Projections from global climate models reveal a significant inter-model spread in future rainfall changes in the tropical Atlantic by the end of the 21 st century, including alterations to the Intertropical Convergence Zone (ITCZ) and monsoonal regions. While existing studies have identified various sources of uncertainty, our research uncovers a prominent role played by the decline of the (AMOC) for the intermodel spread. Firstly we examine 30 climate model simulations (using the ssp5-8.5 scenario) from the CMIP6 archive and show that models that present a more substantial AMOC decline exhibit an equatorward shift of the ascending branch of the Atlantic regional Hadley circulation, resulting in a southward displacement of the ITCZ. Conversely, models characterized by a smaller AMOC decline do not indicate any ITCZ displacement. Secondly, we use targeted experiments (using the abrupt 4xCO2 experiment) to specifically isolate the effects of a weakened AMOC from the changes in precipitation that would occur if, under continuous global warming, the AMOC did not weaken. Our results demonstrate that net precipitation anomalies in the abrupt 4xCO2 experiments are displaced southwards compared to the simulation with fixed AMOC strength, corroborating our previous findings. Our study has implications for understanding the mechanisms driving future changes in tropical Atlantic precipitation, and underscores the central role played by the AMOC in future climate change. (ITCZ) is a planetary-scale zonal band of intense precipitation activity. Typically, the ITCZ is located about 5 deg north of the equator in the annual mean (Philander et al. (1996)). However, its location undergoes migration in response to solar insolation and inter-hemispheric energy imbalance (Broccoli et al., (2006); Chiang et al. (2012), Bischoff and Schneider (2014)). Modifications in the strength, width, and seasonal displacements of the ITCZ can have far-reaching impacts, including severe droughts or extensive flooding, with significant implications for local communities (Fernandes et al. (2011), Marengo et al. (2012), Chiang (2002)). Atmospheric reanalyses and observations indicate recent intensification and narrowing of the ITCZ. For the coming years, idealized climate model simulations of future climate change generally project further narrowing and weakening of the mean ascent (Byrne et al. (2018), Mamalakis et al. (2021), Byrne and Schneider (2016)). Nonetheless, previous studies have revealed significant inter-model uncertainty in simulating the response of tropical precipitation to future climate change. For instance, Byrne et al. (2018) demonstrated inter-model uncertainty in the meridional shift of the ITCZ in a warming climate using models from the phase 5 (CMIP5) (Taylor et al. (2012)), while Mamalakis et al. (2021) found that the inter-model spread persists in CMIP6 models (Eyring et al. (2016), O'Neill et al. (2016)). Previous research has established that the meridional position of the ITCZ in the mean climate is influenced by the inter-hemispheric energy transport (Donohoe et al. (2013), Donohoe (2016), Donohoe and Voigt (2017)). Given its influence on cross-equatorial heat transport, the (AMOC) is thus believed to play a pivotal role in governing the ITCZ's position and meridional displacements (Frierson et al. (2013), Marshall et al. (2014), Schneider et al. (2014), Yu et al. (2019), E. Moreno-Chamarro et al. (2020)). In fact, in the mean climate the AMOC transports ~0.5 PW of heat into the Northern Hemisphere (Buckley and Marshall, 2016). In addition, several prior studies have employed climate models to conduct ad-hoc experiments to investigate the impacts of reduced energy transport by the AMOC on precipitation. These studies demonstrated that a weakened AMOC results in reduced precipitation over the North Atlantic and a southward shift of the ITCZ's zonal mean position over the tropical ocean (e.g., Vellinga and Wood (2002), Zhang and Delworth (2005), Stouffer et al. (2006), Parsons et al. (2014), Jackson et al. (2015), Good et al. (2021), Orihuela-Pinto et al. (2022)). A southward shift of the ITCZ balances the reduced northward heat transport by the AMOC, and is associated with a meridional displacement of the Hadley Cells and an intensification of the ascending branch of the (Zhang and Delworth 2005, Bellomo et al. 2023, Lionello et al., 2024). Consequently, the response of the AMOC to climate change might significantly impact the tropical Atlantic ITCZ in future climate scenarios, considering the general consensus among climate models on a substantial weakening of the AMOC by the 21 st century (Weijer et al. (2020), Rahmstorf et al. (2015), Caesar et al. (2018), Bellomo et al. (2021)). In particular, Bellomo et al. (2021) investigated abrupt 4xCO2 simulations from the CMIP5 and CMIP6 archives and demonstrated that a sufficiently strong decline in the AMOC intensity can modulate the global precipitation response. Furthermore, idealized experiments with one global climate model showed that a weakened AMOC, relative to rising greenhouse gases, can lead to a southward shift of the tropical Atlantic ITCZ in the annual mean (Liu et al. 2020, Bellomo andMehling 2024). The specific role that the representation of the AMOC plays in the large inter-model spread in Atlantic ITCZ projections of the current century has remained largely unexplored, despite the potential significance of the AMOC's response to increasing greenhouse gases (Wang et al. (2014)). In this study we address this gap by employing a set of 30 latestgeneration global climate models to examine the ssp5-8.5 high-emission scenario, where the AMOC undergoes substantial weakening by 2100, though the extent of its weakening is uncertain across models. Through this multi-model approach, we group models based on the magnitude of AMOC decline, revealing that the spread in the representation of AMOC decline is tightly linked to inter-model differences in anticipated changes of both tropical rainfall and mean atmospheric circulation over the Atlantic sector. Nevertheless, in these simulations it is challenging to isolate the precipitation response due to AMOC decline from that due to other climate feedbacks related to anthropogenic forcing and ongoing climate change. Therefore, to build consistency on our findings, we supplement our analysis with idealized model experiments using EC-Earth3, a global climate model that participates in CMIP6. We examine the annual mean tropical Atlantic rainfall response to the AMOC decline in an ensemble of 30 model simulations from the CMIP6 archive (Eyring et al. (2016)).
We compare the shared socio-economic pathway ssp5-8.5 experiment with the historical run. The historical experiment was forced with observed estimates of human-induced and natural radiative forcings from 1850 to 2014 (O' Neill et al. (2016)). The ssp5-8.5 future projection spans the years between 2015 and 2100, and was forced with estimates of greenhouse gas concentrations assuming a high emission scenario reaching a radiative forcing at the top of atmosphere of 8.5 W/m2 by the end of the 21 st century. The ssp5-8.5 experiment was initialized from the last year of the historical experiment. We analyze all 30 models that made available the variables needed for this study. Where available, we pick the r1i1p1f1 ensemble member. The list of models and the relative ensemble member is provided in In addition to the ssp5-8.5 simulations, we analyze two experiments carried out with the global climate model EC-Earth3. These experiments were started from the preindustrial control ("piControl") experiment (ensemble member r1i1p1f1) from the CMIP6 archive. The piControl experiment spans 500 years during which all the external radiative forcings are maintained at pre-industrial levels (CO2 at ~ 284 ppm). In the first experiment, the CO2 was abruptly quadrupled from the mean annual preindustrial level and was held fixed for 150 years ("abrupt 4xCO2") (Eyring et al., 2016). This experiment is stored in the CMIP6 archive (ensemble member r81i1p1f1). The second one is an ad-hoc experiment that aims at maintaining the AMOC strength fixed at the preindustrial level, despite an abrupt fourfold increase in atmospheric CO2 applied as external forcing. This was achieved by adding a virtual salinity flux poleward of 50 deg N in the North Atlantic and Arctic Oceans. We ran a small ensemble of 3 members for the second experiment. Although the 3 members share the same configuration as the EC-Earth3 version used in CMIP6 and initial conditions, they were forced with salinity fluxes of slightly different magnitudes (+0.4Sv, +0.5Sv, and +0.6Sv) to span the model's internal variability of AMOC strength in the preindustrial simulation (Meccia et al. 2022). We analyzed each member individually and found no large differences among them. Therefore, only results from the ensemble mean of the 3 members are presented hereafter, referred to as the "PI-fixed AMOC" experiment. The abrupt4xCO2 and PI-fixed AMOC experiments allow us to separate the response of tropical rainfall to CO2 forcing, from the response to an AMOC weakening due to the same forcing, thereby isolating the impacts of the AMOC weakening on tropical rainfall. Note that these experiments are identical to those shown in Bellomo and Mehling (2024) and we refer the reader to that publication for further technical details. Timeseries of AMOC strength in the ssp5-8.5 and EC-Earth3 idealized experiments are shown in For the 30 ssp5-8.5 simulations, we define the control climatology as the time-mean from the whole historical simulations (165 years spanning from 1850 to 2014). For each model, we compute changes as the difference between the mean of years 2071 through 2100 (30 years) of the ssp5-8.5 simulation and the control climatology. To ensure changes do not lie within the natural climate variability, we perform a Student's t-test between the historical and the future timeseries, using a significance level of 90%. All model output is interpolated to a common 2.5 deg x 2.5 deg latitude/longitude grid before performing the analysis. To assess the impacts of the AMOC decline in the CMIP6 ssp5-8.5 scenario, relative to other changes, we create 2 groups of 10 models each (out of the 30 models employed in this study), based on the amount of the AMOC decline with respect to the control climatology (see Tab.1). The models belonging to the group in which the AMOC declines less are hereafter referred to as "SAD" (small AMOC decline), while the models belonging to the group in which the AMOC declines more are hereafter referred to as "LAD" (large AMOC decline). The remaining 10 models display intermediate values of AMOC decline, and do not belong to any group. In this study, we define the AMOC strength index as the maximum value of the overturning streamfunction at 26.5 deg N and below 500m depth (Buckley and Marshall 2016). Fig. 1 shows timeseries of AMOC strength, and models are coded with line types based on which group they belong to. Detailed information on AMOC strength changes in each model is also provided in We note that dividing by GMTAS also reduces the influence of the global climate feedback on our results, helping to isolate the effect of AMOC on ITCZ changes by mitigating the response to increased CO2. Thus, where statistically significant, we deem the differences in simulated precipitation impacts to arise from the difference in AMOC decline (c.f. Bellomo et al., 2021). Alternatively, we also conduct a bootstrap test to further check whether the differences between the two groups of models are significantly different from the 1000 differences of two randomly chosen groups, and results are consistent with the t-test. For what concerns the abrupt 4xCO2 and the PI-fixed AMOC experiments with EC-Earth3, we compute changes as the difference between time means over model years 50 to 150, covering years in which the weakened AMOC strength is in nearly steady, and the corresponding control climate, here defined as long-term means of the whole piControl run (500-year period). Again, we perform a Student's t-test (at 90% significance level) between the control and the idealized experiments timeseries, to ensure that changes are not part of the model's internal climate variability. Time series of AMOC strength in the EC-Earth3 experiments are also shown in To investigate the role of a weakening AMOC in shifting the ITCZ in the meridional direction in the ssp5-8.5 simulations, we evaluate the correlation coefficient and the strength of the linear regression between the magnitude of the AMOC decline and the difference in net precipitation (P -E) anomalies in two adjacent areas in the Atlantic deep tropics, where the P -E change differences between the models are the strongest (see boxes in fig. 3d).
These regions are meridionally displaced and have coordinates (30 deg W -8 deg W, 12 deg N -3 deg N) and (47 deg W -25 deg W, 3 deg N -6 deg S). We compute the differences as the area-averaged P -E anomalies in the southern box minus those in the northern box. To investigate the mechanisms driving changes in P -E we perform the atmospheric moisture budget as derived in D'Agostino and Lionello (2020). Here we provide only a short overview of this method, pointing the reader to D'Agostino and Lionello (2020) and references therein for a more in-depth derivation. To compute the moisture budget, the anomalies are computed by monthly mean outputs, the following equation is used: Where P is precipitation, E is evaporation, u is the wind vector, q is specific humidity, p 0 is the surface pressure field,  ! is the density of water, and g is the gravity acceleration. Here,  denotes differences between the simulations (i.e., ssp5-8.5, PI-fixed AMOC, abrupt 4xCO2) and their reference control climatology (i.e., historical, piControl). Through equation ( 1) we can decompose P -E change as the sum of four drivers. The thermodynamic contribution (TH) reflects changes in the mean humidity and includes changes of humidity gradient along the direction of the mean flow and changes of mean humidity in areas of mean flow convergence or divergence (i.e, constrained by the Clausius-Clapeyron relation). The dynamic contribution DY involves changes in the mean meridional circulation and moisture transported by the mean wind flow. The transient eddies (TE) and nonlinearities (NL) are instead due to changes in the covariance of sub-monthly humidity and wind anomalies. Since the TE + NL term cannot be computed explicitly from monthly data we have used the approach of D'Agostino and Lionello (2020), where it is estimated as: while the surface contribution (S) is computed as the residual: To estimate the AMOC influence on each of these contributions to the total P -E change, we compute the anomalous moisture budget for both the SAD and LAD groups and the PI-fixed AMOC and the 4xCO2 experiments; then, we analyze the respective differences. Concerning the SAD and LAD groups, we consider changes significant if at least two-thirds of the models agree in the sign of change. We note that for the GISS-E2-1-G we encountered unrealistic fluxes over land, hence for this model we included only values over the ocean. We investigate the dynamic contribution of the atmospheric mean flow over the Tropical Atlantic Ocean with an analysis of the atmospheric mass streamfunction, which is closely related to the mean Hadley circulation. To compute the meridional streamfunction in a regional domain (i.e. in the Atlantic sector), the assumption of nondivergent meridional circulation, which is essential to ensure mass conservation in the computation of the Stokes streamfunction, is invalid. Thus, we follow the approach of Zang and Wang (2013), Schwendike et al. (2014) and Nguyen et al. (2018), to partition the three-dimensional circulation into two divergent circulations lying in orthogonal planes that satisfy continuity independently. Through the Helmholtz decomposition, we extract the irrotational component of the meridional wind flow (i.e., the only contribution to the vertical flow), which can be regarded as the meridional overturning circulation. The Hadley overturning can be represented by a streamfunction computed from the divergent meridional wind similar to the Stokes streamfunction: where R is Earth's radius, g is the standard gravity, p % is pressure at the top of troposphere, p 0 is the surface pressure field, v 2 is the divergent meridional wind, and y is latitude. Brackets refer to a zonal average over a specified limited domain. In this study we select longitudes ranging between 60 deg W and 10 deg E. The timeseries of the annual mean AMOC index at 26.5 deg N in all the ssp5-8.5 simulations reveal a substantial AMOC weakening occurring by the end of the current century, although a great inter-models spread exists . The highest AMOC decline corresponds to a change in strength of about -63%, and the lowest change is about -22%. The mean change of all models corresponds to about -42% of AMOC strength reduction, with a median of -44%. In Figure 1, solid curves represent the models in which the amount of AMOC reduction belongs to the lower tercile of the distribution of all models (LAD models, AMOC reduction ranges from -8.5 Sv and -13.4 Sv). The dashed curves, on the other hand, represent the models that belong to the upper tercile (SAD models, AMOC reduction ranges from -4.3 Sv and -6.1 Sv). Dotted colored lines represent models in the middle of the range of AMOC declines and do not belong to any groups. Note that models belonging to the LAD group (i.e. models in which the AMOC declines more) also exhibit a stronger AMOC in the climatology (c.f. solid contours in fig. 2), which is consistent with previous studies (e.g., Weijier et al. 2020). As expected, the EC-Earth3 PI-fixed AMOC experiment (dashed black curve) is the only simulation where the AMOC strength, despite increasing greenhouse gases in the background, does not decrease. On the contrary, in the EC-Earth3 abrupt 4xCO2 simulation (solid black curve) the AMOC decreases significantly (~ -7 Sv of change, corresponding to a 43% reduction). A decline of 7 Sv is comparable with that of models belonging to no group . In the SAD group P -E intensifies over the ocean close to the western African coast, but decreases all over the Atlantic sector and Amazon. Overall, models with a small AMOC decline project a drying tendency of the climatological ITCZ (here intended as the tropical region where the annual-mean moisture convergence occurs, i.e. the moisture ITCZ (Schneider and Byrne (2016)), over the western side of the Atlantic basin and an intensification over the eastern side at positive latitudes resulting in a drier tropical Atlantic equator. We note that this thermodynamic constraint is less robust over land, as reported in previous studies (Byrne and O' Gorman (2015)).
In contrast, the LAD group exhibits a southwards shift in P -E, featuring increased P -E right at the equator and drying tendencies at higher latitudes. The maximum of the tropical Atlantic precipitation change We perform both a robust Hubert regression (y = -0.061 x -0.435 ) with a R 2 of 0.60 , which excludes outliers, and a linear regression analysis (y = -0.052 x -0.413, not shown in Figure 4a), with a statistically significant R 2 of 0.46, which includes all models except for the abrupt 4xCO2 EC-Earth3 experiment. The regression analysis supports the importance of inter-model differences in AMOC decline in shaping tropical precipitation spatial distribution. Specifically, larger AMOC declines result in a more pronounced southward shift of the moisture ITCZ over the Atlantic, being therefore a fundamental factor in order to understand projected future changes. Moreover, Figure S1 shows P -E change regressed onto the AMOC decline, further supporting this result. We also note that results are similar if we use precipitation instead of P -E (Figure S2). that is, where less than two-thirds of the models agree on the sign of the change. TH in all models DY in all models TH in SAD models DY in SAD models Changes in P -E appear to be driven by different processes depending on how much the AMOC declines. To investigate these mechanisms, we apply an atmospheric moisture budget to model data (c.f. D'Agostino and Lionello 2020). This allows us to separate thermodynamic (TH) from dynamic contributions (DY), and to further quantify changes resulting from transient eddies and nonlinearities (TE + NL). Since TE + NL and the residual are small, in the main text we only show TH and DY, while the other terms can be found in Figure S3. Focusing on changes over the ocean, Figures 5a, 5b and 5c display consistent spatial patterns of P -E change, indicating that the TH term contributes primarily by intensifying the hydrological cycle (e.g., Held and Soden (2006)). The strength of anomalies is slightly different among these panels, although the normalization by GMTAS helps to limit this effect. It is worth noting that LAD models exhibit more warming in the tropical Atlantic compared to SAD models, implicating stronger thermodynamic changes (cf. figs. 5b and 5c). Nevertheless, we can conclude that TH drives precipitation impacts independently of the amount of AMOC weakening in these models. In contrast, the DY term shows substantial differences among the three panels (figs. 5d, 5e and 5f). In the "all models" panel , a zonal asymmetry appears between 35 deg W and 10 deg W, along with a drying tendency near the coasts of South America. This pattern represents the average effect of various processes. Specifically, the SAD group displays a strong dynamical drying signal near the eastern South American coasts, extending throughout the deep tropics of the Atlantic and intensifying towards the Gulf of Guinea. Instead, the dynamic component of the LAD group exhibits a meridional dipolelike structure located between the equator and 10 deg N, resembling the "all models" panel but with stronger anomalies at the equator. Furthermore, we observe similarities between Figures 3a and 5e (P -E changes and DY changes for the SAD group), particularly the drying signal along the American coasts, and between Figures 3b and 5f, showing the (dynamical) equatorial moistening displayed by the LAD ensemble. These findings underscore the substantial impact of dynamic drivers on the P -E changes in the tropical Atlantic. In the case of a smaller AMOC decline, the deep tropical Atlantic experiences dynamic drying, while a larger AMOC decline favors DY-induced moistening of the equator, achieved through the southward migration of the ITCZ (c.f. Figure 4a). The dynamic term DY appears to play a prominent role in causing differences in P -E changes between the SAD and LAD groups. Because DY quantifies changes in the columnintegrated moisture transported by the mean flow, which in the Tropics mostly occurs in the lower branches of the Hadley cells, here we investigate changes in the meridional overturning atmospheric mass streamfunction across longitudes ranging from 60 deg W to 10 deg E. To achieve this, we adopt the approach outlined by Zhang and Wang (2013), and further developed by Figures 6a and 6b show the Atlantic mass streamfunction changes (MSF) for the SAD and LAD groups, respectively. Superimposed black contour lines represent the mean atmospheric circulation computed from the historical simulation from all models. The climatological ascending branches of the northern and southern hemisphere annual mean Hadley cells converge at around 5 deg N, roughly corresponding to the meridional position of mean annual peak of Atlantic precipitation. We now focus on this region and nearby latitudes to explore changes in the mass streamfunction associated with changes in the position of the ITCZ. In the LAD group , positive (clockwise) anomalies between the equator and 5 deg N indicate that the Northern Hemisphere cell strengthens close to the equator whereas the Southern Hemisphere cell weakens. Specifically, the clockwise anomalies at the interface between the two cells suggest a squeezing of the climatologically cross-equatorial mean annual Southern Hemisphere Cell southwards, while the Northern Hemisphere Cell expands. We note that the SAD group does not show significant changes in cell intensity in this region. Instead, both the SAD and LAD groups exhibit a broad weakening of the Hadley cells, reflecting the slowdown of the tropical overturning circulation in a warming climate (c.f. Lu et al. 2007, Byrne et al. 2018). In LAD models, the reduction in cross-equatorial ocean heat transport caused by the weakened AMOC influences the Atlantic Hadley Circulation, possibly leading to a southward shift of the ascending branch in its annual mean (i.e. the Southern Hemisphere Hadley cell tends to become less cross-equatorial). Thus, the dynamical DY contribution to the meridional displacement of P -E change (i.e. the southward shift of the Atlantic ITCZ) may be explained by changes in the Atlantic atmospheric overturning circulation in the group of models featuring a relatively large AMOC decline.
We note that when evaluated globally, the atmospheric circulation anomalies show a similar pattern of change, but differences between the groups are less statistically significant (Figure S4 4b an ensemble of models, some differences are expected. But overall both figures suggest a fingerprint of the AMOC decline on the southward shift of the ITCZ in a warming 21 st century. Notably, a major effect of a strong AMOC slowdown as occurs in the abrupt 4xCO2 simulation is the reduced warming in the subpolar North Atlantic (Liu et al. 2020, Bellomo et al. 2021), because the northward transport of heat by the ocean is reduced. Thus, in this experiment, the southward shift of the ITCZ reflects the altered inter-hemispheric energy transport. The spatial distribution of the DY contribution to the moisture budget (panels 8d and 8e) is similar in the two experiments. Both panels show a drying signal between 10 deg S and 10 deg N that is reminiscent of that seen in the DY contribution derived from the all-models ensemble mean future projections , except for the positive anomaly being displaced near the South American coast in the EC-Earth3 experiments. Note that in the 4xCO2 this positive signal is broader and more intense between the equator and South America. Fig. 8f shows the DY difference between the abrupt 4xCO2 and PI-fixed AMOC experiments, which allows us to assess the weakened AMOC impact on the column-integrated atmospheric moisture transport. Between the two Hemispheres a bipolar seesaw, with adjacent positive/negative differences that change in sign around 7 degrees north, indicates a stronger dynamical moistening of the equatorial latitudes occurring in the abrupt 4xCO2 experiment. Therefore, fig. 8f demonstrates that an AMOC weakening alone causes changes in the atmospheric circulation that lead to a southward shift of the tropical moisture ITCZ, also in a 4xCO2 forced warmer climate. Previous studies have found that in climate change projections from the CMIP5 and CMIP6 models, there is large uncertainty in tropical Atlantic precipitation change, including the meridional dislocation of the ITCZ (e.g., Byrne et al. 2018, Mamalakis et al. 2021). One study (Good et al. 2021) Kelvin of global-mean surface-air warming, with an interquartile range across models of 0.46 deg /K. Of the models which they analyzed, 17 out of 32 predicted a northward ITCZ shift by the end of the 21 st century, while the remaining models predicted a southward shift. This near-even split between models results in great uncertainty regarding the direction of the ITCZ shift by the end of the 21 st century, which has significant implications for regional hydroclimate changes. In our study, we demonstrate that a southward shift of the Atlantic ITCZ is driven by changes in the mean meridional atmospheric circulation, specifically the Atlantic regional Hadley circulation, but only in models featuring a relatively larger AMOC decline. Although we did not specifically examine global-scale ITCZ changes, Figure S4 indicates a southward shift of the on a global scale in models with relatively larger AMOC declines. Therefore, when comparing our results with Byrne et al. 2018 and the latest AR6 IPCC report (IPCC 2022), we posit that the inter-model spread in the meridional displacement of the ITCZ may, in part, be attributed to the inter-model spread in AMOC decline. Moreover, beyond meridional shifts, we observe that the AMOC decline also modulates the intensity, spatial structure, and zonal migrations of P -E change. Recent studies (e.g., Nicknish et al., 2023) suggest that AMOC reduction, coupled with eastern equatorial Pacific warming, acts as a key driver of zonal and meridional energy flux shifts, which in turn mirror gross distributional changes of tropical precipitation. Therefore, differences in zonal shifts of P -E between the two groups may arise from inter-model differences in eastern equatorial Pacific warming (c.f. Bellomo et al., 2021), affecting trade wind patterns over the Atlantic. Our findings suggest that, under future global warming, the degree of compensation between thermodynamic (TH) and dynamic (DY) contributions, which is fundamental to understand future African monsoon precipitation (D'Agostino et al. 2019, D'Agostino et al. 2020), is potentially impacted by the AMOC slowdown effect on DY. The ssp5-8.5 simulations also reveal that a significant weakening of the AMOC leads to reduced annual mean rainfall in the Amazon region, which aligns with findings from idealized climate model experiments in which the AMOC is artificially suppressed (e.g., Vellinga and Wood (2002), Parsons et al. (2014), Jackson et al. (2015)). However, the difference in precipitation change simulated by the EC-Earth3 experiments does not agree with this result, therefore caution is needed when attributing it to the declining AMOC. Finally, we assert that the AMOC plays a crucial role as a key driver of inter-model uncertainty in projections of future tropical Atlantic precipitation changes. Our study shows that targeted experiments are needed to specifically investigate climatic impacts of the AMOC decline relative to anthropogenic global warming. We also suggest that in order to understand the impacts of the AMOC on tropical Atlantic hydroclimate, continued observational campaigns (McCarthy et al., 2015;Frajka-Williams et al., 2019;Li et al., 2021) are essential. An observational constraint on the AMOC response to future climate change would be beneficial for reducing inter-model uncertainty in its impacts. We acknowledge the 's Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1 of this paper) for producing and making available their model output. We acknowledge the 's Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1 of this paper) for producing and making available their model output. CMIP6 data openly available in CMIP6 archives at Relevant dataset generated and analysed for the The authors declare that they have no relevant financial or non-financial interests to disclose. wrote the first draft of this manuscript, and all authors contributed to edit and finalize the manuscript. All authors read and approved the final manuscript.
All code for data analysis associated with the current work can be requested by writing to the corresponding author. CMIP6 data openly available in CMIP6 archives at Relevant dataset generated and analysed for the The authors declare that they have no relevant financial or non-financial interests to disclose. wrote the first draft of this manuscript, and all authors contributed to edit and finalize the manuscript. All authors read and approved the final manuscript. All code for data analysis associated with the current work can be requested by writing to the corresponding author.