An important current system in the Atlantic Ocean may have lost so much stability that it could collapse, according to research. This could have dramatic consequences for the global climate.
An important Atlantic current, which includes the Gulf Stream, maybe approaching a critical threshold. The Atlantic Overcurrent (AMOC), which is responsible for the exchange of warm and cold water masses in the ocean and thus also influences the climate in Europe, may have lost stability. This is what Niklas Boers from the Potsdam Institute for Climate Impact Research (PIK) writes in the scientific journal “Nature Climate Change”.
Europe’s climate, in particular, would be extremely affected
The Atlantic overturning circulation is a complex current system that transports warm water from the tropics at the ocean surface towards the north and cold water at greater depths towards the south. In Western Europe, this circulation ensures comparatively mild temperatures, and it also has an impact on other regions of the world. A collapse of this important system would have serious consequences for the global and especially the European climate.
According to Boers, the circulation is “one of the most important circulation systems on our planet” and is currently “weaker than at any time in the past 1000 years”. However, it is unclear whether this is just a change in the mean circulation state or a real loss of dynamic stability – and this difference is crucial, Boers explains in a PIK release. A reduction instability would mean that the Atlantic current has approached the critical threshold beyond which the circulation system could collapse.
To shed light on this, Boers looked at so-called fingerprints in temperature and salinity patterns on the Atlantic surface. “A detailed analysis of these fingerprints in eight independent indices now suggests that the weakening of the AMOC over the last century is indeed likely associated with a loss of stability,” PIK writes in this regard.
Loss of stability comes “earlier and more clearly than expected”
Factors affecting the flow, besides the direct effects of Atlantic warming, include freshwater inflows from melting ice masses, increasing precipitation, and water from rivers. “I would not have expected that the additional amounts of fresh water that flowed into the ocean over the last century would already cause such a response from the AMOC,” Boers explained. Therefore, existing models “urgently need to be brought into line” with the available observations “to assess how far the AMOC actually still is from the critical threshold”. Even if the respective importance of the various factors needed to be further investigated, they were in any case “linked to human-induced climate change”.
Boers explained to the Deutsche Presse-Agentur that it is very difficult to estimate exactly when the current will weaken. “It depends first of all on how much CO2 is released and how much temperatures rise as a result.” In addition, there are uncertainties about how much warmer it will be in the Arctic and how much the freshwater flow into the Atlantic will increase due to the temperature rise.
The crucial point of the study is that “we are seeing – earlier and more clearly than expected – clear signs of loss of stability”, Boers stressed. “That is, the system is moving towards the critical threshold, and every gram of CO2 that is still being released increases the probability that the AMOC will eventually reach the critical value.” If the critical point is exceeded, the AMOC will largely come to a standstill within a few decades, he said.