Ominous study reveals what will happen if the Gulf Stream collapses

Scientists have revealed exactly what will happen if a critical ocean current collapses.

The Atlantic Meridional Overturning Circulation (AMOC) is a vast system of ocean currents, of which the vital Gulf Stream is just one part.

Studies have previously suggested that its abrupt collapse could plunge northern Europe into a new Ice Age.

However, scientists from the Potsdam Institute for Climate Impact Research now claim that this climate disaster could actually make parts of the world even hotter.

The scientists’ computer simulations revealed that halting this key current will release vast stores of carbon currently trapped deep beneath the ocean.

This would increase the concentration of CO2 in the atmosphere by 47 to 83 parts per million, triggering up to 0.27°C (0.5°F) of additional warming worldwide.

Although this will offset Europe’s cooling, temperatures in the Northern Hemisphere will still plummet, with the Antarctic becoming 7°C (12.6°F) colder.

Meanwhile, this extra carbon will drive extreme warming in the South – raising temperatures in the Arctic by 6°C (10.8°F).

The AMOC functions like a giant ocean conveyor belt, transporting water and heat all around the globe.

The ‘engine’ that powers this conveyor belt is the sinking of cold, salty water in the freezing oceans around Greenland.

As warmer water freezes, it becomes saltier and denser, sinking to the bottom of the ocean and pulling more warm water northwards in its wake.

However, as fresh water from melting glaciers pours into the ocean, the water around the poles is becoming less dense, gradually slowing the AMOC’s steady flow.

Previous studies have warned that AMOC is teetering on the edge of a tipping point, beyond which the entire system will suddenly collapse and grind to a halt.

Without AMOC to redistribute heat around the planet, scientists predict that the Northern Hemisphere will cool while the Southern Hemisphere warms.

However, what scientists have previously not considered is how this might affect the world’s supply of carbon dioxide.

Johan Rockström, director of the Potsdam Institute for Climate Impact Research, says: ‘The ocean has been our greatest ally, absorbing a quarter of human–made CO2 emissions.

‘Our study shows how an AMOC collapse could flip the Southern Ocean from a carbon sink into a carbon source, releasing vast amounts of CO2 and fuelling further global warming.’

Using sophisticated computer simulations, the researchers modelled the AMOC current at various concentrations of atmospheric CO2 before adding fresh water until the system collapsed.

In every simulation, the researchers saw that the collapse of AMOC led to a spike in CO2 concentration and increased global warming.

Co–author Dr Matteo Willeit explained that this is due to ‘enhanced mixing that brings carbon–rich deep waters to the surface.’

That could be good news for people living in the northern hemisphere, since the extra CO2 will mitigate some of the cooling caused by AMOC’s collapse.

But in the southern hemisphere, that will only compound the intense heating that will follow the disaster.

The simulations also revealed that the more CO2 there is in the atmosphere when AMOC fails, the worse the impacts will be.

When atmospheric CO2 concentrations exceeded pre–industrial levels in the simulation, the current’s collapse led to even more CO2 being released.

At 450 parts per million, the combined effects of global warming would increase temperatures in the Antarctic by more than 10°C (18°F).

This could spell disaster for the continents’ already–fragile ice sheets and glaciers, threatening to increase global sea levels.

Studies have predicted that the collapse of Antarctica’s Thwaites Glacier, known as the Doomsday Glacier, could increase sea levels by a staggering 65 centimetres.

Likewise, if AMOC were to collapse while CO2 concentrations are high, it is much more likely that the change would be irreversible.

At concentrations above 350 parts per million, far below today’s concentration of 420 parts per million, AMOC would never recover from its collapse.

Dr Willeit says: ‘Higher CO2 concentrations fundamentally alter the AMOC’s stability, pushing the system into a bistable regime where the AMOC could weaken over hundreds of years before shifting to, and remaining in, a collapsed state.

‘Once shutdown, we see it does not recover in the long run.’