Swedish agency investigates risk of AMOC collapse
A growing number of research studies warn that the ocean circulation system Amoc could be approaching a tipping point already this century. Something that would lead to severe cooling in Sweden, and that has prompted the Swedish Meteorological and Hydrological Institute (SMHI) to begin assessing the risks this could pose to society.
In October 2025, a group of researchers gathered for a workshop in Helsinki. The background was an open letter to the Nordic Council of Ministers, signed by 44 international climate researchers, who expressed their concern that the UN’s climate panel IPCC had greatly underestimated the risk of the Atlantic Meridional Overturning Circulation (Amoc) collapsing.
In their letter, the researchers wrote that it cannot be ruled out that Amoc, the powerful system of ocean currents that helps regulate the climate of northern Europe, will pass a critical tipping point in the coming decades. A risk that begins to become possible at 1.5 degrees of global warming, and then increases for every additional degree the planet warms.
Irreversible effects
When a tipping point is passed, it means that it becomes extremely difficult to reverse the development. This opens up for irreversible effects, and would in this case mean that Amoc sooner or later comes to a halt. Something that would lead to severe cooling, primarily in winter, and more extreme weather in the Nordic region.
The fact that it cannot be entirely ruled out that Amoc reaches this tipping point and collapses before the year 2100 was what prompted the researchers to write their letter to the Nordic governments’ cooperative body. They argued that those in power needed to regard this as a real threat, and prepare accordingly.
SMHI maps what the research says
When the researchers gathered in Finland, it was with this in mind. Together they compiled a report that looked specifically at how a potential Amoc collapse would affect the Nordic region, and one of the institutions that participated was SMHI. They have since taken the work further, and this summer began mapping the state of research to be able to inform policymakers on adaptation and preparedness.
´We have noticed that we are receiving more and more questions about this. Partly because the state of research is changing, but also because the risks have received more attention. So that is why we have felt that we need to gather ourselves around this question in a better way,´says oceanographer Ola Kalén at SMHI.
Major uncertainties remain
Ola Kalén is the one who leads the project at SMHI. But trying to provide a clearer picture of what the research actually says about the risks is no easy task. For even though many recent research studies point to the situation potentially being considerably more serious than IPCC has estimated, there are a smaller number of studies that point in the opposite direction.
´We are very much in agreement that with continued climate change and warming, Amoc will weaken, ´says Ola Kalén.
´But what remains difficult to determine is when such a collapse could occur, and how long it would take to unfold, and it is here that research results diverge.´
Difficult to interpret data
The reason the uncertainty is so great is largely due to the fact that it is a very complicated process that unfolds over a long period of time, but also because the data on which the studies are based is not always straightforward to interpret.
On one hand there is historical so-called proxy data, which is used to represent the strength of Amoc. This can for example involve old samples from corals, through which one can attempt to assess what the temperature of the ocean looked like far back in time. Then there is the observational data being collected now, in situ, out in the Atlantic.
´But these observational records are not very long. They have been ongoing for 30–40 years approximately, and in this context that is a very short time, which makes them difficult to interpret statistically, explains Ola Kalén, ´adding:
´Then looking forward, we have climate models that have quite significant weaknesses in areas around the Arctic, and that means there are quite a lot of uncertainties and different results.´
Only one measure can prevent it
At the same time, it is the uncertainty itself that concerns researchers most – the inability to say with confidence that it will not happen.
´When one talks about risk, one usually talks about a probability and a consequence that together constitute a risk. In this case the probability may be low, but the consequences are so severe that the risk is still considered very high, ´says Ola Kalén.
When the researchers gathered in Finland, it was to highlight the risks of a potential Amoc collapse. In their report they emphasised the need for adaptation plans, early warning systems and long-term financing of ocean observations. But what they primarily pointed to was the need to prevent the potential collapse. Something that can only be achieved in one way.
´The absolute best thing to reduce the risk of this happening is to reduce emissions. So if from now on we can rapidly transition society away from coal, oil and gas, we reduce the risks considerably,´ says Ola Kalén.
Watch the full story to learn more about Amoc and what would constitute the worst case scenario for Sweden.
About Deep Sea Reporter: Our ambition is to examine and report on issues related to the sea and the life that exists beneath its surface. We operate in the public interest and are independent of political, commercial, and other interests in society.
