Amoc and how climate change
Executive summary
The Atlantic Meridional Overturning Circulation (AMOC) is a major ocean current system that transports heat and salt through the Atlantic and helps shape regional climates; observations and models show it has weakened and is likely to weaken further under warming [1] [2] [3]. Scientists disagree on whether climate change will push the AMOC past a rapid “tipping point” this century: some modeling and indicator studies flag a real risk of collapse by mid-to-late century under continued emissions [4] [5], while other high-profile studies and model syntheses find collapse unlikely though weakening is expected [6] [7] [8].
1. What the AMOC is and why it matters
The AMOC is the Atlantic branch of global overturning circulation that carries warm surface waters north and returns cold, dense waters south at depth, thereby redistributing heat, influencing European winters, Atlantic storm tracks, the West African monsoon and sea-level patterns along the U.S. East Coast [1] [9] [10]. Its role in ventilating the ocean also affects carbon storage and ocean chemistry, meaning large AMOC shifts would alter regional climates and biogeochemical cycles [11] [3].
2. What observations are telling us now
Direct measurements and proxy-based studies indicate the AMOC has slowed relative to mid‑20th-century estimates and that North Atlantic ventilation has “aged” over the past three decades—an observational signal that, when combined with models, points to a climate-driven component to the slowdown [2] [3] [1]. Short observational records and natural variability complicate attribution, but multiple independent analyses find evidence of weakening [2] [3].
3. How climate change can weaken or tip the AMOC
Warming-driven freshwater input (melting Greenland ice, increased precipitation) reduces surface salinity and density in the subpolar North Atlantic, diminishing the sinking that powers the AMOC; models show sustained freshwater forcing can push the circulation into a much weaker, shallower state or even an abrupt collapse—classical tipping behavior that has precedent in past glacial events [5] [12] [11]. Climate‑model experiments and physics‑based indicators have been developed to detect the onset of such tipping events [4] [5].
4. How likely is a collapse this century? Competing scientific views
There is no consensus. A multi‑model analysis and targeted CESM experiments produced physics‑based indicators suggesting the AMOC could begin to collapse mid‑century under intermediate to high emission scenarios [4] [5]. Conversely, large model intercomparisons and theoretical work suggest the AMOC is more resilient—stabilizing mechanisms like wind‑driven upwelling and interbasin pathways make an imminent collapse unlikely, though weakening with important impacts is expected [6] [7] [8]. Major organizations flag it as a plausible tipping point but stress wide uncertainty in timing and magnitude [1] [12].
5. If the AMOC weakens or collapses, what would change?
Model experiments and paleoclimate analogues point to regional cooling in Northern Europe, altered storminess and rainfall patterns (including Amazon and Sahel changes), faster relative sea‑level rise on the U.S. East Coast, and disruptions to ocean carbon cycling; the precise pattern and global magnitude depend on whether change is gradual or abrupt [1] [9] [11] [10]. Some assessments emphasize catastrophic, hard‑to‑adapt shifts if a true collapse occurs, while others note impacts would be superimposed on broader anthropogenic warming [1] [6].
6. What this means for policy and research priorities
Given the mix of evidence—observed weakening, plausible mechanisms for tipping, but large intermodel spread—policy prescriptions converge on rapid emissions reductions to lower the probability of extreme AMOC outcomes and on expanded, sustained observation networks and targeted modeling to shrink uncertainties [12] [2] [4]. Scientists also call for development of early‑warning indicators and for planning that accounts for both a likely gradual weakening and low‑probability high‑impact collapse scenarios [5] [4] [6].