New knowledge about Northern Europe's radiator: Volcanic eruptions in the past may have pushed ocean currents towards collapse

If it goes down, Denmark's climate could change dramatically. The AMOC, Atlantic Meridional Overturning Circulation, pumps warm water from the southern hemisphere towards the north and is crucial to ensuring a warm and mild climate in Denmark. That is why it is also called Northern Europe's radiator. If it collapses, the Danish climate could change to something resembling that of Alaska, with winter temperatures down to minus 35 degrees.  

However, global warming and the larger amounts of meltwater from the Arctic threaten the stability of the ocean current and its ability to pump warm water from the south to the north. However, scientists around the world continue to disagree on how bad the situation is, how great the risk of a complete collapse of the ocean current is, and how quickly it could happen.

In a new study conducted by an international team of researchers from, among others, the Niels Bohr Institute at the University of Copenhagen, the researchers are now adding another element to the pool of things that can cause the AMOC ocean current to change: volcanic eruptions.

“Our study shows that the AMOC may be far more sensitive to external influences, such as volcanic eruptions, than we previously thought. This provides important insight into how the system may also react in the future,” says Professor Markus Jochum from the Niels Bohr Institute, who is the last author of the study.

May explain sudden climate change

By combining data from ice cores with hundreds of climate models, the team of researchers has shown how extreme volcanic eruptions can throw the climate system out of balance and push the important AMOC ocean current into a weakened or completely collapsed state.

“We show that large volcanic eruptions near the equator have historically been able to cause a collapse in the Atlantic Ocean current, which in turn could trigger sudden climate changes that lasted for thousands of years,” says lead author Guido Vettoretti from the Niels Bohr Institute.

Large volcanic eruptions send sulphur and dust into the atmosphere and stratosphere, which prevents the sun from warming the Earth. This sets off a cold chain reaction that leads to, among other things, more sea ice and a change in the salinity of the ocean, which ultimately puts the ‘pump’ in the AMOC out of operation.

The last ice age ended over 10,000 years ago, but lasted for 100,000 years, during which there were repeated sudden shifts between cold and warm periods – the so-called Dansgaard-Oeschger events. These are climate events whose causes have long been debated by scientists.

Here, the new study shows that very large volcanic eruptions could be the very cause that significantly changes the climate for centuries or millennia – especially if the climate has already approached a critical point, as we are seeing in our age of global warming.

“It's like tilting a balance board – if the system is close to a tipping point, only a small push is needed. Our model shows that a volcanic eruption can be that push,” explains Professor Markus Jochum, who is the last author of the study.