We welcome all contributions that investigate changes in the AMOC and their Earth System impacts. These can include direct physical impacts, such as atmospheric, oceanic, or cryospheric; biogeochemical as well as marine and terrestrial ecosystem responses; and socioeconomic impacts, such as health, agricultural, and economic repercussions. Contributions can cover any timescale, from paleoclimate and the recent past to future projections, from seasonal and decadal changes to long-term (centennial to millennial), both past and future. In addition, the AMOC can be studied in a range of settings, from internal variability to forced trends or abrupt/tipping behaviour, affecting both mean and extreme variables.
We call for contributions employing a broad range of tools, from Earth System, regional, and simple models to reanalyses and observations/proxies, as well as socioeconomic and impact-related models. Finally, as the Atlantic subpolar gyre (SPG) is an ocean system whose strength, stability, and impact on the climate are strongly connected to the AMOC, we also welcome contributions discussing the impacts of SPG changes on the Earth System.
During the Ice Ages, abrupt climate changes co-occurred with switches in Atlantic Meridional Overturning Circulation (AMOC) strength. The thermal bipolar seesaw has served as a seminal conceptual framework to explain the global extent of these events, calling on interhemispheric redistribution of heat to explain the observed north-south temperature pattern. Here we summarize an emerging alternative framework centered instead on the global ocean heat content (OHC) and planetary energy budget, which we illustrate using simulations of spontaneous abrupt climate change in three climate models. In all models, the AMOC strength sets the OHC trend via the rate of North Atlantic heat loss, coupled to the top-of-the-atmosphere energy budget through radiative feedbacks. Antarctic and Greenland temperatures, as recorded in ice cores, are shown to reflect OHC and the rate of North-Atlantic heat loss, respectively. Under intermediate glacial climate states, global ocean heat uptake cannot reach steady-state with the bimodal rate of North Atlantic heat loss causing instability. Our synthesis suggests that the AMOC serves as a heat valve that alters planetary temperature by changing the radiative balance. This implies amplified planetary heat uptake in response to projected future AMOC weakening.
How to cite: Buizert, C., Abe-Ouchi, A., Vettoretti, G., Zhang, X., Kuniyoshi, Y., Shackleton, S., Rasmussen, S., Pedro, J., Galbraith, E., and Stocker, T.: The ocean heat valve: AMOC and planetary energy budget during abrupt glacial climate change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1465, https://doi.org/10.5194/egusphere-egu26-1465, 2026.
The Atlantic meridional overturning circulation (AMOC) is a vitally important component of the global ocean circulation because of its impact on the environment, weather, and ecosystems. The South Atlantic is a key gateway for water mass exchanges between the Atlantic and other basins as southward overturning freshwater transport at 34.5°S increases the likelihood of an AMOC collapse in the future. In two-thirds of state-of-the-art coupled climate models, the overturning freshwater transport at 34.5°S is northward and AMOC is monostable, whereas most observations find that freshwater transport is southward suggesting AMOC is bistable. The upper limb of the AMOC and Deep Western Boundary Current (DWBC), a major element of AMOC’s lower limb, control freshwater transport at 34.5°S. It is therefore crucial to observe the daily strength of both of these circulation systems and use these observations to validate numerical models.
We examine AMOC and DWBC variability from over fourteen years of South Atlantic MOC Basin-wide Array (SAMBA) measurements between South America and South Africa along 34.5°S . These observational records enable concurrent examination of the temporal variations of the upper and lower limbs of AMOC. During 2009-2022, the AMOC volume transport weakened by -0.6 Sv/yr, but this trend is obscured by significant higher frequency variability (± 10 Sv standard deviation with respect to the 18.6 Sv long-term mean) and a 3-year data gap on the eastern boundary during 2010-2013. The inclusion of more years of data has shifted the AMOC seasonal cycle from semi-annual to quasi-annual, and has improved agreement with Argo-altimetry based estimates on seasonal timescales. SAMBA transports are more energetic than Argo-altimetry on intraseasonal and interannual time scales, with the largest differences occurring when SAMBA density-driven variations are strong. The SAMBA DWBC has a mean southward transport of -17 Sv and a standard deviation of 22 Sv, with a significant negative trend of -0.3 Sv/year (DWBC increasing in strength). AMOC and DWBC variations are modestly correlated along 34.5°S on monthly and longer timescales, such that a weaker AMOC corresponds to stronger DWBC anomalies. This covariability will be explored further to better establish the connectivity between AMOC and the DWBC in the South Atlantic.
How to cite: Perez, R. C., Dong, S., Ansorge, I., Campos, E., Chidichimo, M. P., Garcia, R., Lamont, T., Louw, G., Le Henaff, M., Piola, A., Sato, O., Speich, S., Tuchen, F. P., van den Berg, M., and Volkov, D.: Observed Variability of the Atlantic Meridional Overturning Circulation and the Deep Western Boundary Current along 34.5°S, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13099, https://doi.org/10.5194/egusphere-egu26-13099, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) plays an important role in regulating the global climate. The AMOC change in response to global warming has important environmental and, potentially, societal impacts but remains an issue with large uncertainty. Here we use a series of coupled climate model experiments to reveal the overlooked role of Atlantic subtropical salinification, a robust consequence of an intensified hydrological cycle, in inhibiting AMOC weakening under global warming. Without subtropical salinification, the AMOC weakening more than doubles in response to a doubling of CO2, primarily driven by a reduced zonal salinity gradient that weakens the geostrophic component of AMOC through the thermal wind relation. This larger AMOC weakening reduces surface warming in the Northern Hemisphere by as much as 1–3 K at northern high latitudes when subtropical salinification is inhibited.
How to cite: Liu, M., Soden, B., and Vecchi, G.: Greenhouse gas-induced Atlantic subtropical salinification partly offsets a large decline in the AMOC, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18907, https://doi.org/10.5194/egusphere-egu26-18907, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the climate system, yet the consequences of a pronounced weakening under emission pathways consistent with the Paris Agreement remain poorly understood. Using the comprehensive GFDL ESM2M Earth System Model with the Adaptive Emissions Reduction Approach, we impose a freshwater-induced strong AMOC weakening to 20% of its preindustrial strength starting in year 2026. These simulations otherwise follow a pathway in which global warming stabilizes at 2°C and the AMOC weakens only modestly and partially recovers. Relative to the modest-weakening scenario, a strong AMOC weakening cools global mean surface air temperature by −0.8°C (5-member ensemble range: −0.7 to −0.9) by 2171-2200, with pronounced regional cooling in the North Atlantic, reaching up to −6.8 °C (−4.1 to −9.7) in winter over Iceland. The ocean stores an additional 385 ZJ (331–428) of heat, primarily south of 20°N, associated with reduced northward heat transport and enhanced heat uptake in the North Atlantic. The additional heat increases global thermosteric sea level rise by 10% (8–12). Atmospheric CO2 declines by 13 ppm due to anomalous land carbon uptake of 44 GtC (33–53), dominated by enhanced carbon storage in the Amazon under cooler and wetter conditions. In contrast, global ocean carbon storage decreases by 14 GtC, mainly north of 20°N, although carbon uptake increases in the northern North Atlantic. The AMOC-induced cooling breaks the near-linear relationship between cumulative CO2 emissions and warming, increasing the remaining carbon budget for limiting warming to 2°C by 63% (54–72). Compared to identical freshwater forcing under preindustrial conditions, the surface temperature, ocean heat content, and sea-level responses are substantially damped, indicating reduced climate sensitivity to AMOC collapse in a warmer world. These results demonstrate that a strong AMOC weakening would profoundly alter future climate–carbon cycle interactions and underscore the importance of explicitly accounting for AMOC risks in long-term climate assessments.
How to cite: Frölicher, T. L., Maier, P., Burger, F. A., Silvy, Y., Swingedouw, D., and Elizondo, U. H.: Climate and Carbon Cycle Responses to a 21st century AMOC collapse under a 2°C stabilization pathway, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22272, https://doi.org/10.5194/egusphere-egu26-22272, 2026.
Although the Atlantic Meridional Overturning Circulation (AMOC) is considered a critical climate tipping element, its impacts on the terrestrial carbon cycle in Earth system models remain uncertain. Using the Earth system model, CLIMBER-X, we investigate the response of vegetation carbon to idealized AMOC collapse under pre-industrial conditions. We assess the role of carbon-climate feedback by comparing simulations incorporating interactive carbon cycles with experimental results set at atmospheric CO₂ concentrations.
The results indicate that AMOC collapse leads to a large-scale change of vegetation carbon, with significant differences in responses between the Northern and Southern Hemispheres. The simulated global vegetation carbon response depends on whether the carbon-climate interaction is considered in the model, highlighting the importance of interactive carbon cycle processes. Our findings indicate the sensitivity of terrestrial vegetation carbon to AMOC changes and suggest that it is important to account for ocean-terrestrial-carbon coupling in Earth system models when assessing potential AMOC tipping events.
How to cite: Nian, D., Willeit, M., and Rockström, J.: Terrestrial Vegetation Carbon Responses to an AMOC Collapse in an Earth System Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14940, https://doi.org/10.5194/egusphere-egu26-14940, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) regulates large-scale heat and freshwater transport, and strongly influencing global climate patterns. Beyond its role in shaping mean climate conditions, the AMOC background state also modulates climate variability. The AMOC is a tipping element of the climate system and a collapse of the AMOC alters atmospheric circulation patterns such as the Hadley circulation, polar jet stream, and tropical trade winds, with consequences that extend far beyond the Atlantic basin. These changes affect atmospheric and oceanic variability, thereby reshaping global teleconnection patterns. Using the results of a full hysteresis simulation of the AMOC in the CMIP5 version of the Community Earth System Model (CESM), we study the importance of the present-day AMOC mean state in shaping the large-scale atmospheric circulation, the global oceanic circulation, and internal climate variability. By comparing equilibrium climate states under AMOC on- and off conditions, we investigate the role of the AMOC in climate variability phenomena, such as the El Niño-Southern Oscillation and the midlatitude patterns of sea surface temperature variability. Our results highlight the AMOC as a critical regulator of global climate variability, emphasising the importance of understanding its stability in a warming climate.
How to cite: Smolders, E., van Westen, R., and Dijkstra, H.: The Role of the AMOC in Shaping Internal Climate Variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11388, https://doi.org/10.5194/egusphere-egu26-11388, 2026.
The collapse of the Atlantic Meridional Overturning Circulation (AMOC) has long been classified as a low-probability, high-impact event. However, recent evidence suggests the probability of such a collapse may be significantly higher than previously estimated. From a disaster and risk management perspective, this shift calls for a re-evaluation of preparedness strategies and a deeper inquiry into how a drastic weakening or a complete shutdown would reshape the global risk landscape.
Central to these concerns is the role of AMOC in modulating Northern Hemisphere precipitation. An anthropogenic weakening could significantly alter future drought dynamics, further complicating the management of drought risk, a hazard already characterised by extensive socio-economic impacts.
To address these changing dynamics, we examine four sets of paired climate model simulations, each comparing a weakened AMOC state with a control run featuring a stable, stronger AMOC. Three of these experiment pairs employ the EC-EARTH3.3 model, where freshwater perturbations in the North Atlantic induce an artificial AMOC slowdown under fixed pre-industrial, present-day (2025), and future (2050, SSP5-8.5) forcing. The fourth pair employs the NASA GISS ModelE, simulating a spontaneous AMOC collapse under an extended SSP2-4.5 scenario without external freshwater forcing. Using an advanced Meteorological Drought Tracking approach based on the Standardized Precipitation Index (SPI) we quantify shifts in drought duration, severity, and spatial coherence, highlighting where significant changes would be expected.
How to cite: Volpi, D., Acosta Navarro, J. C., Bellucci, A., Caporaso, L., Corti, S., Fioravanti, G., Hrast Essenfelder, A., Meccia, V. L., Romanou, A., Toreti, A., and Zampieri, M.: Understanding Drought Risk in the Northern Hemisphere under AMOC weakening, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20190, https://doi.org/10.5194/egusphere-egu26-20190, 2026.
Previous studies indicate that cooling in the Subpolar North Atlantic (SPNA), known as the “Cold Blob,” may influence European summer heat extremes. However, how internally generated ocean–atmosphere variability and anthropogenic forcing jointly shape this relationship remains poorly understood. Here, we use the 50-member Max Planck Institute Grand Ensemble (MPI-GE) under the SSP2–4.5 scenario to assess how SPNA sea surface temperature (SST) anomalies affect the likelihood of exceptionally persistent European heatwaves.
We analyze ensemble-member differences in Atlantic Meridional Overturning Circulation (AMOC)–driven heat transport, SPNA SST evolution, and associated atmospheric circulation over Europe. We find that declining AMOC heat transport enhances ocean heat divergence in the subpolar gyre, promoting SPNA surface cooling and the emergence of the Cold Blob, although the magnitude and persistence of this cooling vary strongly across ensemble members. Persistent European heatwaves are favored primarily when subpolar cooling coexists with subtropical warming, strengthening the inter-gyre SST gradient and promoting stationary large-scale pressure systems over Europe. In mid-century projections, the relationship between cold SST anomalies and heatwaves is highly sensitive to the evolving oceanic background state.
Overall, our results demonstrate that internal coupled ocean–atmosphere variability strongly modulates near-term European summer heatwave risk under climate change and identify SPNA SSTs as a promising source of seasonal-to-multiyear predictability.
How to cite: Cerato, G., Lohmann, K., von Hardenberg, J., Bellomo, K., and Matei, D.: The Subpolar Gyre as Ocean–Atmosphere Bridge Between AMOC Variability and European Summer Temperature Extremes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14331, https://doi.org/10.5194/egusphere-egu26-14331, 2026.
This study performs uncertainty quantification on the regional mean surface temperature response to changes in the Atlantic Meridional Overturning Circulation (AMOC) and allows the investigation of novel AMOC scenarios. ESMs/GCMs primarily show gradual AMOC slowdown in the 21st and early 22nd century while other approaches suggest that a “tipping point” may be present which could lead to faster decline in the AMOC during this period. This study aims to estimate the impacts of a rapid decline or other AMOC scenarios and the range of possible outcomes which can be inferred from the current ensemble of climate models and approaches. Changes in temperature and AMOC will be analysed under a range of forcing scenarios including CMIP6 SSP scenarios for global warming, freshwater hosing scenarios from NAHosMIP, and ClimTip runs showing a combination of global warming and freshwater hosing. The relationships between AMOC change, global mean surface temperature and regional mean surface temperature are described, as well as our uncertainty in these values based on the model ensembles. These relationships are used to generate annual mean regional/ national temperature trajectories under a range of potential AMOC scenarios, with uncertainty ranges given for each scenario and location. These methods can be extended to both seasonal temperature and annual precipitation, and the data produced is highly consequential for economic impact assessments and adaptation planning.
How to cite: Rosser, J. and Stainforth, D.: Uncertainty Quantification of the regional temperature consequences of a large AMOC decrease and use in AMOC scenario exploration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8954, https://doi.org/10.5194/egusphere-egu26-8954, 2026.
We identify a millennial-scale oscillatory eigenmode of the Atlantic Meridional Overturning Circulation (AMOC) in a conceptual two-hemisphere box model. To isolate the governing mechanism, we examine two idealized cases that represent situations where AMOC variability arises exclusively from the North Atlantic Deep Water (NADW) cell or from the Antarctic Bottom Water (AABW) cell.
In the NADW-influenced case, the AMOC anomaly is parameterized as positively related to the north-south salinity difference. Linear analysis shows that the oscillation period increases as the mean AMOC strength decreases. Thus, a weaker mean AMOC produces slower oscillations, and the dominant time scale can shift from multicentennial to millennial. For example, when the mean AMOC strength is near 10 Sv, the model yields a dominant millennial-scale oscillation.
In the AABW-influenced case, the AMOC anomaly arises from AABW-related processes and exhibits a negative linear dependence on the north-south salinity difference. The resulting millennial oscillation is driven by upward transport from the deep to the upper South Atlantic, a process that responds sensitively to local surface freshwater fluxes.
Taken together, these results highlight internal ocean dynamics that can generate millennial-scale AMOC variability through two distinct pathways, associated with northern and southern overturning processes, respectively. Finally, we discuss the implications of these findings for interpreting observed millennial-scale climate variability during the last glacial period and the Holocene.
How to cite: Zhou, X. and Yang, H.: Millennial-Scale Oscillation of the AMOC in a Two-hemisphere Box Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10253, https://doi.org/10.5194/egusphere-egu26-10253, 2026.
A potential Atlantic Meridional Overturning Circulation (AMOC) slowdown, possibly caused by external forcings, is widely debated, and its historical drivers and future evolution remain uncertain. Here we disentangle the effects of greenhouse gases and anthropogenic aerosols on the AMOC and on other relevant processes in the high-latitude North Atlantic (NA) over 1850–2014. We analyze a multi-model ensemble of experiments from the Large Ensemble Single Forcing Model Intercomparison Project, specifically: hist-GHG (varying concentrations of greenhouse gases, other forcings constant) and hist-aer (same as hist-GHG, but for anthropogenic aerosols), and we compare these to the respective CMIP6 historical simulations (all forcings varying) and observational datasets.
Robust AMOC weakening under hist-GHG and strengthening under hist-aer is found across the respective multi-model ensembles with various accompanying changes, exhibiting a high degree of spatial antisymmetry. In both sets of experiments, the same causal pathway (yet with opposite sign) occurs. We describe the key role of subpolar upper-ocean salinity and connect its variations to changes in sea ice and air–sea heat fluxes. Our results indicate that the primitive radiative forcing directly impacts sea-ice mass, and thereby drives upper-ocean salinity variations, while accompanying changes in surface freshwater fluxes further modulate salinity. The resulting variations in salinity induce changes in upper-ocean density and stratification in the subpolar NA that, in turn, determine the simulated AMOC trends. We further discuss key mechanisms in play, including the positive AMOC–salinity and AMOC–evaporation feedbacks, describing the dominant processes of the causal pathway.
By offering insights onto the respective roles of external forcings in the context of climate change and by advancing our understanding of key NA ocean–atmosphere interactions, our results also highlight models limitations in the representation of coupled processes that are critical for reliable projections.
How to cite: Giaquinto, D., Nicolì, D., Smith, D. M., Iovino, D., Frierson, D., and Athanasiadis, P. J.: Understanding AMOC changes resulting from varying historical radiative forcings, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17467, https://doi.org/10.5194/egusphere-egu26-17467, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the climate system with far-reaching effects on global climate. Here, we investigate the influence of ocean basins beyond the Atlantic on both AMOC dynamics and surface climate variability, using simulations with the coupled climate model MPI-ESM-LR. We apply an AMOC upwelling pathways framework to quantify the influence of the Indo-Pacific and Southern Ocean on AMOC strength over the 58-year time period 1958-2014 in three model setups: a historical simulation, an atmosphere-only assimilation, and a coupled atmosphere-ocean assimilation. Through regression analysis, we reveal the relationship between the AMOC upwelling pathways in the different ocean basins and sea-surface temperature (SST). Preliminary results show distinct SST patterns on a global scale for each setup, suggesting teleconnections between the AMOC and its upwelling components, and global surface climate dynamics. By comparing the different model setups, we assess the impact of the assimilation of observational data on the representation of the AMOC, the SST and their relationship, and improve our understanding of the role of the AMOC as part of the global climate system.
How to cite: Bühl, T., Brune, S., and Baehr, J.: An analysis of the imprint of the global ocean circulation on AMOC dynamics and surface climate during the time period 1958-2014, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3811, https://doi.org/10.5194/egusphere-egu26-3811, 2026.
The strength and variability of the Atlantic Meridional Overturning Circulation (AMOC) are closely linked to deep water formation (DWF) in three key regions: the Labrador Sea, the Irminger Sea, and the Greenland Sea. However, quantifying the relative contributions of these regions to the AMOC in climate models and how these contributions evolve under future climate scenarios remains challenging. While CMIP6 models consistently project a weakening of the AMOC, they show wide inter-model spread in the rate of decline. This highlights the need for robust metrics that enable more informative intercomparison. The commonly used mixed layer depth metric captures some aspects of convection, but does not directly quantify DWF. Here, we introduce a volume-conservation-based diagnostic that serves as an index for quantifying DWF, enabling robust comparison across models with differing resolution and complexity. It further quantifies the regional contributions of the Labrador, Irminger and Greenland Seas to the AMOC.
When applied to EC-Earth3 at standard and high resolutions, the diagnostic suggests that DWF in the Labrador Sea is the main cause of the projected weakening of the AMOC. Meanwhile, the Irminger Sea emerges as the AMOC's largest overall contributor, experiencing only a modest decline and remaining essential for sustaining the circulation. At the same time, the contribution from the Arctic increases. We assess inter-model differences in DWF magnitude and examine their relationship to AMOC changes by extending the analysis to a suite of CMIP6 models. This allows us to evaluate the robustness of these processes across models. Overall, our results provide new insight into the factors underlying differences in AMOC projections among models and into the mechanisms that may influence the risk of an AMOC slowdown or tipping point.
How to cite: Karami, M. P., Navarro-Labastida, R., Koenigk, T., and Chafik, L.: A diagnostic framework for deep water formation and AMOC variability in selected CMIP6 models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20496, https://doi.org/10.5194/egusphere-egu26-20496, 2026.
Statistical methods generally predict a possible tipping of the Atlantic Meridional Overturning Circulation (AMOC) in the near future, suggesting that the climate models overestimate the stability of AMOC. Conversely, observations show a stable AMOC during the past decades, suggesting otherwise. Based on the MITgcm-ECCO2, here we show that the biases in the simulated Arctic sea ice, freshwater content, and the water transport across various straits/passages around the Arctic play a key role in the future stability of AMOC in the climate models. Specifically, most climate models project an increased freshwater export from the Arctic across the Fram Strait in the future. In contrast, our model, with minimal bias for the present day, simulates a decrease in freshwater export across the Fram Strait but an increase across the Lancaster Strait. This shift of location increases AMOC stability as the freshwater coming out of Fram Strait has a direct impact on the surface density over the North Atlantic deepwater formation region.
How to cite: Gavilan Pascual-Ahuir, E. and Liu, Y.: A Resilient Atlantic Meridional Overturning Circulation in the Near Future, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14045, https://doi.org/10.5194/egusphere-egu26-14045, 2026.
It has been shown that predictability of the North Atlantic Oscillation (NAO) in seasonal forecasts is better than models suggest, a consequence of the signal-to-noise paradox, whereby individual ensemble members contain a smaller proportion of the predictable variance than seen in observations. We intend to use two seasonal forecast models, GloSea6 and CESM-SMYLE, to study whether ‘NAO-matching’, where we select only the ensemble members that most closely resemble the ensemble mean NAO, can produce more accurate seasonal forecasts of the Atlantic Meridional Overturning Circulation (AMOC) than the full seasonal forecast ensemble. This method has been shown to improve predictability of other aspects of the North Atlantic climate, such as the Atlantic Multidecadal Variability pattern and Northern European Precipitation. The skill of AMOC predictability in seasonal hindcasts will be assessed against the RAPID array observations as well as historical reconstructions of the overturning circulation to determine whether it too is subject to signal-to-noise errors, and consequently if ‘AMOC-matching’ is a potentially useful calibration tool for improving predictability of its related climate impacts.
How to cite: Hay, S., Walsh, A., Screen, J., Scaife, A., and Robson, J.: Leveraging the signal-to-noise paradox to improve seasonal forecasts of the AMOC and its impacts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21430, https://doi.org/10.5194/egusphere-egu26-21430, 2026.
For climate predictions on decadal to multi-decadal time scales, the ocean circulation has been found to carry a substantial portion of the memory from initialisations. In this study, we analyse the global ocean overturning circulation, in particular the Atlantic meridional overturning circulation (AMOC), in climate simulations with the global coupled model MPI-ESM for the time period 1960-2100. We compare an ensemble of multi-decadal predictions, initialised from a coupled assimilation simulation, and an ensemble of uninitialised simulations, both with CMIP6 historical and SSP2-45 external forcing. We find three distinct time scales for the evolution of the AMOC strength at 26N after the initialisation time. On a time scale up to 5 years after initialisation, the AMOC reacts to the initialised state with a rapid under- or overshooting when compared to uninitialised simulations, depending on the initialisation time. On a time scale of 30 to 140 years after initialisation, the AMOC by and large maintains this bias between initialised predictions and uninitialised simulations. We also find these distinct time scales in the characteristics of the AMOC cells, in both the overturning and re-circulation cells. In addition, we show that the AMOC evolution is related to the global ocean circulation. Specifically, we find a strong connection of the AMOC cell with the global Southern Ocean circulation, and we also find that multi-decadal AMOC trends are being partly compensated by changes in the strength of the Indo-Pacific meridional overturning. Our results show that the ocean circulation, in particular the AMOC, may carry the information about initialisation over multi-decadal time scales, up to 140 years. While this does not necessarily imply good prediction skill on the multi-decadal time scale, it adds another dimension on how we asses the uncertainty of climate projections until 2100.
How to cite: Brune, S., Hansen, J., Bühl, T., Uddin, M. B., Düsterhus, A., and Baehr, J.: The Atlantic meridional overturning circulation in multi-decadal end of century climate predictions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5291, https://doi.org/10.5194/egusphere-egu26-5291, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) is a tipping element of the climate system, capable of transitioning from a strong overturning state to a substantially weaker one. AMOC collapse can occur through the destabilising salt-advection feedback, which may be triggered by freshwater input into the North Atlantic Ocean. Alternatively, the AMOC may become unstable under 21st century climate change. This risk was recently reassessed in the Global Tipping Points Report (2025), which suggests that the AMOC could become unstable above 1.5°C of global warming. By contrast, other studies report stable AMOC states even under extreme climate change conditions (e.g., 4xCO2). Consequently, it remains unclear whether a global warming threshold for AMOC tipping exists.
Here, we analyse transient CO2 forcing experiments performed with the Community Earth System Model (CESM) at different rates of CO2 increase. For slow ramping (+0.5 ppm yr-1), we show that the AMOC remains stable under extreme climate change, up to +5.5°C of global warming. In contrast, under more rapid forcing in the RCP4.5 and RCP8.5 scenarios, the AMOC collapses at much lower warming levels of +2.2°C and +2.8°C, respectively. These results demonstrate that AMOC tipping is strongly radiative path-dependent rather than governed by a specific global temperature threshold. Slow forcing permits a coherent adjustment of surface and interior ocean properties, supported by enhanced evaporation and reduced sea-ice extent, which together stabilise the AMOC. A similar stabilising response is found in several CMIP6 models under extended SSP scenarios. Our findings imply that limiting the rate of radiative forcing increase is crucial for reducing the near-term risk of AMOC collapse and other climate tipping elements.
How to cite: van Westen, R., Börner, R., and Dijkstra, H.: Radiative Forcing Path Dependent Temperature Thresholds for AMOC Tipping, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9875, https://doi.org/10.5194/egusphere-egu26-9875, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) is weakening in response to global warming, while Nordic Seas Overturning Circulation (NOC) is projected to increase. So far, no causal link has been proposed between these two opposing trends. Here we propose that a density reduction in the subpolar North Atlantic will weaken the AMOC by reducing the density difference with lighter waters further south, while at the same time strengthening the NOC by increasing the density difference with the heavier waters further north. Using high resolution climate model data and a box model, we find that in response to combined global warming and freshwater input the NOC initially increases moderately as the AMOC weakens, while a tipping point may be reached later if deep convection in the Nordic Seas shuts down and the NOC collapses together with the AMOC.
How to cite: Roewer, S., Fiedler, L., Årthun, M., Huiskamp, W., and Rahmstorf, S.: Nordic Overturning Increases as AMOC Weakens in Response to Global Warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5641, https://doi.org/10.5194/egusphere-egu26-5641, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) plays a central role in regulating Earth's climate, and is widely considered to be a vulnerable tipping element of the climate system. The Bering Strait Throughflow (BST) can play a key role in the AMOC's stability. Through this narrow passage relatively fresh Antarctic Intermediate Water from the Pacific basin enters the Arctic Ocean and eventually ends up in the deep-water formation zones in the North Atlantic. Moreover, an open Strait enhances the freshwater exchange between the Arctic and North Atlantic. All in all, the Throughflow's net effect is a freshening of the North Atlantic, and hence a weakening of the AMOC. Recent research has indicated that the AMOC is weakening and may reach its tipping point before the end of this century. Since the Bering Strait has limited width and is relatively shallow (approximately 80 km across and on average 50 m deep) constructing a barrier is technically feasible. In this work we show that such a barrier can prevent an AMOC collapse in three levels of the model hierarchy. Firstly, a conceptual model of the World Ocean is extended to include the BST and Arctic amplification, showing that for a low freshwater forcing in the North Atlantic a closure of the Strait prevents an AMOC tipping under climate forcing. Moreover, the conceptual framework allows us to test the sensitivity of the results with respect to BST parametrization and rate of forcing. Next, the conceptual results are reproduced in an Earth system Model of Intermediate Complexity (EMIC). Here we have investigated the AMOC's safe carbon budget for either an open or closed Strait for various freshwater hosing strengths. This reveals an increased carbon budget under a closure given -again- a sufficiently low strength of North Atlantic hosing. Lastly, the closure's effectiveness is tested in a CMIP5 model, namely CESM1. Here an AMOC collapse occurs under RCP8.5 forcing for both a low and high freshwater hosing. In the former the AMOC strength matches observations, while in the latter the overturning-induced freshwater transport through the Atlantic's southern boundary is realistic. In both scenarios a closure of the Bering Strait prevents an AMOC collapse on the condition that this closure occurs sufficiently early. In the strong hosing scenario a closure has to occur at least as early as 2050, while in the low hosing case a closure as late as 2080 is still sufficient. Hence, we have shown throughout the model hierarchy that a closure of the Bering Strait can prevent a collapse of the AMOC, and that it is a potential climate intervention strategy should emissions mitigation fail.
How to cite: Soons, J., van Westen, R., and Dijkstra, H. A.: A Constructed Closure of the Bering Strait to prevent an AMOC tipping, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10492, https://doi.org/10.5194/egusphere-egu26-10492, 2026.
Paleoclimate evidences and coupled model studies suggested that the Atlantic Meridional Overturning Circulation(AMOC) has significant multicentennial variability. In this study, we use simplified two-dimensional and three-dimensional ocean model to extend previous theoretical and coupled model studies on the multicentennial oscillation(MCO) of AMOC, providing clearer physical insights and bridging the gap between idealized conceptual model and high-complexity numerical models. Our results demonstrate that stochastic salinity forcing effectively excites AMOC MCO, with the oscillation primarily driven by the tropical-subpolar advection feedback. Sensitivity experiments show that the period of the AMOC MCO is largely determined by the strength and vertical structure of the climatological AMOC: a stronger AMOC leads to a shorter oscillation period, while a deeper AMOC maximum results in a longer period. Under weak AMOC conditions, the oscillation timescale can extend to millennial scales. We also explore the role of wind-driven circulation and find that, although it has little influence on the MCO period, it slightly modifies the amplitude of variability by suppressing low-frequency components and enhancing high-frequency fluctuations. These simplified ocean model enables a systematic exploration of key physical mechanisms underlying AMOC MCO, offering valuable insights into long-term climate variability.
How to cite: Wang, S., Yang, H., and Zhou, X.: Investigating the multicentennial oscillation of the AMOC using simplified ocean model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10948, https://doi.org/10.5194/egusphere-egu26-10948, 2026.
This project aimed to investigate how southern Australia was impacted by the AMOC driven millennial scale climate events of the Last Glacial Period.
Paleoclimate studies have demonstrated that abrupt millennial-scale climate events during the Last Glacial Period coincided with variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC). These include Dansgaard-Oeschger events, which coincide with periods of AMOC strengthening, and Heinrich events, which coincide with AMOC weakening or collapse.
Whilst numerous paleoclimatic studies have examined the global climatic and environmental consequences of these events, relatively few of these studies are based in the southern hemisphere, even fewer in Australia, with southern Australia largely overlooked. This is a problem, as there is currently very little understanding of how the southern Australian hydroclimate, fire regimes and vegetation was impacted by AMOC slowdown and/or shutdown in the past. Moreover, the scarcity of high resolution, temporally extensive paleoclimatic records in southern Australia constrains our capacity to understand interhemispheric leads & lags as well as the local response to rapid climate events.
To address these knowledge gaps, this project produced three new southern hemisphere mid-latitude paleoclimatic datasets and improved the age-constraints and proxy resolution on one existing published paleoclimatic dataset.
Three speleothems were analysed for this project- from Mammoth Cave (Southwest Western Australia), Kubla Khan Cave (Tasmania, Australia) and Hollywood Cave (South Island, New Zealand). We investigated the paleohydrology of these sites using stable isotope analysis (δ¹⁸O and δ¹³C), trace element analysis and geochronology (U-Th dating). The datasets from Mammoth Cave (38-14ka) and Kubla Khan (75-23 ka) have demonstrated hydroclimate excursions associated with millennial climate events, likely due to the meridional displacement of the South Westerly Winds. Extensive U/Th dating of the Hollywood Cave speleothem (73-11ka) has altered the pre-existing, published age model, with implications for the current interpretation of millennial climate event timing in the southern mid-latitudes.
A lake sediment sequence was also analysed as part of this project, to determine the vegetation, fire regime and hydroclimate impacts of AMOC driven millennial climate events. Lake Bullen Merri (western Victoria) was cored in early 2025, yielding 15m of lake sediment and ~36,000 years of climate history. Thirty-one 14C dates have been returned, providing a robust age-depth model. A suite of analyses have been applied to this sediment core; X-RF, magnetic susceptibility, loss on ignition, palynology, macroscopic and microscopic charcoal counting, biomarkers (n-alkanes, sterols, PAH’s) and leaf wax H-Isotope analysis. These results show significant hydroclimate & fire activity excursions throughout the past ~36,000 years, with higher resolution proxy analysis underway to highlight millennial/centennial scale excursions.
These results provide one of the first insights into the way southern Australia is impacted by millennial scale climate events, offering a valuable regional insight, as well as a point of comparison for interhemispheric studies.
How to cite: Sheridan, L., Fletcher, M.-S., Drysdale, R., and Korasidis, V.: Investigating the impact of millennial scale climate events on southern Australia during the Last Glacial Period, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17273, https://doi.org/10.5194/egusphere-egu26-17273, 2026.
Atmospheric heat and carbon uptake and storage by the ocean are controlled by seawater stratification, which is also linked to Atlantic Meridional Overturning Circulation (AMOC) through ocean heat distribution that can modify density stratification. The effects of a potential weakening of the AMOC on ocean stratification, and therefore on heat uptake and storage, remain an open question. To gain insight into these dynamics, we used marine sedimentary archives of the last deglaciation (last 27000 years) to reconstruct temperatures at intermediate (GeoB9512-5, 793 m water depth) and deep (GeoB9508-5) water masses of the eastern Atlantic off the coast of Senegal (northwestern Africa). During this time, marked changes in AMOC strength took place: the Last Glacial Maximum (LGM, 23,000 – 19,000 years ago), a time of shallower meridional overturning; and the Heinrich Stadial 1 (HS1, 18,200–14,900 years ago) and Younger Dryas (YD, 12,800–11,700 years ago), when AMOC was weaker than today. Our benthic foraminifera-based Mg/Ca (seawater temperature) and δ18O (ocean density) show that a persistently shallow and strong (LGM) or weak (HS1 and YD) meridional overturning led to a mid-depth warming at the same time deep-ocean heat uptake was paused, leading to a strong density stratification in the Atlantic. These results are compatible with previous temperature reconstruction across the tropical and north Atlantic, and also show that with a Holocene AMOC strengthening, mid-depth cooling and resumed deep-ocean heat uptake resulted in a weaker stratification. Our findings show that the AMOC state sets the depth of heat storage and that the depth of the upper AMOC cell is tightly related to deep ocean stratification.
How to cite: Barragán Montilla, S., Mulitza, S., Johnstone, H. J. H., and Pälike, H.: Deglacial ocean density de-stratification with a weaker Atlantic Meridional Overturning Circulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1299, https://doi.org/10.5194/egusphere-egu26-1299, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) has shown signs of decline over the last two decades. Climate models project that a continued slowdown of the AMOC will increase precipitation over parts of northern Europe, particularly in the Irish-British Isles1, with potential impacts on agriculture and related systems. However, the ability of climate models to predict when such changes might occur remains limited, calling for the use of paleoclimate archives. Here, we present a stalagmite‑based paleoclimate record from the west coast of Ireland spanning 11.1–7.7 ka (b2k). Combined Sr/Ca and stable isotope data indicate a sudden increase in precipitation at ~8.6 ka, coincident with the collapse of the Hudson Bay Ice Saddle (HBIS)2 and a reduction in eastern North Atlantic bottom and surface currents3,4. We interpret this hydroclimatic shift as a response to the slowdown of the AMOC caused by the HBIS freshwater discharge, indicating a minimum time lag (of decadal scale) between ocean circulation disruption and atmospheric response. Due to enhanced thermal and pressure gradients over the North Atlantic, a weakened AMOC can favour positive North Atlantic Oscillation (NAO+) conditions, which typically bring wetter and stormier weather over northern Europe. We therefore associate the ~8.6 ka precipitation increase with the development of NAO+ conditions in the region, which aligns with existing work5. In addition, our record evidences sustained precipitation throughout the '8.2 ka' cooling anomaly, suggesting that, regardless of temperature direction, heightened precipitation is a persistent consequence of AMOC reduction in northwest Europe.
1: Jackson et al. (2015) Climate Dynamics, 45. 2: Lochte et al. (2019) Nature Communications, 10, 586. 3: Ellison et al. (2006) Science, 312. 4: Thornalley et al. (2009) Nature, 457. 5: Smith et al. (2016) Scientific Reports, 6, 24745.
How to cite: Ansberque, C., Schenk, F., Mark, C., Hällberg, P., Kylander, M., and McDermott, F.: Rapid climatic response to the Hudson Bay Ice Saddle collapse (~8.6 ka) recorded in Ireland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7116, https://doi.org/10.5194/egusphere-egu26-7116, 2026.
Under greenhouse gas forcing, the global climate exhibits a long-term warming trend superimposed with quasi-periodic multidecadal oscillations (~60–70 years) closely linked to the Atlantic Meridional Overturning Circulation (AMOC). As a pivotal component of global ocean circulation, the AMOC regulates the distribution of oceanic heat and freshwater, exerting profound influence on global climate variability. Conventional views posit a positive correlation between AMOC strength and global mean surface temperature (GMST) on multidecadal timescale. However, our analysis reveals a significant phase shift of approximately 45°–90° between AMOC and GMST on multidecadal timescale under anthropogenic warming. This shift arises as enhanced vertical ocean heat transport within the subpolar North Atlantic’s mid-depth layers modulates the surface energy budget balance under increasing radiative forcing, thereby disrupting the equilibrium between horizontal meridional heat transport and surface net heat flux. External radiative forcing perturbs internal climate variability, driving a substantial reduction in mean-state density in the subpolar North Atlantic’s mid-depth ocean. Crucially, the intensified vertical heat transport associated with AMOC strengthening emerges as the key mechanism facilitating heat sequestration into the ocean interior.
How to cite: Bi, H., Chen, X., Li, X., and Tung, K.-K.: Phase Shift of AMOC and Multidecadal Global Mean Surface Temperature Under Anthropogenic Forcing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-603, https://doi.org/10.5194/egusphere-egu26-603, 2026.
The Atlantic Meridional Overturning Circulation (AMOC) is a key regulator of global climate and has been a subject of major scientific interest. Observational studies have raised concerns about its ongoing weakening and potential collapse this century. While climate models generally show an overall cooling over Europe as a result of this weakening, confirmation based on observations is lacking due to difficulties in assessing causality in data. Here, we overcome this problem by constructing causality maps and tracking AMOC’s impact over Europe in observations. First, the causal link between AMOC and its SST fingerprint is established. Then, decomposing the SST fingerprint of AMOC into a decreasing centennial trend and a multidecadal oscillation (AMO), we find the trend impacts only winter and AMO only summer. In winter, the weakening warms north-central Europe and increases northern precipitation, with no overall cooling being observed nor expected. In summer, AMO induces multidecadal oscillations in temperature and precipitation. These quantitative results can be an observational benchmark for future model simulations, inform policy making, and national security.
How to cite: Nichita, D., Dima, M., Vaideanu, P., and Ionita, M.: A weakened AMOC warms winters and drives summer multidecadal variability over Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1849, https://doi.org/10.5194/egusphere-egu26-1849, 2026.
Cooling across Europe is the most widely mentioned impact of a weakened AMOC. However, we find that the end-of-century net temperature change over Europe, including both the AMOC-induced cooling and global warming, remains surprisingly undetermined in the existing literature. In our study, using both new Earth system model simulations and existing multi-model evidence, we show that certain parts of Europe could cool below preindustrial temperatures in scenarios with both a substantial AMOC weakening and low emissions. Under continued emissions, however, most regions would either not face the risk of net cooling or only at very high amounts of AMOC weakening. Simulations under combined scenarios of AMOC weakening and global warming reveal that the effect of a given amount of AMOC weakening on European temperatures is remarkably linear and independent of the underlying emissions scenario. This relationship circumvents the large uncertainties around the AMOC’s future evolution by instead inferring the amount of AMOC weakening that would cool a specific European region or country for any global warming scenario.
How to cite: Alastrué de Asenjo, E. and Schaumann, F.: Could Europe actually cool if the AMOC weakens in a warming climate?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11518, https://doi.org/10.5194/egusphere-egu26-11518, 2026.
The projected weakening of the Atlantic Meridional Overturning Circulation (AMOC) poses substantial risks for global and regional climate stability. While the large-scale cooling associated with a weakened AMOC is well-documented, how weather and climate extremes respond to such changes remains little examined. Here, we investigate how recent European summer and winter temperature extremes (2018-2022) would change under different weakened AMOC states using the Alfred Wegener Institute Climate Model (AWI-CM3). We generate three sets of five-member ensemble simulations, each representing a different AMOC state: a factual (present-day AMOC) state and two counterfactual states with a weakened and a shut-down AMOC. All simulations are spectrally nudged to the large-scale winds observed during 2017-2022. We thus focus primarily on the thermodynamic impacts induced by AMOC weakening within the same realization of atmospheric variability. Our research indicates that a weakened AMOC generally reduces the occurrence of summer hot days, though this response is spatially heterogeneous, implying a flow-dependence of the AMOC-related impact. For instance, Eastern Europe remains comparatively less affected even when AMOC strength is reduced by 60% relative to the present day conditions. In contrast, winter cold extremes are substantially intensified. We observe a drastic increase in cold days, with daily minimum temperatures during these events decreasing by more than 6 °C in several northwestern European capital cities. These findings highlight the nonlinear and seasonally asymmetric responses of European temperature extremes to AMOC weakening and provide important insights for regional climate risk assessment and adaptation strategies.
How to cite: Ma, Q., Athanase, M., Sanchez-Benitez, A., Streffing, J., Goessling, H., Jung, T., Lohmann, G., and Ionita, M.: Response of European Temperature Extremes to a Weakened AMOC, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12946, https://doi.org/10.5194/egusphere-egu26-12946, 2026.
A weakening of the Atlantic Meridional Overturning Circulation (AMOC) is often portrayed as economically beneficial - leading to a reduction in the social cost of carbon. The reduced social cost of carbon is attributed to the reduction of temperatures in large parts of the globe. However, the existing literature relies on integrated assessment models (IAMs) without an explicit representation of AMOC strength, and is therefore unable to consider the implicit AMOC weakening that is already included in projected temperature patterns. This study accounts for the amount of AMOC weakening that is implicit in pattern scaling procedures within the IAM when considering the effects of AMOC weakening. The implicit AMOC weakening is teased out from the pattern scaling as a function of global mean temperature change across CMIP6 models. Additionally, we recalibrate the temperature response to AMOC weakening at the country level by analysing simulations from the North Atlantic Hosing Model Intercomparison Project (NAHosMIP). The new temperature response, as well as four already implemented responses, are considered using the META IAM. We then analyse the change in social cost of carbon caused by AMOC weakening along seven different AMOC projections, taking into account the AMOC response implicit in pattern scaling. Overall, we find that AMOC weakening-induced temperature changes lower the social cost of carbon. Contrary to previous assumptions, this reduction in the social cost of carbon is driven only by global mean cooling, whereas the pattern of the temperature responses increases the social cost of carbon.
How to cite: Hansen, J., Alastrué de Asenjo, E., Schaumann, F., and Baehr, J.: Assessing the effect of AMOC-induced temperature patterns on the global social cost of carbon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18114, https://doi.org/10.5194/egusphere-egu26-18114, 2026.
