Constraining the First Year of Ice-Free Arctic: Importance of Regional Perspective

Abstract

The ice-free Arctic in summer not only symbolizes human-induced climate change but also highlights the need to critically consider climate change adaptation policies. To constrain projections when the Arctic Ocean will first become ice-free, studies have typically combined the historical observations of the Arctic sea ice area (SIA) with future emission scenario simulations. However, these studies primarily relied on the historical climatology and trend of the Arctic SIA, without considering regional variations. In this study, we analyze September SIA projections using the Coupled Model Intercomparison Project Phase 6 (CMIP6) model simulations, while considering Arctic sub-regions. Additionally, we assess the impact of incorporating sub-region September SIA when constraining the first year of ice-free Arctic in September. CMIP6 models generally overestimate the historical September SIA decreasing trend in the central Arctic, whereas they underestimate this trend in the surrounding shelf seas. The central Arctic, where the region expected to retain sea ice for the longest period in the future, holds particular significance for projecting when the Arctic will first become ice-free. Consequently, when we employ the historical trend of September SIA in the central Arctic as a constraint, observationally-constrained projections suggest a delay of 12 years (2056) for the first ice-free September compared to raw/unconstrained projections (2044 in model average) under a high-emission scenario. These findings underscore the importance of considering model biases in central Arctic SIA when constraining projections of the first year of ice-free Arctic, which may occur later than previously projected in many studies.