Preprints
https://doi.org/10.5194/egusphere-2025-2039
https://doi.org/10.5194/egusphere-2025-2039
19 May 2025
 | 19 May 2025

Catalogue of Strong Nonlinear Surprises in ocean, sea-ice, and atmospheric variables in CMIP6

Joran R. Angevaare and Sybren S. Drijfhout

Abstract. The Coupled Model Intercomparison Project Phase 6 (CMIP6) archive was analysed for the occurrence of Strong Nonlinear Surprises (SNS) in future climate-change projections. To this end, we built an automated detection algorithm to identify SNS in a reproducible manner. Two different types of SNS were defined: abrupt changes measured over decadal timescales and slower state transitions, too large to be explained by the forcing without invoking strong internal feedbacks in the climate system. Data of 54 models were analysed for five shared socio-economic pathways for ocean, sea ice, and atmospheric variables. The algorithm isolates regions of at least 106 km2 and utilizes stringent criteria to select SNS. In total 73 SNS were found, divided in 11 categories of which 4 apply to abrupt change and 7 to state transitions. Of the identified SNS 45 % relate to sea-ice cover, 19 % to ocean currents, 29 % to mixed layer depth, and 7 % to atmospheric systems like the Intertropical Convergence Zone. For each category, probability density functions for time-windows of maximal change indicate SNS occurring earlier and at lower global temperature rise than assessed in previous reviews, in particular the ones associated with winter Arctic Sea ice disappearance, northern North Atlantic winter mixed layer collapse and subsequent transition of the Atlantic Meridional Overturning Circulation (AMOC) to a weak state in which the cell associated with North Atlantic Deep Water involved has vanished. This catalogue emphasizes the possibility of SNS already below 2 °C of global warming, even more than the previous assessments based on CMIP5 data.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
Share
Joran R. Angevaare and Sybren S. Drijfhout

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-2039', Anonymous Referee #1, 12 Jul 2025
  • RC2: 'Comment on egusphere-2025-2039', Anonymous Referee #2, 24 Sep 2025
Joran R. Angevaare and Sybren S. Drijfhout
Joran R. Angevaare and Sybren S. Drijfhout

Viewed

Total article views: 890 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
788 84 18 890 16 26
  • HTML: 788
  • PDF: 84
  • XML: 18
  • Total: 890
  • BibTeX: 16
  • EndNote: 26
Views and downloads (calculated since 19 May 2025)
Cumulative views and downloads (calculated since 19 May 2025)

Viewed (geographical distribution)

Total article views: 855 (including HTML, PDF, and XML) Thereof 855 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 27 Sep 2025
Download
Short summary
We presents a first overview of abrupt changes and state transitions in ocean, sea-ice, and atmospheric variables under future climate change scenarios in CMIP6 data. We find a surprisingly high number models that show Arctic Sea ice disappearance, northern North Atlantic winter mixed layer collapse and/or subsequent transition of the Atlantic Meridional Overturning Circulation to a very weak state. We find more abrupt changes than in previous work and often at lower global warming levels.
Share