The Atlantic Meridional Overturning Circulation (AMOC), a crucial ocean current system, may be on the verge of collapsing, according to multiple reports. University of Bordeaux scientists have found that AMOC is on track to weaken by 50% by the end of this century, a sharp increase from previous estimates of around 32% over the same period. The new study, published in Science Advances, corrects earlier biases in ocean surface temperature and salinity, which had led to overly optimistic assumptions. The researchers noticed a bias in salinity levels for the surface of the South Atlantic, and their new model sharply increased the expected rate of slowdown. Previous studies had underestimated how fast AMOC is slowing, as earlier simulations assumed a steeper salinity gradient between polar and surrounding waters than actually exists.
An AMOC collapse would have severe consequences. According to University of Bordeaux scientists, it could lead to 'extensive drying' in Africa's Sahel region. Multiple reports indicate that temperatures in the Northern Hemisphere would plummet as the Gulf Stream fails to bring warm water from the Tropics. UK winters could become up to 7°C colder on average, according to major media reports. Robust effects of an AMOC collapse, as reported in the Nordic report, include general cooling of the North Atlantic and surrounding areas, sea level rise in northern Europe, and changes in tropical precipitation patterns. The main and dominant signal would be cooling compared to the warming level at the time of collapse, though other effects, such as the extent of winter and summer cooling, are more uncertain.
In response to this threat, Utrecht University researchers have proposed closing the Bering Strait as a potential solution. The Bering Strait is a 53-mile (82 km) wide international waterway separating Russia and Alaska. According to the researchers, a constructed closure would alter the balance of freshwater in the system, acting as a stabilizer. The proposed dam would be 50 miles (80 km) long and 330 feet (100 m) wide at the top, according to major media reports. However, the closure would have a 'large impact' on local ecosystems, the researchers noted. In a press release, they stated that a possible collapse would have a major impact on the global climate, particularly Europe's, and could be practically irreversible. They added that constructing this closure could be a feasible climate intervention strategy to prevent an AMOC collapse. However, they stressed that carbon dioxide mitigation efforts are the preferable option to prevent an AMOC collapse, and that the dam is only a backup if those efforts fail.
The IPCC 2023 report states with 'high confidence' that continued global warming will lead to a weakening of AMOC, but with 'medium confidence' not to an abrupt and complete collapse before 2100. A separate report, 'A Nordic Perspective on AMOC Tipping,' summarizes current scientific knowledge on consequences of a possible rapid weakening or collapse. It identifies important knowledge gaps, especially regarding sector-specific consequences for food production, energy systems, and other climate-sensitive sectors in Nordic countries. The report recommends pushing for powerful emission reductions to achieve goals of reduced fossil use, net-zero emissions, and negative emissions. It also calls for securing long-term financing to maintain central observation networks and build an early warning system for AMOC. An AMOC collapse could trigger extreme consequences in Nordic countries that differ from and partly counteract those expected from global climate change, according to the report.
Fresh water from melting glaciers is slowing the AMOC's flow, according to multiple reports. This influx of freshwater reduces the salinity and density of surface waters, hindering the sinking process that drives the circulation. The exact timeline for a potential collapse remains uncertain, and the reliability of the new models is still debated. The specific regional impacts on Nordic countries are also unclear, as are the technical and political feasibility of the proposed Bering Strait dam and its full ecological consequences.