Overturning Pathways Control AMOC Weakening in CMIP6 Models

Baker, Jonathan A.; Bell, Michael; Jackson, Laura; Renshaw, Richard; Vallis, Geoffrey K.; Watson, Andrew J.; Wood, Richard

doi:10.1029/2023gl103381

Cited by 12 publications

(8 citation statements)

References 88 publications

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“…On the contrary, GISS-E2-1-G simulates a weakening of the NA/SA temperature gradient and an increase in aridity over northern Africa, in line with an abrupt decline of the AMOC (figure S11). This is consistent with Baker et al (2023), who show that changes in the AMOC are weak for CanESM5 and strong for GISS-E2-1-G, and with MIROC6 showing a change in the AMOC that is in the middle of the CMIP6 distribution. We thus suggest that the GHG effects on the future change of the AMOC explain a large part of the uncertainty for future change of NAF aridity, following the results of Bellomo et al (2021) and Swingedouw et al (2021).…”

Section: Discussionsupporting

confidence: 91%

An uncertain future change in aridity over the tropics

Monerie,

Chadwick,

Wilcox

et al. 2024

Environ. Res. Lett.

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An ensemble of climate models from phase six of the Coupled Model Intercomparison Project shows that temperature and potential evapotranspiration are projected to increase globally towards the end of the 21st century. However, climate models show a spatially heterogeneous change in precipitation over the tropics. Consequently, future changes in aridity (a measure of water availability) are complex and location-dependent. We assess future changes in aridity using three climate models and several single-forcing experiments. Near-term (2021-2040) changes in aridity are small, and we focus instead on its long-term (2081-2100) changes. We show that the increase in greenhouse gases primarily explains the spatial pattern, magnitude and ensemble spread of the long-term future changes in aridity. On this timescale, the effects of changes in emissions of anthropogenic aerosols are moderate compared to the effects of increases in atmospheric greenhouse gas concentrations. Model diversity in the responses to greenhouse gas concentration is large over northern Africa and North and South America. We suggest the large uncertainty is due to differences between models in simulating the effects of an increase in greenhouse gas concentrations on surface air temperature over the North Atlantic Ocean, on the interhemispheric temperature gradient, and on potential evapotranspiration over North and South America.

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Section: Discussionsupporting

confidence: 91%

An uncertain future change in aridity over the tropics

Monerie,

Chadwick,

Wilcox

et al. 2024

Environ. Res. Lett.

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“…While these studies largely attribute this link to Southern Ocean processes (Kuhlbrodt & Gregory, 2012; Newsom et al., 2023; Saenko et al., 2018), it suggests that constraining H might constrain the transient climate response. Furthermore, numerous studies have shown that the mean‐state AMOC strength is related to AMOC weakening under warming, implying that, regardless of the mechanisms setting the contemporary AMOC strength, this strength may be predictive of future AMOC declines (Baker et al., 2023; Bonan et al., 2022; Gregory et al., 2005; Weaver et al., 2012; Weijer et al., 2020; Winton et al., 2014). Thus, our work implies that improving mean‐state processes that impact H , whether it be locally in the North Atlantic or non‐locally in the Southern and Indo‐Pacific Oceans, will ultimately lead to a better understanding of how the AMOC changes under warming.…”

Section: Discussionmentioning

confidence: 99%

“…The large intermodel spread in both the strength and structure of the mean‐state AMOC leads to a key question: What causes the intermodel spread in the mean‐state AMOC strength across GCMs? Given that the mean‐state AMOC strength is linked to the magnitude of AMOC weakening under warming in GCMs (e.g., Baker et al., 2023; Gregory et al., 2005; Weijer et al., 2020; Winton et al., 2014), a better understanding of mean‐state AMOC processes may improve future climate projections.…”

Section: Introductionmentioning

confidence: 99%

Controls on the Strength and Structure of the Atlantic Meridional Overturning Circulation in Climate Models

Nayak,

Bonan,

Newsom

et al. 2024

Geophysical Research Letters

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State‐of‐the‐art climate models simulate a large spread in the mean‐state Atlantic meridional overturning circulation (AMOC), with strengths varying between 12 and 25 Sv. Here, we introduce a framework for understanding this spread by assessing the balance between the thermal‐wind expression and surface water mass transformation in the North Atlantic. The intermodel spread in the mean‐state AMOC strength is shown to be related to the overturning scale depth: climate models with a larger scale depth tend to have a stronger AMOC. We present a physically motivated scaling relationship that links intermodel variations in the scale depth to surface buoyancy fluxes and stratification in the North Atlantic, and thus connects North Atlantic surface processes to the interior overturning circulation. Climate models with a larger scale depth tend to have stronger surface buoyancy loss and weaker stratification in the North Atlantic. These results offer a framework for reducing mean‐state AMOC biases in climate models.

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“…Over the northern Atlantic, most ESMs project a stronger decrease in SSTs relative to the decrease in GMST after peak warming as compared to before peak warming. As greenhouse gas emissions rise, the AMOC weakens, leading to a cooling in the northern Atlantic and northern Europe [39,40]. In most ESMs the AMOC recovers when global mean temperatures decrease, however, with a considerable time lag [41].…”

Section: Potential Mechanismsmentioning

confidence: 99%

Limited reversal of regional climate signals in overshoot scenarios

Pfleiderer,

Schleussner,

Sillmann

2024

Environ. Res.: Climate

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Without stringent reductions in emission of greenhouse gases in the coming years, an exceedance of the 1.5C temperature limit is increasingly likely. This has given rise to so-called temperature overshoot scenarios, in which the global mean surface air temperature exceeds a certain limit (i.e. 1.5C above pre- industrial levels) before bringing temperatures back below that limit. Despite their prominence in the climate mitigation literature, the implications of an overshoot for local climate impacts is still understudied. Here we present a comprehensive analysis of implications of an overshoot for regional temperature and precipitation changes as well as climate extremes indices. Based on a multi-model comparison from the Coupled Model Intercomparison Project (CMIP6) we find that temperature changes are largely reversible in many regions, but also report significant land-ocean and latitudinal differences after an overshoot. For precipitation, the emerging picture is less clear. In many regions the drying or wetting trend is continued throughout the overshoot irrespective of a change in the global mean temperature trend with resulting consequences for extreme precipitation. Taken together, our results indicate that even under a reversal of global mean temperature increase, regional climate changes may only be partially reversed in the decades after peak warming. We thus provide further evidence that overshooting of a warming level implies considerable risks on the regional level.

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Overturning Pathways Control AMOC Weakening in CMIP6 Models

Cited by 12 publications

References 88 publications

An uncertain future change in aridity over the tropics

An uncertain future change in aridity over the tropics

Controls on the Strength and Structure of the Atlantic Meridional Overturning Circulation in Climate Models

Limited reversal of regional climate signals in overshoot scenarios

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