“Switching off” Atlantic currents could have devastating consequences

The 44 authors of the letter addressed to the Nordic Council of Ministers include Professor Michael Mann from the USA, who has contributed to the scientific understanding of historical climate changes based on temperature data from the last thousand years. The letter was also signed by German oceanographer Professor Stefan Rahmstorf, who specializes in researching the relationship between climate and ocean circulation. Climatologists have been warning for several years that global warming could drastically change currents in the North Atlantic, but this is the first time they have issued a warning directly to governments.

Ocean currents are created in ocean waters by differences in water temperature, salinity and density. Water heated near the equator flows towards the pole, cooling along the way, and then its greater salinity and density cause it to sink lower and return to the equator, where it warms up again. This makes it cooler at the equator and warmer in the polar regions. For this mechanism to work efficiently, differences in water temperature and salinity are necessary. If heat transport by ocean currents stops, the polar regions will become dangerously warm and the equatorial regions will become warmer. Greenhouse gas emissions increase the average global temperature. More fresh water then flows into the Atlantic (from melting glaciers, especially in Greenland, and due to heavier rainfall). The increased inflow of freshwater may lead to the “switching off” of the Atlantic Meridional Overturning Circulation (AMOC). As the authors write, a series of scientific studies conducted over the last few years suggest that this risk has so far been significantly underestimated. Such a change in ocean circulation would have devastating and irreversible consequences, especially for the Nordic countries, but also for other parts of the world. Increasing evidence shows that the Arctic region is crucial to climate regulation across the planet. The Greenland Ice Sheet, the Barents Sea ice, the boreal permafrost systems, the subpolar deep-sea gyre, and the Atlantic Meridional Overturning Circulation (AMOC) are susceptible to large, interconnected, nonlinear changes. The AMOC, which is the dominant northward heat transport mechanism in the North Atlantic, determines the living conditions of all people in the Arctic region and beyond and is increasingly at risk of exceeding a tipping point. The risk of exceeding the critical point is real, researchers report. The average global temperature may exceed 2.5 degrees C much faster. Thus, the goal of the Paris Agreement to limit global warming to below 2 degrees C and keeping it at 1.5 degrees C will not be achieved.

The 2023 report of the Intergovernmental Panel on Climate Change (IPCC) concluded with high confidence that the likelihood of abrupt or irreversible changes to the climate system will increase with levels of global warming; the probability of previously rare phenomena that are associated with potentially very large negative effects is also increasing. A recent report by the Organization for Economic Co-operation and Development (OECD) concluded that “current scientific evidence clearly supports unprecedented, urgent and ambitious climate action to address climate system tipping risks.” In 2023, the IPCC hoped that the Atlantic circulation would not break down dramatically by 2100 – but if it did, it would most likely “cause sudden changes in regional weather patterns and have a major impact on ecosystems and human activities.” Research since the last IPCC report suggests that this risk has previously been underestimated and that the tipping point may be exceeded within the next few decades. However, despite the significant research conducted in this area, the likelihood of such an event remains highly uncertain. The authors of the open letter want to draw attention to the fact that the possibility of a collapse of the AMOC circulation this century still remains open. It is even more likely that the collapse will occur this century but will not fully develop until the next. Therefore, this threat should be taken seriously. Even the average probability of catastrophic events affecting the entire world for centuries to come requires more to be done to minimize risk.

In the case of the Nordic countries, the effects would likely be catastrophic, including significant cooling in the region while surrounding regions would warm. This would expand and deepen the “cold spot” that has already developed over the subpolar Atlantic Ocean. This would likely lead to unprecedented extreme weather conditions. Although the effects on weather patterns, ecosystems and human activities require further study, the changes would likely threaten agriculture in northwestern Europe. Many further impacts are likely to be felt around the world, including shifting tropical rainfall patterns, reduced absorption of carbon dioxide by the oceans (and therefore faster increases in atmospheric carbon dioxide levels), as well as significant additional sea level rise, particularly along the US Atlantic coast and ” “shock” to marine ecosystems and fisheries. Recognizing that it is impossible to adapt to such a major climate catastrophe, the authors call on the Nordic Council of Ministers to initiate an assessment of this significant risk for the Nordic countries and take steps to minimize this risk as much as possible. This could include leveraging the strong international position of the Nordic countries to increase pressure for greater urgency and priority in global efforts to reduce emissions as quickly as possible, as quickly as possible, to stay close to the 1.5C target set out in the Paris Agreement.