Can the UK actually be cooler than global warming?

Of all possible climate future, there is a scenario in which the United Kingdom and Northwestern Europe break through the trend of global warming and instead face the fall of temperatures and freezing winter.

This is not the most likely outcome, but numerous scientists fear that the chance will happen and that the consequences would be so large that it deserves proper consideration.

They are worried that the ocean currents that bring warm water from the tropics to the northern Atlantic can weaken – or even demolish – in response to climate change.

Huge insecurity remains about when – or even – a collapse could happen. Well, how likely is it and what would it mean?

The Atlantic current system, called the Atlantic Meridian Rolling Circulation (AMOC), is the key reason why the UK is warmer than Moscow, although a similar distance from the equator.

Forming a vital part of our climatic system, this transport belt distributes energy around the planet, bringing hot, salty water from the tropical Atlantic to the cooler regions south of Greenland and Iceland, and also of the Nordic seas.

The heat from the ocean is transmitted into the air above it, helping that temperatures are milder than they would otherwise be.

As this salty water cools, it becomes denser and sinks, before returning to the southern hemisphere as the deep current of the ocean. This water eventually retreats to the surface and the circulation continues.

But Amoc seems to be weaker.

We do not know for sure, because they have been direct and continuous measurements of the AMOC power only since 2004. This is not long enough to be able to recognize a certain change.

But indirect evidence suggests that it could slow down by about 15% in the last few centuries, although not all scientists agree.

One indicator is sediments at the bottom of the ocean. Larger grains indicate a stronger current. By measuring the size of cereals and calculating their age, scientists can estimate how much amoc has slowed over time.

Another proof is the so -called ‘cold stain’ or ‘heating hole’ in the northern Atlantic. This describes the region that she seems to have cooled in recent decades, unlike the vast majority of the world.

Decorating Amoc – which means that less warmer water would be translated into this region – it is considered a possible culprit.

This is “a very clear signature and a trace of the classic slowdown of Amoc,” says Matthew England, a professor of Oceanography at the University of Novi South Wales.

The UN -IPCCUME SPRIGHMS (IPCC) is expecting that Amoc will weaken this century. But the main concern is that Amoc could suddenly be “excluded”, as it seems to have happened repeatedly in the Earth’s past.

Today, global warming seems to make water in the northern Atlantic less salty, due to additional fresh water from ice ice than melted Greenland and more rain.

As the fresh water does not sink so easily, it is expected that this will slow down the circulation and thus bring less salty water from the tropics to the north.

In addition to the “turning point”, this loop could bring Amoc to an angry collapse.

“We really want to avoid a turning point because we can’t do anything at the time,” warns David Thornalley, a professor of Ocean and climate science at University College London.

No one really knows how close it is.

IPCC said in 2021 that he had “medium confidence” that Amoc would not abruptly collapse this century, although he expected to weaken.

But some recent studies have pointed to the growing possibility for Amoc to pass the turning point in the coming decades, beyond which the full collapse would be inevitable.

Each study comes with different warnings and insecurities, and different climate models can give different results for the system complex as Amoc.

“We do not believe that the idea of ​​the AMOC collapse has changed significantly because of these new results,” warns Dr. Laura Jackson, Oceanographer in Met’s Office.

But many scientists are becoming more and more concerned. Professor Thornalley claims that, regardless of the imperfections of individual studies, together they “lead to the conclusion that we may need to worry.”

After new evidence, more than 40 leading scientists on the ocean and climate signed An open letter Last October, calling for wider risk recognition of “greatly underestimated”.

This does not mean that the signatories believe that Amoc of this century will pass the turning point. But they warn that now the possibility is sufficient to justify proper consideration.

“I would say that you are looking at the risk of reaching a turning point in the coming decades that could be at a level of 10 or 20%, even if we are held at 2C warming [above temperatures of the late 19th Century, before humans started significantly warming the climate]”warns Tim Lenton, professor of the science of the earthly system at the University of Exeter.

Given the size of the consequences of the AMOC collapse, these likelihood “are not trivial,” he adds.

Even the most likely scenario – where Amoc still weakens this century – could have serious effects.

“If AMOC gradually weakens in the next century, you will get global warming, but less warming over Europe,” says Dr. Jackson.

This would still mean that in the UK, it became hot summers with climate change, but the weaker Amoc could also encourage more winter storms as regional temperature samples change.

In the meantime, the collapse would be completely “like a war situation […] Something almost unimaginable, “says Prof. Lenton.

Although it could take a century or more blows, temperatures in northern Europe could drop in several degrees for decades.

In the UK, it could “become terrible, terribly cold … like life in northern Norway,” warns prof. Thornalley.

“Our infrastructure is not set for that.”

There could also be global consequences, such as moving to tropical rain belts.

“It’s a big story,” Profa Lenton warns.

“If you lost the monsoon or seriously disturbed it, you would have humanitarian disasters, simple words, in West Africa [and] probably in India. “

How we prepare for this alternative future is challenges for governments.

Prof. Lenton draws parallels with Pandemi -19 pandemia preparations – another big event that scientists have warned, but they couldn’t know when it could happen.

But Warned the recent report The UK has a “glittering blind place for national safety for climate threats”, such as those represented by Amoc collapse. IN The government acknowledged last year that “did not evaluate the effect of any [Amoc] slowing down or demolishing “at economic planning.

Scientists are clear that the fundamental way to reduce these risks is to reduce greenhouse gas emissions causing climate change.

“We play a slightly Russian roulette game,” warns Prof. England.

“The more we agree with the atmosphere with greenhouse gases, the more we warm up the system, the more a chance of slowing and collapsing Amoc.

“And so I don’t think people need to give up, because so much can be gained by reducing emissions.

“The circumference of change is just so much worse if we do nothing.”

Graphics Erwan Rivault