A system of currents in the Atlantic Ocean that acts like a massive conveyor belt redistributing warm water throughout our planet’s oceans is the weakest it has been in more than 1,000 years – and human-induced climate change is to blame.
Formally known as the Atlantic Meridional Overturning Circulation (AMOC), it powers the Gulf Stream that brings warm water from the Gulf of Mexico to the northeastern US coast.
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 percent, bringing humanity dangerously close to a ‘tipping point’ that would result in devastating weather conditions across the world.
If these predictions become our reality, sea levels will rise along the eastern US coast and Western Europe would experience extreme weather more frequently.
Formally known as the Atlantic Meridional Overturning Circulation (AMOC), it powers the Gulf Stream that brings warm water from the Gulf of Mexico to the northeastern US coast. Experts warn that it is slowing and could increase sea levels along the northeastern US coast
The consequences of the AMOC slowdown could be manifold for people living on both sides of the Atlantic as Levke Caesar explains: ‘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.’
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.
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.
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
Because direct data from the AMOC is hard to obtain, researchers instead collected information from a variety of proxy sources dating back around 1,600 years. The team cites proxies such as surface temperature and marine productivity, and found nine out 11 (pictured) show a clear weakening trend
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 is a scene of New York being flooded
‘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.’
What would the US be like if the Gulf Stream stopped?
A complete shutdown of AMOC would result in a cooling of the entire Northern Hemisphere.
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 weakened AMOC would also decrease the amount of rainfalls in the North Atlantic, which could sparks droughts along the east coast.
Because direct data from the AMOC is hard to obtain, researchers instead collected information from a variety of proxy sources dating back around 1,600 years.
The team cites proxies such as surface temperature and marine productivity, and found nine out 11 show a clear weakening trend.
This works stems from the team’s previous finding in 2018 that found the ocean current has slowed by 15 percent since the mid-20th century.
But Rahmstorf told The Washington Post that the latest evidence ‘makes this conclusion considerably stronger.’
The team notes a recurrent ‘cold blob’ that was first spotted in 2015 in the Atlantic Ocean that is cooling as the rest of the world heats up is caused by shifting ocean currents and low-level cloud.
Researchers believe that this is evidence that not enough warm water is reaching the south of Greenland, where the cold blob sits, due to a weakening AMOC.
And it could be because of runoff from melting glaciers is overpowering the waters.
Separate work from the University of Arizona Department of Geosciences attributed an increase in sea levels from New York to Newfoundland to the AMOC slowing down by 30 percent from 2009 to 2010, as well as unusual wind currents that pushed ocean waters towards the coast.
Dr. Richard Wood, who leads the climate, cryosphere and oceans group at the Met Office, also warns that ea levels could rise up to nearly 20 inches around the North Atlantic Basin, which surrounds the eastern US coast as a result of a slowed AMOC.
Another team of US scientist also say the weakened AMOC explains a reduction in Arctic sea ice loss in all seasons and, in particular, a delay by about 6 years of the emergence of an ice-free Arctic in boreal summer.
AMOC is a natural way of Earth keeping water temperatures balances throughout the oceans, along with keeping weather systems stable.
Areas near the equator are hit with direct sunlight than the colder poles, which results in heat building up in the tropics.
Although a majority of the heat is redistributed by the atmosphere, the Global Ocean Conveyor Belt picks up the rest and moves it throughout the world’s oceans – sending it in all different directions horizontally and vertically.
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
And the engine that drives this is the AMOC, which moves water at 100 times the flow of the Amazon river.
The Gulf Stream carries warm, salty water from the tropics near Florida up to the North Atlantic.
WHY ARE OCEAN CURRENTS SO IMPORTANT?
Ocean currents play a critical role in regulating the planet.
Slower circulation in the North Atlantic can yield profound change on both the North American and European climate but also on the African and Asian summer monsoon rainfall.
This transfer of heat and energy not only has direct influence on climate over Europe and North American but can impact the African and Asian monsoon system through its effect on sea surface temperature, hydrological cycle, atmospheric circulation and variation in the intertropical convergence zone.
Once the band of water hits the area around Greenland, it cools just enough to become more dense and heavier that surrounding waters, and then it sinks.
And if the AMOC slows it could spell disaster for the Northern Hemisphere’s climate.
However, the weakening of the AMOC did not spark overnight.
Until the 1800s, it was relatively stable but the current declined after the so-called ‘Little Ice Age’ ended in 1850.
This was likely not due to human impact as the Industrial Revolution had yet to reach full tilt.
Scientists first observed a weakening in the 1950s, 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 traveled north from sinking as it cools and this breaks the convection cycle ultimately weakening the flow of the AMOC.
Dr 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 modeled 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.