In 2004, The Day After Tomorrow might have seemed like nothing more than another far-fetched climate disaster movie.
But scientists warn that this movie could soon become reality. A new study shows that climate change could plunge Europe into a deep freeze.
Researchers at University College London have discovered that the Gulf Stream, a vital current of warm water, could be particularly sensitive to changes in the climate.
Their research suggests that global warming could cause the Gulf Stream to collapse, reducing temperatures in Europe by up to 15°C (27°F).
Lead researcher Dr Jack Wharton said: “If winds are weaker in future, as a recent study using climate models shows, it could mean a weaker Gulf Stream and a cooler Europe.”
In 2004, The Day After Tomorrow might have seemed like just another far-fetched climate disaster movie. But now, scientists are warning that this movie could soon become reality.
The Gulf Stream is a warm water current that flows along the east coast of North America and across the Atlantic to Europe.
As it arrives, it releases thermal energy into the atmosphere, keeping Europa at a higher temperature than it might otherwise be.
Some research has already pointed to a weakening of the patterns of ocean currents that determine our planet’s climate.
But to understand how a big change in climate conditions might affect the Gulf Stream in the future, researchers had to look far back in time.
About 20,000 years ago, the planet was immersed in the last Ice Age, which covered much of the northern hemisphere with a thick layer of ice.
However, researchers now believe that Europa may have remained warm despite the surrounding climate thanks to a particularly strong Gulf Stream.
The Gulf Stream is a strong current that carries warm water from the tropics to the coast of North America, across the Atlantic, and toward Europe.
Researchers collected sediment samples from locations along the coasts of North Carolina and Florida to look for the presence of ancient microorganisms called foraminifera.
Co-author Professor David Thornalley told MailOnline: “We used fossils of foraminifera that lived during the last Ice Age because the chemistry of their shells records the density of the water they lived in when they were alive.”
Because Gulf Stream water is very warm, it is less dense than subpolar water, so the researchers were able to use the density recorded by the shells to determine where the Gulf Stream would have flowed.
Because this faster current can carry larger pieces of material, the researchers also looked at the different grain sizes in the sediment to determine its speed.
Using their measurements and some ocean physics, the researchers calculated that the Gulf Stream was twice as deep and twice as fast as it is today.
Dr Wharton says: ‘We found that during the last ice age, the Gulf Stream was much stronger because of stronger winds in the subtropical North Atlantic.
‘As a result, the Gulf Stream continued to transport a lot of heat northward, even though the rest of the planet was much colder.’
Scientists used sediment samples taken from North Carolina and Florida (pictured) to find out how strong the Gulf Stream would have been during the last Ice Age. This revealed that global currents are very sensitive to climate change.
If temperatures continue to rise, there could be devastating effects here on Earth, including a dramatic loss of marine life, an ice-free Arctic and more frequent “extreme” weather conditions.
These findings have worrying implications for our future, as they suggest that the strength of the Gulf Stream depends on climatic factors.
Professor Thornally told MailOnline: ‘The ocean moves huge amounts of heat around the world, equivalent to the energy from millions of power stations.
“Therefore, changing the strength of ocean currents can alter the amount of heat distributed over each location. This alters our climate and, on shorter timescales, our weather.”
The Gulf Stream itself is just one part of the Atlantic Meridional Circulation (AMC), a vast network of currents that pump warm water around the world.
Previous research (pictured) suggests that the collapse of a large ocean current system called the AMOC could cause temperatures to decline by more than 5.4°F (3°C) every 10 years.
Although often described as a conveyor belt, Professor Thornally says it is better to think of the AMOC as “a series of interconnected loops”.
He added: ‘There is the subtropical circuit, of which the Gulf Stream is a part, and a subpolar circuit, which transports heat northwards, towards the Arctic.
‘Our findings show that during the last ice age, the subtropical circuit was stronger than today, while the subpolar circuit is thought to have been weaker.’
One of the biggest concerns is that global warming will disrupt the engine that drives that subtropical circuit.
As ocean water meets the ice around Greenland in the subpolar North Atlantic, it cools rapidly and becomes extremely dense and salty.
This causes the water to sink downward, drawing warm water behind it and creating a wide circulation pattern.
But as fresh water from the Greenland ice sheet melts, it dilutes these cold, salty waters and makes them less dense.
Just like in the Hollywood blockbuster The Day After Tomorrow (pictured), the collapse of the Gulf Stream could lead to rising sea levels and a deep freeze.
Some studies suggest that this could slow the rotation of the subtropical circuit and weaken the Gulf Stream.
The authors of this article also point out that recent studies indicate that climate change is already weakening the strong North Atlantic winds that help drive the Gulf Stream.
Professor Mark Maslin, co-author of the study, said: ‘The extent to which ocean currents are responsible for transferring heat around the planet and shaping our climate is not always recognised.
‘Paradoxically, a warming climate could cool much of Europe by altering the AMOC.’
The cost of sea level rise will be deducted from each country’s gross domestic product (GDP). This map shows the most affected countries (with the largest decrease in GDP due to the cost of sea level rise) in red and orange, and the least affected in green.
Although researchers say they cannot be sure of the impact this will have, in the unlikely event of a complete collapse of the Gulf Stream, temperatures could fall by 10-15°C (18-27°F) in Europe.
Researchers say current climate models show a weakening of the Gulf Stream that is “wreaking havoc” on continental agriculture and weather patterns.
And, just like in the movie The Day After Tomorrow, researchers point out that this could also lead to rising sea levels in North America.
Professor Thornally adds: ‘Changes in the AMOC will also lead to sea level changes around the North Atlantic, with significant rises (tens of centimetres) along the east coast of North America.
‘However, even a more modest weakening of the AMOC will still alter where heat travels, disrupting our normal weather patterns and thought to lead to more extreme weather events, including floods, heat waves and droughts.’
This document has been published in Nature.