In the 2004 film ‘The Day After Tomorrow’, humanity is plunged into a nightmarish international storm that sends the planet into a new Ice Age.
And although the blockbuster was consigned to the realms of sci-fi, the science behind the frightening scenario is true.
In a matter of decades, melting glaciers could shut down the Gulf Stream – the system of currents that brings warmth to the Northern Hemisphere, experts say.
Without this additional heat source, average temperatures could drop by several degrees in North America, parts of Asia and Europe, and people would see ‘severe and cascading consequences around the world’.
The scientists warn that an abrupt shutdown of Atlantic Ocean currents is looking more likely than ever, as computer simulations finds a ‘cliff-like’ tipping point looming in the near future.
The study authors, from Utrecht University in the Netherlands, don’t know exactly when the collapse will happen, although a previous study put it as soon as next year.
‘We are moving closer to the collapse, but we’re not sure how much closer,’ said lead author Rene van Westen, a climate scientist and oceanographer at Utrecht University.
‘We are heading towards a tipping point.’
When a global weather calamity like the one in ‘The Day After Tomorrow’ may happen is ‘the million-dollar question’, according to van Westen.
‘We unfortunately can’t answer [that] at the moment,’ he said.
‘It also depends on the rate of climate change we are inducing as humanity.’
The Gulf Stream is part of a much wider system of currents, officially called the Atlantic Meridional Overturning Circulation or AMOC.
Described as ‘the conveyor belt of the ocean’, it transports warm water near the ocean’s surface northwards – from the tropics up to the Northern Hemisphere.
When the warm water reaches the North Atlantic (around Europe and the UK, and the US east coast), it releases the heat and freezes.
As this ice forms, salt is left behind in the ocean water.
Due to the large amount of salt in the water, it becomes denser, sinks down, and is carried southwards in the depths below.
Eventually, the water gets pulled back up towards the surface and warms up in a process called upwelling, completing the cycle.
Scientists think AMOC brings enough warmth to the Northern Hemisphere that without it, large parts of Europe could enter a deep freeze.
Prior studies have already shown that due to climate change, the AMOC is slowing down.
The engine of this conveyor belt is off the coast of Greenland, where, as more ice melts from climate change, more freshwater flows into the North Atlantic and slows everything down.
The new study forecasts that an abrupt shutdown of the AMOC could happen in the next few decades, rather than the next few centuries as previously thought.
The researchers designed a computer modelling simulation in which they were able to measure a sudden weakening of the ocean circulation.
The simulation introduced freshwater into the Atlantic Ocean, and as a result, the circulation strength gradually decreased until it reached a critical ‘tipping point’ and collapsed.
According to the results, the European climate will cool by about 1.8°F (1°C) per decade, and some regions will even experience over 5.4°F (3°C) cooling per decade – much faster than today’s global warming of about 0.36 F (0.2 C) per decade.
Aside from plunging countries into a deep freeze, this would extend Arctic ice further south, turn up the heat even more in the Southern Hemisphere, change global rainfall patterns and disrupt the Amazon rainforest.
Other scientists say it would be a catastrophe that could cause worldwide food and water shortages.
‘We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years,’ the authors said.
‘The heat transport toward the north is strongly reduced, leading to abrupt climate shifts.’
The one thing they couldn’t identify is when exactly this tipping point will be reached, although it is at least decades away if not longer.
‘The research makes a convincing case that the AMOC is approaching a tipping point based on a robust, physically-based early warning indicator,’ said Tim Lenton, chair in climate change at University of Exeter, who was not involved with the study.
‘What it cannot (and does not) say is how close the tipping point, because as it shows that there is insufficient data to make a statistically reliable estimate of that.’
The study has been published in the journal Science Advances.
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
