'Completely Unrealistic' AMOC Collapse
Part One: Could our main ocean current collapse?
Launching a new series of translated articles from the main Norwegian newspapers.
Ocean currents in the Atlantic, such as the Gulf Stream, carry warm water along the Norwegian coast and contribute to ice-free harbours and archipelagos in winter. Here from Lofoten.
Could our main ocean current collapse?
It may suddenly get colder and living conditions for people in the northern regions may be put at risk. The warning comes from 40 climate scientists.
Stine Barstad | stine.barstad@aftenposten.no
Warmer, wetter, wilder. This is how we are used to hearing that global warming will change the climate in Norway. But on Tuesday this week, 40 climate scientists sent a letter to the Nordic Council of Ministers in which they warn that it could suddenly get colder. What is the background for the concern? And how big is the risk really? Here are seven questions and answers that might ease the confusion.
What is AMOC?
This is the name of a large system of ocean currents in the Atlantic Ocean. In English: Atlantic meridional overturning circulation (AMOC), in Norwegian called the circulation in the Atlantic Ocean.
The system sends warm water to the North Atlantic and gives Europe a mild climate.
The Gulf Stream, which is very decisive for the climate in Norway, is part of this system. Without the Gulf Stream, the climate in Norway would be 10–15 degrees colder.
How does this current work?
The Gulf Stream brings heat from the Gulf of Mexico, up through the North Atlantic and into the Norwegian Sea. On its way north, the water cools down. The colder water sinks to the depths and is transported back into the tropics again.
The current system is driven, among other things, by differences in temperature, salinity and wind.
Scientists disagree about what is its most important engine.
Why do scientists fear that the AMOC may run amok?
There is broad agreement that this ocean current will weaken with global warming. Higher temperatures will cause less cold, heavy salt water to be transported southward into the depths. But some researchers also fear that the melting of the Greenland ice sheet will cause the sea to be supplied with so much cold fresh water that the circulation will weaken greatly or collapse.
In the letter, the researchers refer to several new studies which estimate that such a collapse could occur within the next few decades.
What will happen in the event of a collapse?
If the AMOC slows down sharply or collapses, it will have major consequences for the climate and weather patterns across the globe.
Especially for the Nordic countries, the effects will be catastrophic, the researchers warn.
They point out that a large area in the North Atlantic will become significantly colder. At the same time, the surrounding areas become warmer.
Ulysses Ninnemann at the Bjerkness Center in Bergen is one of five Norwegian climate scientists who have signed the petition. He says the temperature in Norway may drop 4-5 degrees within a few decades. The parts of the country that will get a lot of snow and rain will also change.
One of the studies the researchers refer to, estimates that the temperature in Bergen will drop 3.5 degrees every decade and could be up to 30 degrees colder in winter. Meantime, smaller changes in currents could mean Norway becomes a little less warm than it would otherwise be with climate change, writes the Meteorological Institute.
The researchers emphasise that the effects on weather patterns are uncertain and must be studied further. But large and sudden changes may threaten the viability of agriculture in North-West Europe, they write.
How big a risk is there for this?
Here, the scientists strongly disagree.
The UN climate panel says there is a medium probability that the ocean current will not collapse abruptly before 2100. But the researchers say several recent studies conclude that the risk is greatly underestimated. Among other things, they refer to a study done by Danish researchers, who calculate that the AMOC will collapse around 2050. A study by Dutch researchers does not estimate a time, but says it is moving in that direction.
Both studies are highly controversial.
Lars H. Smedsrud and Tor Eldevik at the Bjerknes Centre have previously said that the studies are based on completely unrealistic assumptions.
Why do the scientists accuse each other of crying "wolf"?
In the latest studies, the researchers run simulations in which they provoke a collapse in the AMOC by dumping large amounts of fresh water over a large area of the Atlantic Ocean over a long period of time.
This means that large parts of the sea become brackish water.
This is meant to correspond to a catastrophic melting of the Greenland ice sheet.
The problem is that this would never happen that way in reality. Then the fresh water would have been carried with ocean currents and mixed in a different way, explains Eldevik.
— And if Greenland melts down, we will have other and bigger problems: Then the sea level would rise seven meters globally, he says.
His colleague and
director at the Bjerknes Center, Kikki Fleische Kleiven, is among the researchers who have signed the warning.
— I personally am on the more moderate side, and think the word "collapse" is polarising, she writes in an e-mail to Aftenposten.
She says there is agreement that the system will change in a warmer world, and believes it is important to emphasise that there is "some disagreement" about how much. She says the problems with predicting the future of the important ocean currents are in themselves a reason to sound the alarm.
So: How worried should we be about a suddenly colder climate here in the north?
— It is a possibility that one cannot completely dismiss, but it is extremely unlikely. And the Gulf Stream is not going to stop as long as we are on a rotating globe and the wind blows, says Eldevik.
— I am more worried about climate change than ever, but not about this. It is also statistically possible that I will be hit by a meteorite, but I don't spend much time worrying about it, says Eldevik.
He adds that a recent study shows that the strength of the Gulf Stream has been stable for the past 40 years.
Kleiven says that few scientists believe that the AMOC will stop completely.
- But even a change in parts of this system, which is not ruled out, is something we have not seen in the history of our civilisation. I think it's difficult for most people to take in what that might mean, she says.
The Gulf Stream (fact box)
-10°C
The Gulf Stream is part of the AMOC — a large system of ocean currents in the Atlantic Ocean. Without the Gulf Stream, the climate in Norway would be 10–15 degrees colder.
2100
The UN climate panel says there is a medium probability that the [AMOC] ocean current will not collapse before 2100. A Danish study calculates that the AMOC will collapse around 2050. A Dutch study says it is going in that direction. Both studies are highly controversial.