A sea ice free Arctic: Assessment Fast Track abrupt-127k experimental protocol and motivation [in review]

Sime, Louise C. ORCID: https://orcid.org/0000-0002-9093-7926; Diamond, Rachel ORCID: https://orcid.org/0009-0007-9071-139X; Stepanek, Christian ORCID: https://orcid.org/0000-0002-3912-6271; Brierley, Chris ORCID: https://orcid.org/0000-0002-9195-6731; Schroeder, David; Kageyama, Masa; Malmierca-Vallet, Irene ORCID: https://orcid.org/0000-0002-2871-9741; Blockley, Ed ORCID: https://orcid.org/0000-0002-0489-4238; West, Alex ORCID: https://orcid.org/0000-0002-9818-6848; Feltham, Danny; Ridley, Jeff; Braconnot, Pascale ORCID: https://orcid.org/0000-0002-1852-9178; Williams, Charles J. R. ORCID: https://orcid.org/0000-0003-1791-2463; Shi, Xiaoxu; Otto-Bliesner, Bette L. ORCID: https://orcid.org/0000-0003-1911-1598; Macarewich, Sophia I.; Ramos Buarque, Silvana ORCID: https://orcid.org/0000-0001-5687-1460; Zhang, Qiong ORCID: https://orcid.org/0000-0002-9137-2883; LeGrande, Allegra; Zheng, Weipeng ORCID: https://orcid.org/0000-0003-1968-197X; Jiang, Dabang ORCID: https://orcid.org/0000-0003-0756-0169; Morozova, Polina; Guo, Chuncheng ORCID: https://orcid.org/0000-0001-6276-6499; Zhang, Zhongshi; Yeung, Nicholas ORCID: https://orcid.org/0000-0002-6560-6658; Menviel, Laurie ORCID: https://orcid.org/0000-0002-5068-1591; Narayanasetti, Sandeep; Reeves, Olivia; Pollock, Matthew; Zhao, Anni ORCID: https://orcid.org/0000-0001-5119-7454. 2025 A sea ice free Arctic: Assessment Fast Track abrupt-127k experimental protocol and motivation [in review]. EGUsphere [preprint]. 10.5194/egusphere-2025-3531

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Abstract/Summary

Given that the Arctic could be ice-free in summer within the next ten to twenty years, accurately predicting low-ice states is of crucial importance. Paleo-evidence shows that the strong orbitally-induced high latitude insolation anomaly at 127,000 years ago (127 ky), of around +70 W m−2 in the Arctic during spring-summer, led to warm conditions and an Arctic that was occasionally or often ice-free during summer. Building on two Coupled Model Intercomparison Projects (CMIPs): the Sea-Ice Model Intercomparison Project and the Paleoclimate Modelling Intercomparison Project, we propose an Assessment Fast Track experiment, abrupt-127k, focusing on this seasonally ice-free, or near ice-free, Arctic at 127 ky. The abrupt-127k experiment is initialised from a piControl simulation and abruptly imposes observed values for the insolation distribution and greenhouse gas forcing at 127 ky. It provides a new opportunity to evaluate models used to compute climate projections, both against paleo-evidence and each other, during a known low Arctic sea ice state. As CMIP models are not usually tuned to paleo observations, abrupt-127k represents a true ‘out-of-sample’ test. The abrupt-127k experiment has four key scientific objectives, to: ascertain the simulated Arctic sea ice state, including the presence and characteristics of last-ice areas; evaluate the simulated climates using Arctic paleo-evidence; characterise the central Arctic surface energy budget; and analyse the ice budget including ice melt, growth, and transport. We show that a large Arctic ice response will manifest within the first 30 years of the simulation, thus a single 100-year long run is sufficient for these objectives. Modelling groups are requested to follow standard CMIP output protocol for analysis, including the use of standard ‘fixed-length’ output. Given Fast Track abrupt- 127k is similar in setup to abrupt-2xCO2 and abrupt-4xCO2 experiments, combined analysis of these abrupt-experiments will facilitate understanding of the impacts of instantaneous radiative forcing in the Arctic.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.5194/egusphere-2025-3531
Date made live:	25 Sep 2025 08:04 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/540282

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