Thermohaline Circulation Dynamics in Climate Systems

Thermohaline circulation refers to the global system of ocean currents driven by variations in water density, itself controlled by temperature (thermo) and salinity (haline). This “global conveyor belt” transports vast amounts of heat and dissolved carbon, regulating climate on regional and planetary scales. In the Atlantic, the Meridional Overturning Circulation (AMOC) carries warm surface waters northward and returns cold, dense waters southward at depth, influencing European climate and tropical precipitation patterns. Dynamical feedbacks between ocean stratification, wind‐driven upwelling in the Southern Ocean and freshwater inputs from ice melt or river discharge shape its stability. Under increasing greenhouse gas forcing, models project a weakening of overturning strength and reduced poleward heat transport, with implications for heat redistribution, sea level and biogeochemical cycles. Uncertainties remain in threshold behaviour, potential tipping points and inter‐basin compensations through Pacific overturning changes. Understanding resilience mechanisms, early warning indicators and the interplay of atmospheric teleconnections is essential for robust projections and adaptation strategies.

Research from Nature Portfolio

Recent studies demonstrate the remarkable resilience of the AMOC under extreme greenhouse‐gas and freshwater perturbations. A multimodel assessment reveals that persistent Southern Ocean upwelling sustains a weakened but continuous overturning, and that a compensating Pacific overturning branch fails to fully offset Southern upwelling, rendering a complete Atlantic collapse unlikely within this century. Complementary work using CMIP5 and CMIP6 projections quantifies a systematic decrease in poleward ocean heat transport across both hemispheres, driven primarily by overturning decline and upper‐ocean warming, with stronger reductions in the latest generation of models. Another line of investigation examines the climatic teleconnections of a potential AMOC collapse, showing that although such a collapse would have global downsides, it could locally stabilise eastern Amazonian rainfall and temperature, illustrating the complexity of climate–biosphere interactions and the need to weigh regional resilience against broader risks.

Research from all publishers

A comprehensive synthesis grounded in dynamical systems theory reappraises the equilibrium stability of the AMOC, concluding that multiple stable states remain plausible but that the location of present‐day thresholds is highly uncertain. This framework highlights the urgent need for observable metrics to distinguish between a gradual slowdown and a critical transition. Historical simulations from CMIP6 reveal that anthropogenic aerosol forcing likely induced a substantial strengthening of the AMOC between 1850 and 1985, a response more pronounced than in earlier model phases; observational constraints, however, suggest that both forcing and overturning trends may be overestimated. A conceptual network study of interacting tipping elements—including polar ice sheets, the AMOC and tropical forests—shows that the AMOC often acts as a mediator of cascading impacts, transmitting destabilising signals between ice‐sheet thresholds and rainforest dynamics, thereby increasing the risk of domino effects under continued warming.

Thermohaline Circulation Dynamics in Climate Systems publication trend

The graph below shows the total number of articles in thermohaline circulation dynamics in climate systems across all publications each year (not limited to Nature Index journals).

Technical terms

Thermohaline circulation: A global system of ocean currents driven by density gradients arising from temperature and salinity variations.

Atlantic Meridional Overturning Circulation (AMOC): The component of thermohaline circulation in the Atlantic that transports warm surface waters northward and returns cold deep waters southward.

Ocean heat transport: The movement of thermal energy by ocean currents, crucial for redistributing heat from the equator toward the poles.

Freshwater forcing: Input of low‐salinity water (from ice melt or river discharge) that alters ocean density and can affect circulation strength.

Tipping element: A component of the climate system that can undergo a rapid transition to a qualitatively different state when critical thresholds are crossed.

References

1. Continued Atlantic overturning circulation even under climate extremes. Nature (2025).
2. The decrease in ocean heat transport in response to global warming. Nature Climate Change (2023).
3. A potential collapse of the Atlantic Meridional Overturning Circulation may stabilise eastern Amazonian rainforests. Communications Earth & Environment (2023).
4. Stability of the Atlantic Meridional Overturning Circulation: A Review and Synthesis. Journal of Geophysical Research - Oceans (2019).
5. Aerosol‐Forced AMOC Changes in CMIP6 Historical Simulations. Geophysical Research Letters (2020).
6. Interacting tipping elements increase risk of climate domino effects under global warming. Earth System Dynamics (2021).