Scientists from the University of California, Riverside, have warned that the Gulf Stream has been weakening for more than 100 years – and could soon collapse altogether.
The Gulf Stream is only a small part of a much wider system of currents, officially called the Atlantic Meridional Overturning Circulation (AMOC).
Described as ‘the conveyor belt of the ocean’, AMOC transports warm, salty water near the ocean’s surface northwards from the tropics up to the northern hemisphere.
This is crucial for keeping Europe, the UK, and the US east coast temperate.
Worryingly, if the AMOC does collapse, it could plunge large parts of Europe into a deep freeze.
In fact, scientists have predicted that parts of the UK could drop to as low as -30°C.
‘This work shows the AMOC has been weakening for more than a century,’ said Professor Wei Liu, an author of the study.
‘That trend is likely to continue if greenhouse gases keep rising.’
The researchers point to a strange patch of cold water south of Greenland and Iceland, about 1,000 miles wide, that really shouldn’t be there.
Unlike the water surrounding it, this ‘stubborn’ patch of cold water has resisted global warming for more than a century, long fueling debate amongst scientists.
Now, the new study, published in the journal Communications Earth & Environment, finally links it to a long-term weakening of the AMOC.
‘People have been asking why this cold spot exists; we found the most likely answer is a weakening AMOC,’ said lead study author Wei Liu.
Lui and a colleague analysed about 100 years of salinity and temperature data, which can be used to understand the strength of the AMOC.
When the AMOC slows down, less heat and salt reach the North Atlantic, leading to cooler, fresher, less salty surface waters.
From these long-term salinity and temperature records, they reconstructed changes in the circulation system and compared those with nearly 100 different climate models.
They found that only the models simulating a weakened AMOC matched the real-world data – indicating that a weakened AMOC was the only possible cause for the blob.
Professor Li described it as a ‘very robust correlation’, adding: ‘If you look at the observations and compare them with all the simulations, only the weakened-AMOC scenario reproduces the cooling in this one region.’
Until now, some climate scientists had thought the random cool patch south of Greenland has been due to atmospheric factors such as aerosol pollution.
But computer models testing this theory have before now failed to recreate the actual, observed cooling – as these experts have done with the now-proven AMOC theory.
The team say the study strengthens future climate forecasts, especially those concerning Europe, where the influence of the AMOC is most pronounced.
While previous studies have offered evidence that the AMOC is weakening, this anomalous blob in the Atlantic offers physical, tangible evidence.
Professor Liu emphasized the complexity of the AMOC’s role in the global climate, but warned what a total collapse of the system could mean.
‘The overall impact on ecosystems and weather patterns, both in the Arctic and globally, could still be severe,’ he said.
Professor David Thornalley, a climate scientist at University College London who was not involved with the study, said temperatures would plummet if the AMOC collapsed.
‘An AMOC collapse could cause more weather extremes, so as well as overall colder-than-average conditions, we also expect that there would be more winter storms caused by stronger westerly winds,’ he previously told MailOnline.
‘Unfortunately people would die due to stronger winter storms and flooding, and many old and young would be vulnerable to the very cold winter temperatures.’
In the UK, the effects could be ‘minor’ compared with elsewhere around the world, Professor Thornalley added.
‘A collapse in AMOC would cause a shift in the tropical rainfall belt which would massively disrupt agriculture and water supplies across huge swathes of the globe,’ he said.
‘Many millions would be affected and suffer from drought, famine and flooding, in countries that are already struggling to deal with these issues. There would be huge numbers of climate refugees, geopolitical tensions would rise.’
Jonathan Bamber, a professor of Earth observation at the University of Bristol, agreed that if the AMOC were to collapse, the climate of northwest Europe would be ‘unrecognisable compared to what it is today’.
‘It would be several degrees cooler so that winters would be more typical of Arctic Canada and precipitation would decrease also,’ he told MailOnline. ‘Very harsh, cold winters would certainly be a threat to life.’
In ‘The Day After Tomorrow’, a collapse of the AMOC takes place over a matter of days and the fictional weather immediately switches to extreme cold.
Thankfully, such a rapid transition will not happen in real life, said Penny Holliday, head of marine physics and ocean circulation at the National Oceanography Centre in Southampton.
‘If the AMOC does reach a tipping point it will happen over several decades at least,’ she told MailOnline.
‘However a slowdown of the AMOC, whether it is fast-acting or takes place over many decades, will lead to the generation of more extreme and violent weather systems that have the potential to cause deaths and major damage.’
Last week, another team of scientists reported temperatures could plunge to -30°C in Scotland if the AMOC collapsed, with Edinburgh spending nearly half of the year with a minimum temperature of below 0°C.
London, meanwhile, would experience cold extremes of -19°C and record over two months’ worth of additional days with sub-zero temperatures compared to the late 19th century.
Is ‘The Day After Tomorrow’ an accurate portrayal of the future?
Paleoclimate records constructed from Greenland ice cores have revealed that AMOC circulation has, indeed, shut down in the past and caused regional climate change, according to the University of Illinois.
It caused the area around Greenland to cool by 44 degrees Fahrenheit.
In the 2004 film ‘The Day After Tomorrow,’ New York City’s temperature dramatically dropped to a point that a deep freeze appeared within a day.
Even a second outside and the movie’s characters would freeze to death.
Scientists say the film plays up the shift, which would take decades to see, but note temperatures would dramatically decrease along the eastern US coast.
Winters would become colder and storms more frequent that would linger longer throughout the year if the AMOC would come to a halt today.
However, scientist say it isn’t the cold temperatures that we should prepare for, it will be the rise in sea levels that will have the largest impact.
The increase would be caused by water piling up along the east coast that would have been pushed away by the northward surface flow.
But with AMOC weakened, or at a stop, experts say sea levels around the North Atlantic Basin could experience a rise up to nearly 20 inches.
This would eventually push people living along the coast from their homes and further inland to escape flooding.
A weakened AMOC would also decrease the amount of rainfalls in the North Atlantic that would cause intense droughts in areas that rarely experience such events.
