Preprints
https://doi.org/10.5194/egusphere-2025-1784
https://doi.org/10.5194/egusphere-2025-1784
25 Apr 2025
 | 25 Apr 2025

Contribution of meridional overturning circulation and sea ice changes to large-scale temperature asymmetries in CMIP6 overshoot scenarios

Pedro José Roldán-Gómez, Pablo Ortega, and Markus G. Donat

Abstract. Analysis of overshoot scenarios, characterized by a peak in radiative forcing levels followed by a decline, show that changes during the CO2 increasing phase are not necessarily compensated during the CO2 decreasing phase, particularly at regional level. Even if the global mean temperature may recover after the overshoot, at the regional level the situation post-overshoot may differ from the situation pre-overshoot, with spatial patterns characterized by large-scale temperature asymmetries. These asymmetries, found between Northern (NH) and Southern Hemisphere (SH), between high and mid-latitudes of the NH, and between western and eastern areas of the Southern Ocean, alter atmospheric dynamics and through it the hydroclimate. Changes in the sea ice, changes in the ocean circulation and heat transport, and thermal inertia of the ocean have been identified as potential sources of hysteresis, highlighting the impact of oceanic changes in the behavior of atmospheric variables in case of overshoot. This work analyzes SSP5-3.4OS and SSP1-1.9 overshoot experiments from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to assess how well these mechanisms can explain the large-scale temperature asymmetries that characterize the difference between pre-overshoot and post-overshoot states. These analyses show that the relative contribution of each mechanism strongly depends on the model. Certain models like MRI-ESM2-0 are mainly impacted by changes in the Atlantic Meridional Overturning Circulation (AMOC), others like CNRM-ESM2-1 show a relevant impact of sea ice changes in high-latitude areas, and others like IPSL-CM6A-LR show also a relevant impact of changes in the Southern Meridional Overturning Circulation (SMOC). Inter-model differences in the contributions of the meridional overturning can be associated with different climatologies of Mixed Layer Depth (MLD) in the northern North Atlantic (NNA) and in certain areas of the Southern Ocean. Despite these differences across models, all the mechanisms contribute to shape the regional temperatures after overshoot, with the temperature asymmetries between NH and SH mainly explained by changes in the AMOC, those between high and mid-latitudes of the NH by sea ice changes, and those between western and eastern areas of the Southern Ocean by the SMOC. These results highlight the importance of model intercomparison and analysis of ocean dynamics to understand the regional impacts of an overshoot, and more generally the responses to forcing changes.

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Journal article(s) based on this preprint

07 Oct 2025
Contribution of meridional overturning circulation and sea ice changes to large-scale temperature asymmetries in CMIP6 overshoot scenarios
Pedro José Roldán-Gómez, Pablo Ortega, and Markus G. Donat
Ocean Sci., 21, 2283–2303, https://doi.org/10.5194/os-21-2283-2025,https://doi.org/10.5194/os-21-2283-2025, 2025
Short summary
Pedro José Roldán-Gómez, Pablo Ortega, and Markus G. Donat

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-1784', Anonymous Referee #1, 09 Jun 2025
    • AC1: 'Reply on RC1', Pedro Roldán, 17 Jul 2025
  • RC2: 'Comment on egusphere-2025-1784', Anonymous Referee #2, 16 Jun 2025
    • AC1: 'Reply on RC1', Pedro Roldán, 17 Jul 2025
  • EC1: 'Comment on egusphere-2025-1784', Meric Srokosz, 23 Jun 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-1784', Anonymous Referee #1, 09 Jun 2025
    • AC1: 'Reply on RC1', Pedro Roldán, 17 Jul 2025
  • RC2: 'Comment on egusphere-2025-1784', Anonymous Referee #2, 16 Jun 2025
    • AC1: 'Reply on RC1', Pedro Roldán, 17 Jul 2025
  • EC1: 'Comment on egusphere-2025-1784', Meric Srokosz, 23 Jun 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Pedro Roldán on behalf of the Authors (17 Jul 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (21 Jul 2025) by Meric Srokosz
RR by Anonymous Referee #2 (12 Aug 2025)
RR by Shouwei Li (26 Aug 2025)
ED: Publish subject to minor revisions (review by editor) (26 Aug 2025) by Meric Srokosz
AR by Pedro Roldán on behalf of the Authors (29 Aug 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (02 Sep 2025) by Meric Srokosz
AR by Pedro Roldán on behalf of the Authors (02 Sep 2025)

Journal article(s) based on this preprint

07 Oct 2025
Contribution of meridional overturning circulation and sea ice changes to large-scale temperature asymmetries in CMIP6 overshoot scenarios
Pedro José Roldán-Gómez, Pablo Ortega, and Markus G. Donat
Ocean Sci., 21, 2283–2303, https://doi.org/10.5194/os-21-2283-2025,https://doi.org/10.5194/os-21-2283-2025, 2025
Short summary
Pedro José Roldán-Gómez, Pablo Ortega, and Markus G. Donat
Pedro José Roldán-Gómez, Pablo Ortega, and Markus G. Donat

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Short summary
The overshoot scenarios, in which temperatures exceed the targets of the Paris Agreement and are brought back afterwards with a net-negative emission strategy, are known to activate irreversible processes in the climate system. This work analyses in detail the impact of some of these mechanisms, with a particular focus on those associated with ocean circulation and sea ice changes.
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