems would occur.
In the US, Florida would be particularly badly affected as the flow of water northwards would be halted, seeing it collect on the state’s shoreline.
A study published last year looked at how the cessation of the AMOC may impact the UK specifically.
The Little Ice Age, a centuries-long cold period that lasted until about 1850. Experts believe that as the North Atlantic began to warm near the end of the Little Ice Age, freshwater disrupted the system. Pictured is Thames Frost Fair, 1683–84, by Thomas Wyke
University of Exeter researchers made a computer model and found that by 2080 the weather would be 3.4°C colder than it was last year.
Rainfall during the growing season is expected to drop by 123mm, they added.
This, Ars Technica reports, is enough to reduce the UK’s arable land from 32 percent to just seven percent, greatly affecting food production.
The effects would be felt not in Europe and the United States, with forecasts also projecting that the collapse of the AMOC would also increase drought in the Sahel in Africa.
Andrew Meijers, Deputy Science Leader of Polar Oceans at British Antarctic Survey, who was not involved in the study, said: ‘This work provides new long term context and reveals that prior to the era of human induced climate change the Atlantic overturning circulation was relatively stable and stronger than it is now.
‘This indicates that the slowdown is likely not a natural change, but the result of human influence.
‘The AMOC has a profound influence on global climate, and particularly in North America and Europe, so this evidence of an ongoing weakening of the circulation is critical new evidence for the interpretation of future projections of regional and global climate.
‘Additionally, the AMOC is frequently modelled as having a tipping point below some circulation strength, a point at which the relatively stable overturning circulation becomes unstable or even collapses.
‘The ongoing weakening of the overturning means we risk finding that point, which would have profound and likely irreversible impacts on climate.’
The study was published in Nature Geoscience.
