by Alexey Mishonov
The Atlantic Meridional Overturning Circulation (AMOC) is a vast ocean current system crucial for regulating the Earth’s climate, and it has been observed to slow down due to ongoing climate change. Some scientists speculate that it could collapse, potentially wreaking havoc on the global climate. However, new research from the University of Maryland and the National Oceanic and Atmospheric Administration (NOAA) indicates that the system may be more resilient to collapse than previously believed.
The AMOC is a crucial part of the global meridional overturning circulation, functioning like a conveyor belt that helps regulate Earth’s climate by transporting warm, salty water northward and cold, fresh water southward. The upper branch of the AMOC transports warm, salty surface water to the deep convection sites in the subpolar North Atlantic and Nordic Seas, where it cools and sinks into the deep ocean, forming the deep-ocean branch of the AMOC. The formation of deep water relies on the surface layer becoming denser than that of the underlying layers.
The efficiency of this mechanism hinges on several factors, one of which is the position of the subpolar front. This position dictates how far north the surface water within the AMOC can extend, thereby facilitating deepwater formation. Scientists are concerned that rising ocean temperatures, coupled with the potential freshening of the subpolar surface due to melting Arctic sea ice, may impede deepwater formation, leading to a severe weakening or even collapse of the AMOC. These changes are believed to manifest as significant shifts in the thermohaline structure and currents in the subpolar North Atlantic, with a shift in the subpolar front’s position serving as a precursor to the curtailment or even collapse of the AMOC.
“The climate is so reliant on the AMOC that any significant alteration could drastically impact the global thermohaline circulation, and consequently, the global climate,” wrote the authors of a paper recently published in Climate. Alexey Mishonov, a co-author of this publication, is a research scientist at UMD’s Earth System Science Interdisciplinary Center (ESSIC) with extensive expertise in various oceanography fields.
Mishonov and his colleagues at NOAA’s National Centers for Environmental Information examined decadal averages of temperature, salinity, and density data spanning the past seventy years. They also assessed wind stress and sea surface elevation data from the last thirty years. By integrating these analyses, they discovered that although there are clear signs of some AMOC deceleration over the past two decades, the system has demonstrated remarkable resilience to ongoing ocean warming over the long term.
The changes observed so far have been relatively modest, according to Mishonov. Over the past 30 years, the average current speeds in the upper ocean layers have declined by less than 10–15%, and this slowdown was uneven across the North Atlantic region. They also found that the shift in the critical boundary between colder and warmer waters was limited, moving by at most 3 ° latitude over 70 years in some years. These findings suggest that the AMOC has remained comparatively stable, with no major changes in its position or strength.
“Although the AMOC is vulnerable to some deceleration due to ongoing surface warming and/or high-latitude freshening, it may also possess enough resilience to endure these changes,” Mishonov says, “While it cannot be entirely dismissed that the AMOC might reach its tipping point within this century, [our analysis] suggests that such a collapse is unlikely.” The Earth’s climate system is a complex, nonlinear entity that exists far from equilibrium. In such systems, abrupt changes, known as bifurcations, can occur. This year, one of the authors, Dan Seidov, published a new paper in the journal Water, which explains how these unanticipated abrupt changes can take place (Seidov, D., Self-Organization of Ocean Circulation: A Synergetic Perspective on Ocean and Climate Dynamics, Water 2026, 18(7), 774, https://doi.org/10). The keyword here is “unanticipated,” says Mishonov.
Using the findings of this research, the authors aim to revisit the decadal climate variability in the North Atlantic and build a more unified understanding. They will focus on what long-term AMOC records alone can tell us about the AMOC and its role in the climate system.
