A cool patch in the North Atlantic may not be a simple thermometer for the strength of a major ocean circulation system. Simulations described in a 2026 Nature Communications paper suggest that the relationship changes as the Atlantic meridional overturning circulation, or AMOC, weakens. That makes the future of the region’s “cold blob” harder to forecast than a steady link between current strength and surface temperature would imply.
The cold blob, also called the North Atlantic warming hole, covers about 965,000 square miles south and southeast of Greenland. The report says it cooled by as much as 1.8 degrees Fahrenheit over the past century even as other ocean waters warmed. A Phys.org report by Adam Smeltz, edited by Robert Egan, summarizes the research. The team included researchers from Penn State’s College of Earth and Mineral Sciences. Yifei Fan is identified as lead author of the paper, and Laifang Li as its corresponding author.
AMOC is a large-scale circulation that carries warm surface water north and colder, denser water south in the deep ocean. A weaker circulation can contribute to cooling south of Greenland and Iceland while other regions warm. But the researchers caution that the connection between AMOC strength and the cold blob’s surface temperatures is more irregular over time than commonly assumed. Direct AMOC observations extend back only about two decades, limiting historical analysis.
To examine how the relationship might vary, the team analyzed simulations spanning decades and a range of scenarios. These included different greenhouse-gas concentrations and climate conditions representing past and present environments. The simulations accounted for heat moving within the ocean, heat exchange between ocean and atmosphere, and heat radiated from the air, including effects associated with low clouds.
The analysis found three phases in the simulated cooling response. When the current weakened from its strongest state, surface temperatures fell modestly. When it weakened from a midrange strength, the temperature drop was roughly three times larger, and the cold blob expanded across the subpolar basin. But when weakening began from an already diminished state, the cooling effect faded and the cool region shifted northeast toward Iceland and the Norwegian Sea. The researchers pointed to changing atmospheric radiation and reflections from low clouds as contributing factors.
That changing response matters for estimates of how much heat the North Atlantic can take up. Fan said that once AMOC weakens enough, the ocean may absorb more heat from the atmosphere and approach its capacity to buffer climate change. The paper’s simulations suggest the circulation could move from a higher-strength phase today to its lowest-strength phase by 2100. They place the timing of the cold blob’s most significant temperature shift anywhere from as early as 2021 to as late as 2067, underscoring the uncertainty in the projection.
Those dates are model-based estimates, not a timetable established by ocean temperatures alone. The report stresses that surface temperature changes do not, by themselves, prove what the current is doing, and that a changing cold blob does not necessarily signal an AMOC collapse. Li said further study and sustained Earth-system monitoring, including ocean temperature readings, could help narrow the range of scenarios and improve forecasts of North Atlantic climate patterns. Better forecasts could help clarify when key temperature thresholds might be reached and inform planning around climate mitigation.
<a href="https://phys.org/news/2026-11-north-atlantic-cold-blob-climate.html">Source: Phys.org report</a>