The Atlantic Ocean current, of which the Gulf Stream is a part, seems to be much more unstable than previously thought. With a weakening of the Gulf Stream, Europe will become the odd one out in a warming world: it will warm less than other places or even become colder, especially in winter. Meanwhile, the rest of the world warms up. A new study has investigated how temperature extremes in Europe may change as a result.

The Atlantic Ocean current is less stable than thought 

According to the most recent IPCC report from 2021, the risk of a collapse of the Atlantic Meridional Overturning Circulation (AMOC) this century is low. However, since then, there have been increasing indications that the current AMOC is much more sensitive than thought.  

Due to the increasing amount of precipitation and the melting of the Greenland ice sheet, the water in the North Atlantic Ocean is becoming less salty and therefore less dense. Normally, the salty and cold, and thus relatively heavy water near Greenland sinks to the deep sea. This sinking of water is the driving force of the AMOC, but it is becoming weaker due to climate change. 

The outlook for Europe 

What this means for future temperature extremes in Europe has been investigated in a new study by Utrecht University and the KNMI. Various conditions were calculated using a climate model. The amount of fresh water entering the North Atlantic Ocean is crucial for the strength of the AMOC. This varies in the model between a high and a low value, which can be seen as a small push or a strong push against the AMOC system. Additionally, two different emission scenarios for the future were calculated: a moderate emission scenario (RCP4.5) and a high emission scenario (RCP8.5). The expected global warming in 2100 is projected to be 2.7 and 4.7 degrees respectively compared to the late 19th century.

Colder winters 

If the winter months become colder due to a weaker AMOC, sea ice will expand southward. Since sea ice, unlike the dark ocean surface, reflects a lot of sunlight, this enhances the cooling. According to this new study, under a moderate emission scenario (RCP4.5), sea ice could even advance into the North Sea in winter if the AMOC collapses (see image 1). As a result, our winters will become much colder (see image 2).

Especially the minimum temperatures will take a significant plunge: the once-in-10-years cold extremes in winter could be about 15 degrees lower in the Netherlands. The average winter temperature will be about 3 degrees below pre-industrial levels. The temperature in summer will not be significantly affected by the collapse of the AMOC (see image 3).

If emissions continue to rise (RCP8.5), the likelihood of the AMOC collapsing increases (even a small push is enough), but the impact on European temperatures is smaller. This is mainly because in that scenario, the seawater becomes so warm due to the increased CO2 concentration that the sea ice cannot expand significantly southward. As a result, the cold extremes are dampened compared to a scenario where the sea ice does reach the European coast. These scenarios vary widely in terms of their impact on winter temperatures in Northwestern Europe.