Observational constraints project a~50% AMOC weakening by the end of this century.

Abstract. By regulating the global transport of heat, freshwater, and carbon, the Atlantic meridional overturning circulation (AMOC) serves as an important component of the climate system. During the late 20th and early 21st centuries, indirect observations and models suggest a weakening of the AMOC. Direct AMOC observations also suggest a weakening during the early 21st century but with substantial interannual variability. Long-term weakening of the AMOC has been associated with increasing greenhouse gases (GHGs), but some modeling studies suggest the build up of anthropogenic aerosols (AAs) may have offset part of the GHG-induced weakening. Here, we quantify 1900–2020 AMOC variations and assess the driving mechanisms in state-of-the-art climate models from the Coupled Model Intercomparison Project phase 6 (CMIP6). The CMIP6 forcing (GHGs, anthropogenic and volcanic aerosols, solar variability, and land use and land change) multi-model mean shows negligible AMOC changes up to ∼ 1950, followed by robust AMOC strengthening during the second half of the 20th century (∼ 1950–1990) and weakening afterwards (1990–2020). These multi-decadal AMOC variations are related to changes in North Atlantic atmospheric circulation, including an altered sea level pressure gradient, storm track activity, surface winds, and heat fluxes, which drive changes in the subpolar North Atlantic surface density flux. To further investigate these AMOC relationships, we perform a regression analysis and decompose these North Atlantic climate responses into an anthropogenic aerosol-forced component and a subsequent AMOC-related feedback. Similar to previous studies, CMIP6 GHG simulations yield robust AMOC weakening, particularly during the second half of the 20th century. Changes in natural forcings, including solar variability and volcanic aerosols, yield negligible AMOC changes. In contrast, CMIP6 AA simulations yield robust AMOC strengthening (weakening) in response to increasing (decreasing) anthropogenic aerosols. Moreover, the CMIP6 all-forcing AMOC variations and atmospheric circulation responses also occur in the CMIP6 AA simulations, which suggests these are largely driven by changes in anthropogenic aerosol emissions. More specifically, our results suggest that AMOC multi-decadal variability is initiated by North Atlantic aerosol optical thickness perturbations to net surface shortwave radiation and sea surface temperature (and hence sea surface density), which in turn affect sea level pressure gradient and surface wind and – via latent and sensible heat fluxes – sea surface density flux through its thermal component. AMOC-related feedbacks act to reinforce this aerosol-forced AMOC response, largely due to changes in sea surface salinity (and hence sea surface density), with temperature-related (and cloud-related) feedbacks acting to mute the initial response. Although aspects of the CMIP6 all-forcing multi-model mean response resembles observations, notable differences exist. This includes CMIP6 AMOC strengthening from ∼ 1950 to 1990, when the indirect estimates suggest AMOC weakening. The CMIP6 multi-model mean also underestimates the observed increase in North Atlantic ocean heat content, and although the CMIP6 North Atlantic atmospheric circulation responses – particularly the overall patterns – are similar to observations, the simulated responses are weaker than those observed, implying they are only partially externally forced. The possible causes of these differences include internal climate variability, observational uncertainties, and model shortcomings, including excessive aerosol forcing. A handful of CMIP6 realizations yield AMOC evolution since 1900 similar to the indirect observations, implying the inferred AMOC weakening from 1950 to 1990 (and even from 1930 to 1990) may have a significant contribution from internal (i.e., unforced) climate variability. Nonetheless, CMIP6 models yield robust, externally forced AMOC changes, the bulk of which are due to anthropogenic aerosols.

Abstract. The Coupled Model Intercomparison Project (CMIP) allows the assessment of the representation of the Atlantic Meridional Overturning Circulation (AMOC) in climate models. While CMIP Phase 6 models display a large spread in AMOC strength, the multi-model mean strength agrees reasonably well with observed estimates from RAPID1, but this does not hold for the AMOC's various components. In CMIP Phase 6 (CMIP6), the present-day AMOC is characterized by a lack of lower North Atlantic Deep Water (lNADW) due to the small scale of Greenland–Iceland–Scotland Ridge overflow and too much mixing. This is compensated for by increased recirculation in the subtropical gyre and more Antarctic Bottom Water (AABW). Deep-water circulation is dominated by a distinct deep western boundary current (DWBC) with minor interior recirculation compared with observations. The future decline in the AMOC of 7 Sv by 2100 under a Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5) emission scenario is associated with decreased northward western boundary current transport in combination with reduced southward flow of upper North Atlantic Deep Water (uNADW). In CMIP6, wind stress curl decreases with time by 14 % so that wind-driven thermocline recirculation in the subtropical gyre is reduced by 4 Sv (17 %) by 2100. The reduction in western boundary current transport of 11 Sv is more than the decrease in wind-driven gyre transport, indicating a decrease over time in the component of the Gulf Stream originating from the South Atlantic.

 Understanding the stability of the Atlantic Meridional Overturning Circulation (AMOC) and its future development under anthropogenic forcing is of key importance for advancing climate science. Previous studies have explored the stability of the AMOC by applying external perturbations in climate models, such as freshwater hosing to the North Atlantic Ocean. However, if the system is close to losing stability, the tipping of the AMOC may also spontaneously occur via internal coupled atmosphere-ocean variability. Here, we address this hypothesis - using an innovative approach - by studying the nature of a spontaneous collapse of the AMOC in an intermediate complexity climate model (PlaSIM coupled to the LSG ocean) featuring - under pre-industrial conditions - an apparently stable state. Excluding all possible external forcing elements (for example green-house gasses increase, water hosing, radiative forcing anomalies), significant AMOC slowdowns and collapses can be treated as extreme events solely driven by the chaotic internal atmospheric variability.  Facing this problem, we look for extreme AMOC slowdowns by applying a Rare Event Algorithm (Ragone, Wouters and Bouchet, 2018), which - via a selective cloning of the most interesting model trajectories -  allows a faster exploration of the model phase space in the direction of an AMOC decrease.After exploring the parameters of the rare event algorithm, we find a regime in which PLASIM/LSG shows an abrupt AMOC slowdown over a 20-years period to a substantially weakened state, which is unprecedented in the pre-industrial run. Stability analysis reveals that part of these slowdown states are actually collapsed, i.e. states around a much lower value of the AMOC that do not recover to previous values.This approach also enables us to isolate the atmospheric processes driving the AMOC slowdown, from the climate response to the weakened AMOC state. Interestingly, we find that the climatic response to internally-induced AMOC slowdowns shows strong similarities with the responses to externally forced AMOC slowdowns in state-of-the-art climate models  for what concerns temperature, wind, and precipitation changes. Looking at the mechanisms causing the AMOC weakening, instead, we find that zonal wind stress over the North Atlantic is the main driver of the AMOC slowdown, via changes in Ekman transport that affect salinity and deep convection in the Labrador sea. In this climate model, the repeated occurrence of this circulation anomaly for a few decades is sufficient to drive  an AMOC collapse without possibility of recovery on multi-centennial time scales.Overall, these results show that the methodology proposed here can be generally useful for other studies in Tipping Points since it introduces the possibility of collecting a large number of critical events that cannot be sampled using traditional approaches.  

The recent Environmental Research Letters article by Caesar, Rahmstorf and Feulner (hereafter CRF) is essentially a Comment on our Nature paper (Chen and Tung 2018 Nature 559 387–91), but without an accompanying rebuttal from us. In this unusual format for the exchange outside Nature, our rebuttal then becomes a Comment here at Environmental Research Letters. Our original proposal that the rate of global warming is enhanced by a weak Atlantic Meridional Overturning Circulation (AMOC) remains valid and is strengthened with this exchange. CRF used “established evidence” to argue against our finding, but such evidence is either misapplied (i.e. applying model results from preindustrial control runs with constant greenhouse gasses to the industrial era with increasing greenhouse gasses), or misinterpreted (i.e. climate model results for the industrial era specifically for the trends interpreted as for the AMOC cycles). While we used the observed energy budget to show that a strong (weak) AMOC transports more (less) heat to below 200 m, CRF replaces the actual budget with a simple energy-balance equation. They used an inappropriate equilibrium approximation to their simple equation to argue that global mean surface temperature (GMST) and AMOC should be in phase. We show here that the exact solution to that same equation actually supports our claim on the relationship between the rate of change of GMST and the AMOC state, which they misunderstood as we claiming a negative correlation between GMST and AMOC themselves. They claimed, incorrectly, that a positive correlation coefficient, no matter how small and even though none of them is statistically significant, is strong evidence that the two time series are in phase. The correlation coefficients that they found using observational data (0.01, 0.28 and 0.45), though positive, correspond to out of phase, far from being in-phase. Visually they were made to look somewhat in-phase with decadal smoothing and short-period detrending. Both model and observational evidence supports the conclusion of our original paper that the period of AMOC minimum is a period of rapid rate of surface warming.

Changes in Atlantic Meridional Overturning Circulation (AMOC) affect tropical precipitation through the coupling with the Hadley Circulation and cross-equatorial atmospheric heat transport. Climate model simulations project a possible weakening of the AMOC under global warming. Here, we run model experiments with EC-Earth3 where we artificially weaken the AMOC through the release of a freshwater anomaly at high latitudes. The simulated AMOC collapse of ~57% for 60 model years allows us to investigate atmospheric heat and circulation readjustment to AMOC weakening and impacts on tropical precipitation, including the global monsoon. We find that the Inter Tropical Convergence Zone (ITCZ) shifts equatorward and tropical precipitation decreases over its northern flank while it increases southward due to reduced northward oceanic heat transport. Global monsoon is also impacted by AMOC weakening: Northern/Southern Hemisphere monsoons are weaker/stronger than the control experiment, with different sensitivities according to different regions: monsoons systems in the Atlantic sector are strongly impacted by AMOC decline. We further explore interbasin anomalies in the zonal/meridional atmospheric heat transport and net energy input triggered by the AMOC decline by examining local Hadley and Walker circulation asymmetries. Given that a ~57% reduction in the AMOC strength is within the inter-model range of future projections by the end of the 21st century, our results have important implications for understanding the role of AMOC in future tropical precipitation response. 

<p>The Atlantic Meridional Overturning Circulation (AMOC) is thought to exist in multiple states of equilibria. In the present climate, the AMOC is believed to be in a relatively strong state, bringing warm waters into the North Atlantic and contributing to mild winters over Europe. However, proxy data show evidence of abrupt declines in the strength of the AMOC, often associated with the initiation of ice ages. The abrupt shifts in the strength of the AMOC are usually referred to as ‘tipping points’. Presently, state-of-the-art climate models are unable to spontaneously reproduce tipping points in the AMOC, preventing an accurate study of the climate impacts of an abrupt AMOC shutdown. Contextually, although it is deemed unlikely that the AMOC will collapse in response to climate change, it is expected to further slow down into the 21<sup>st</sup> century. The impacts of this weakening, relative to those of global warming, are poorly understood, especially on daily timescales.</p><p>            To address this question, we run water hosing experiments with the EC-Earth3 earth system model to investigate the impacts of an AMOC abrupt weakening on the winter climate variability focusing on the North Atlantic and Europe. We confirm results from previous studies showing a large decrease in temperature, precipitation, and an increase in the jet stream over Europe. However, we further investigate the moisture budget and the impacts on daily weather regimes and blocking. In contrast to previous hypotheses, we find that the reduction in precipitation over Europe is due to changes in the storm tracks rather than thermodynamic effects. Further, we find a significant increase in the frequency and persistence of NAO+ days. Finally, we show precipitation and temperature extremes that are expected in response to the AMOC weakening.</p><p>            Our results show the climate impacts on weather events that can be expected from an AMOC weakening alone, and are relevant to understanding the relative roles of greenhouse gas forcing and AMOC weakening on the European climate in simulations of future climate change.</p>

Uncertainty in the strength of the Atlantic Meridional Overturning Circulation (AMOC) is analyzed in the Coupled Model Intercomparison Project Phase 3 (CMIP3) and Phase 5 (CMIP5) projections for the twenty-first century; and the different sources of uncertainty (scenario, internal and model) are quantified. Although the uncertainty in future projections of the AMOC index at 30°N is larger in CMIP5 than in CMIP3, the signal-to-noise ratio is comparable during the second half of the century and even larger in CMIP5 during the first half. This is due to a stronger AMOC reduction in CMIP5. At lead times longer than a few decades, model uncertainty dominates uncertainty in future projections of AMOC strength in both the CMIP3 and CMIP5 model ensembles. Internal variability significantly contributes only during the first few decades, while scenario uncertainty is relatively small at all lead times. Model uncertainty in future changes in AMOC strength arises mostly from uncertainty in density, as uncertainty arising from wind stress (Ekman transport) is negligible. Finally, the uncertainty in changes in the density originates mostly from the simulation of salinity, rather than temperature. High-latitude freshwater flux and the subpolar gyre projections were also analyzed, because these quantities are thought to play an important role for the future AMOC changes. The freshwater input in high latitudes is projected to increase and the subpolar gyre is projected to weaken. Both the freshening and the gyre weakening likely influence the AMOC by causing anomalous salinity advection into the regions of deep water formation. While the high model uncertainty in both parameters may explain the uncertainty in the AMOC projection, deeper insight into the mechanisms for AMOC is required to reach a more quantitative conclusion.

The Atlantic Meridional Overturning Circulation (AMOC) is projected to weaken in the future due to increasing greenhouse gas concentrations, but it is still debated whether anthropogenic climate change can induce an irreversible collapse or “tipping” of the AMOC. Meltwater from the Greenland ice sheet has often been invoked as a key mechanism for a potential AMOC tipping, but it is not explicitly represented in most state-of-the-art (CMIP6) climate models, adding further uncertainty to assessing the likelihood of irreversible AMOC change.Here, we perform ensemble simulations with the CMIP6 model EC-Earth3 to assess the effects of future Greenland ice sheet melt and to probe AMOC reversibility with and without Greenland meltwater. To this end, we force EC-Earth3 with a strong global warming scenario (SSP5-8.5) and a high-end Greenland meltwater estimate from the coupled climate–ice sheet model CESM2-CISM2 until 2300.We find that, as expected, the addition of Greenland meltwater significantly exacerbates the greenhouse gas-induced AMOC weakening especially after the 21st century, with differences mostly attributable to the Arctic Ocean. However, we find no indication of an abrupt AMOC weakening. We then branch off idealized reversibility experiments in which the meltwater and/or greenhouse gas forcings are reversed. Although the AMOC recovery is slow (around two centuries), meltwater-driven additional AMOC weakening in EC-Earth3 appears to be reversible. Regardless of the added meltwater, the AMOC also recovers in an idealized CO2 ramp-down experiment, even overshooting its present-day strength. While our modeling results show little support for an irreversible AMOC change due to future Greenland ice sheet melt, they do underline the importance of representing meltwater in future projections, including overshoot pathways.

The RAPID-MOCHA array monitors the Atlantic Meridional Overturning Circulation (AMOC) at 26.5°N by combining contributions from wind-driven Ekman transport, the Florida Current, and the mid-ocean geostrophic flow derived from tall moorings. While the Florida Current transport has been remarkably steady over the past decades and the Ekman transport has been strengthening since 2004, the AMOC has been weakening since 2004 when the RAPID-MOCHA observations started. This study investigates the role of buoyancy anomalies along the deep western boundary (DWB) on the observed AMOC decline. The DWB presents density features typical of both upper and lower North Atlantic Deep Water (uNADW and lNADW, respectively), which are water masses formed in the subpolar North Atlantic and tend to flow southward along the North Atlantic western boundary until reaching 26.5°N. The uNADW can be divided into upper Labrador Sea Water (uLSW) and classical LSW (cLSW). Since 2004, the DWB has been getting lighter, largely due to warming, but with varying effects of salinity on the uNADW and lNADW layers. To isolate the influence of these water mass changes on the AMOC, we recalculated the AMOC by substituting the western boundary density profiles in a given layer (e.g., uNADW, lNADW, uLSW, cLSW) with monthly climatological values and compared the resulting estimates to those derived from the full RAPID-MOCHA data set. Between 2004 and 2023, the observed AMOC weakened at a rate of −0.8±0.7 Sv/decade, with DWB density anomalies accounting for 77% of this trend (−0.6±0.1 Sv/decade). Further breakdown reveals that the lNADW contributes 47% (−0.39±0.07 Sv/decade) and the uNADW contributes 33% (−0.27±0.07 Sv/decade) to the overall AMOC decline. When the uNADW is subdivided, the cLSW influences the AMOC weakening by −0.38±0.09 Sv/decade, similar to the influence of the lNADW, while uLSW acts to strengthen the AMOC by 0.11±0.03 Sv/decade. Experiments isolating temperature and salinity anomalies indicate that temperature anomalies drive approximately two-thirds of the DWB-induced AMOC weakening, with salinity playing a secondary but important role in the lNADW. These findings suggest that southward advection of buoyancy anomalies formed in the Labrador and Nordic Seas account for about 75% of the AMOC weakening observed at 26.5°N between 2004 and 2023, particularly highlighting the influence of cLSW and lNADW water mass changes. The trend of the residual signal (joint influence of Florida Current, upper ocean, eastern boundary and Ekman transports) is not statistically significant, whereas the DWB and individual water mass influence trends are significant at the 99% confidence level.

While most models agree that the Atlantic meridional overturning circulation (AMOC) becomes weaker under greenhouse gas emission and is likely to weaken over the twenty-first century, they disagree on the projected magnitudes of AMOC weakening. In this work, CMIP6 models with stronger climatological AMOC are shown to project stronger AMOC weakening in both 1% ramping CO2 and abrupt CO2 quadrupling simulations. A physical interpretation of this result is developed. For models with stronger mean state AMOC, stratification in the upper Labrador Sea is weaker, allowing for stronger mixing of the surface buoyancy flux. In response to CO2 increase, surface warming is mixed to the deeper Labrador Sea in models with stronger upper-ocean mixing. This subsurface warming and corresponding density decrease drives AMOC weakening through advection from the Labrador Sea to the subtropics via the deep western boundary current. Time series analysis shows that most CMIP6 models agree that the decrease in subsurface Labrador Sea density leads AMOC weakening in the subtropics by several years. Also, idealized experiments conducted in an ocean-only model show that the subsurface warming over 500–1500 m in the Labrador Sea leads to stronger AMOC weakening several years later, while the warming that is too shallow (<500 m) or too deep (>1500 m) in the Labrador Sea causes little AMOC weakening. These results suggest that a better representation of mean state AMOC is necessary for narrowing the intermodel uncertainty of AMOC weakening to greenhouse gas emission and its corresponding impacts on future warming projections.

<strong class="journal-contentHeaderColor">Abstract.</strong> The Atlantic meridional overturning circulation (AMOC) is an important part of our climate system. The AMOC is predicted to weaken under climate change, however there are theories that it may have a tipping point beyond which recovery is difficult, hence showing quasi-irreversibility (hysteresis). Although hysteresis has been seen in simple models, it has been difficult to demonstrate in comprehensive global climate models. Here we outline a set of experiments designed to explore AMOC hysteresis and sensitivity to additional freshwater input as part of the North Atlantic hosing model intercomparison project (NAHosMIP). These experiments include adding additional freshwater (hosing) for a fixed length of time to examine the rate and mechanisms or AMOC weakening, and whether the AMOC subsequently recovers once hosing stops. Initial results are shown from eight climate models participating in the Sixth Coupled Model Intercomparison Project (CMIP6). The AMOC weakens in all models from the freshening, but once the freshening ceases, the AMOC recovers in half of the models, and in the other half it stays in a weakened state. The difference in model behaviour cannot be explained by the ocean model resolution or type, or by details of subgridscale parameterizations. Nor can it be explained by previously proposed properties of the mean climate state such as the strength of the salinity advection feedback. Instead the AMOC recovery is determined by the climate state reached when hosing stops, with those experiments where the AMOC is weakest not experiencing a recovery.

<strong class="journal-contentHeaderColor">Abstract.</strong> The Atlantic meridional overturning circulation (AMOC) is an important part of our climate system. The AMOC is predicted to weaken under climate change, however there are theories that it may have a tipping point beyond which recovery is difficult, hence showing quasi-irreversibility (hysteresis). Although hysteresis has been seen in simple models, it has been difficult to demonstrate in comprehensive global climate models. Here we outline a set of experiments designed to explore AMOC hysteresis and sensitivity to additional freshwater input as part of the North Atlantic hosing model intercomparison project (NAHosMIP). These experiments include adding additional freshwater (hosing) for a fixed length of time to examine the rate and mechanisms or AMOC weakening, and whether the AMOC subsequently recovers once hosing stops. Initial results are shown from eight climate models participating in the Sixth Coupled Model Intercomparison Project (CMIP6). The AMOC weakens in all models from the freshening, but once the freshening ceases, the AMOC recovers in half of the models, and in the other half it stays in a weakened state. The difference in model behaviour cannot be explained by the ocean model resolution or type, or by details of subgridscale parameterizations. Nor can it be explained by previously proposed properties of the mean climate state such as the strength of the salinity advection feedback. Instead the AMOC recovery is determined by the climate state reached when hosing stops, with those experiments where the AMOC is weakest not experiencing a recovery.

Observations over the last 40 years show that the Atlantic Ocean salinity pattern has amplified, likely in response to changes in the atmospheric branch of the global water cycle. Observational estimates of oceanic meridional freshwater transport (FWT) at 26.5° N indicate a large increase over the last few decades, during an apparent decrease in the Atlantic Meridional Overturning Circulation (AMOC). However, there is limited observation based information at other latitudes. The relative importance of changing FWT divergence in these trends remains uncertain. Ten models from the Coupled Model Intercomparison Project Phase 5 are analysed for AMOC, FWT, water cycle, and salinity changes over 1950–2100. Over this timescale, strong trends in the water cycle and oceanic freshwater transports emerge, a part of anthropogenic climate change. Results show that as the water cycle amplifies with warming, FWT strengthens (more southward freshwater transport) throughout the Atlantic sector over the 21st century. FWT strengthens in the North Atlantic subtropical region in spite of declining AMOC, as the long-term trend is dominated by salinity change. The AMOC decline also induces a southward shift of the Inter-Tropical Convergence Zone and a dipole pattern of precipitation change over the tropical region. The consequent decrease in freshwater input north of the equator together with increasing net evaporation lead to strong salinification of the North Atlantic sub-tropical region, enhancing net northward salt transport. This opposes the influence of further AMOC weakening and results in intensifying southward freshwater transports across the entire Atlantic.

Recent work has shown that the weakening of the Atlantic meridional overturning circulation (AMOC) under anthropogenic climate change is sensitive not only to the amount of atmospheric CO 2 increase but also to the rate of CO 2 increase. In this work, we explicitly test whether a previously proposed AMOC–sea ice feedback controls the AMOC’s sensitivity to the rate of CO 2 increase using mechanism-denial experiments in a global climate model. We find that when the AMOC–sea ice feedback is suppressed, the AMOC is nearly insensitive to the rate of CO 2 increase, supporting the hypothesis that this feedback is the primary reason for the AMOC’s sensitivity to the rate of CO 2 increase. Additionally, we show that the reduction of sea ice meltwater in the North Atlantic that is caused by the retreat of Arctic sea ice in a warming climate constitutes a large strengthening forcing on the AMOC, reducing the total amount of AMOC weakening by nearly half. The strong influence of sea ice meltwater on the AMOC—both in its role as a forcing and a feedback—occurs through the ability of the meltwater to modulate how much surface water mass transformation occurs via ocean heat loss to the atmosphere over the deep convection zones in the North Atlantic. This work demonstrates that Arctic sea ice–AMOC interactions are a first-order control on future AMOC weakening and highlights the importance of constraining present-day sea ice meltwater fluxes to assess their potential counteracting influence on the weakening of Earth’s AMOC. Significance Statement In this work, we aim to understand how Arctic sea ice influences the weakening of the Atlantic meridional overturning circulation (AMOC) under future anthropogenic greenhouse gas emissions. We find that when Arctic sea ice and the AMOC are allowed to mutually influence each other in a positive feedback cycle, the amount of AMOC weakening is highly sensitive to the rate of CO 2 change (even when the CO 2 concentration is the same). We also show that the retreat of sea ice under global warming can counteract some of the AMOC weakening induced by CO 2 increases. This work highlights how understanding the fundamental mechanisms of AMOC–sea ice interactions is critical for constraining the future weakening of Earth’s AMOC.

The Atlantic Meridional Overturning Circulation (AMOC) plays an important role in the global climate by transporting heat northward. According to the latest IPCC report (AR6) the strength of the AMOC is very likely to weaken by 2100 (Fox-Kemperer et al. 2021). A weaker AMOC would significantly impact local and global climate. However, there is large model spread in the magnitude of the projected reduction in AMOC strength (Weijer et al. 2020) so it is unclear to what extent the AMOC will weaken by the end of the 21st century.This study investigates the spread in AMOC response among CMIP6 models. As an initial step we investigated the model correlations of AMOC weakening across different ScenarioMIP experiments. Preliminary results show that the decline for similarly forced scenarios, such as ssp370 and ssp585, have stronger correlations than for scenarios with significantly different forcing, such as ssp126 and ssp585.Further analyses into the relationship between the projected weakening and model biases in ocean temperature,&amp;#160; salinity and meridional density gradients are performed. In addition, we investigate how the weakening correlates with possible drivers. A better understanding of how model biases influence AMOC changes will allow for more accurate projections of future AMOC changes and their impacts, as well as improved understanding of what the driving processes of the weakening are in various models.