TY - JOUR
T1 - A sea ice free Arctic
T2 - CMIP7 Assessment Fast Track abrupt-127k experimental protocol and motivation
AU - Sime, Louise C.
AU - Diamond, Rachel
AU - Stepanek, Christian
AU - Brierley, Chris
AU - Schroeder, David
AU - Kageyama, Masa
AU - Pollock, Matthew
AU - Malmierca-Vallet, Irene
AU - Blockley, Ed
AU - West, Alex
AU - Feltham, Danny
AU - Ridley, Jeff
AU - Braconnot, Pascale
AU - Williams, Charles J.R.
AU - Shi, Xiaoxu
AU - Otto-Bliesner, Bette L.
AU - Macarewich, Sophia I.
AU - Ramos Buarque, Silvana
AU - Zhang, Qiong
AU - LeGrande, Allegra
AU - Zheng, Weipeng
AU - Jiang, Dabang
AU - Morozova, Polina
AU - Guo, Chuncheng
AU - Zhang, Zhongshi
AU - Yeung, Nicholas
AU - Menviel, Laurie
AU - Narayanasetti, Sandeep
AU - Yoshimori, Masakazu
AU - Reeves, Olivia
AU - Zhao, Anni
N1 - Publisher Copyright:
© 2026 Louise C. Sime et al.
PY - 2026/7/7
Y1 - 2026/7/7
N2 - Given that the Arctic could be ice-free in summer within the next ten to 20 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 Wm-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 abrupt-127k is similar in setup to abrupt-2xCO2 and abrupt-4xCO2 CMIP7 experiments, combined analysis of these abrupt-experiments will facilitate understanding of the impacts of instantaneous radiative forcing in the Arctic.
AB - Given that the Arctic could be ice-free in summer within the next ten to 20 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 Wm-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 abrupt-127k is similar in setup to abrupt-2xCO2 and abrupt-4xCO2 CMIP7 experiments, combined analysis of these abrupt-experiments will facilitate understanding of the impacts of instantaneous radiative forcing in the Arctic.
UR - https://www.scopus.com/pages/publications/105044248733
U2 - 10.5194/gmd-19-5881-2026
DO - 10.5194/gmd-19-5881-2026
M3 - Article
AN - SCOPUS:105044248733
SN - 1991-959X
VL - 19
SP - 5881
EP - 5905
JO - Geoscientific Model Development
JF - Geoscientific Model Development
IS - 13
ER -