Scientists warn AMOC weakening risk

New Scientist and the Potsdam Institute for Climate Impact Research amplified fresh warnings on May 19 and May 20 that the Atlantic Meridional Overturning Circulation, or AMOC, is weakening as the planet warms. The AMOC is a large system of Atlantic currents that transports heat northward and returns colder, denser water at depth, helping shape climate patterns in Europe, the tropics and the North Atlantic. Recent reporting and papers do not say a collapse is imminent, but they do point to a mounting body of observational and modeling evidence that the circulation is slowing under greenhouse warming and freshwater input. ### What exactly did the new evidence show? New Scientist reported on April 8 that buoy measurements at four latitudes in the western Atlantic showed the AMOC slowing, calling them the strongest evidence yet that the system is weakening. The report said the measurements came from moorings spanning multiple parts of the Atlantic overturning system rather than from a single latitude, which has been a longstanding limit in direct observation. (newscientist.com) Nature Geoscience and related observational work have also tied recent ocean changes to a weaker overturning circulation. One paper said the AMOC is the main driver of northward heat transport in the Atlantic today, while another found the abyssal limb in the North Atlantic had weakened over the past two decades based on moorings and hydrographic data. ### Why does freshwater matter so much? (newscientist.com) Egusphere researchers wrote that AMOC tipping in models depends strongly on freshwater forcing. The mechanism is straightforward: added freshwater from rainfall, river discharge, sea-ice melt or Greenland ice melt lowers salinity in the North Atlantic, making surface waters less dense and less likely to sink, which weakens the overturning circulation that depends on dense water formation. (nature.com) PIK said on April 20 that a strengthening Nordic Seas overturning circulation could be a direct consequence of AMOC weakening from global warming rather than an unrelated anomaly. That study described a feedback mechanism linking changes in northern Atlantic circulation to broader overturning shifts. (egusphere.copernicus.org) ### What climate effects are scientists linking to a slower AMOC? A PIK release on August 28, 2025 said high-emissions simulations produced a possible AMOC shutdown after 2100 and linked that outcome to reduced northward ocean heat transport, summer drying and severe winter extremes in northwestern Europe, and shifts in tropical rainfall belts. The study described those effects as outcomes in a high-emissions future, not as present-day observations. (pik-potsdam.de) A Nature Communications study published this month found that a weakening AMOC would increase the frequency of atmospheric rivers in the North Atlantic and Europe in twenty-first-century climate model projections. Another Nature study linked a weakened AMOC to the North Atlantic warming hole, a region of relative cooling in the subpolar Atlantic. ### Are scientists saying collapse is certain this century? (pik-potsdam.de) Nature published a paper in late 2024 saying climate models suggested the AMOC was unlikely to collapse this century because of stabilization from Southern Ocean wind-driven upwelling. That paper stands alongside other studies highlighting substantial weakening, tipping behavior in some models, or shutdown risks after 2100 under high emissions. (nature.com) New Scientist’s recent coverage and PIK’s posts reflect that split in the literature: strong concern about weakening, active debate over the timing and probability of collapse, and close attention to salinity, deep-water formation and long-term model behavior. That is an inference from the mix of studies and summaries now in circulation. (nature.com) ### What are researchers watching next? PIK’s April 7 release said an AMOC collapse could turn the Southern Ocean into a carbon source and add about 0.2 degrees Celsius of extra warming over long timescales through ocean carbon release. Nature Communications Earth & Environment published the underlying study, which modeled the carbon response under an AMOC shutdown scenario. (newscientist.com) The next markers are likely to come from updated buoy observations, salinity trends in the North Atlantic, Greenland meltwater estimates and new model intercomparisons. PIK’s AMOC releases and peer-reviewed journals including Nature titles and Copernicus publications are where many of those updates are appearing. (newscientist.com) (pik-potsdam.de)