Arctic permafrost response to an extreme sea ice loss event in the CESM2-WACCM climate model

Details

Supervisors

Massonnet, François ; Fichefet, Thierry

Faculty

Faculté des sciences

Degree label

Master [120] en sciences géographiques, orientation climatologie, à finalité approfondie

Abstract

The Arctic, where observed surface air temperatures have been warming nearly four times faster than the global average since 1979, is undergoing rapid transformations with profound environmental and socio-economic implications. This study examines the impacts of a major Rapid Sea Ice Loss Event (RILE) on Arctic permafrost using the CESM2-WACCM climate model under a high greenhouse gas emission scenario (SSP5-8.5). The simulated extreme RILE, characterized by a sea ice extent reduction of approximately 5 million square kilometers from 2031 to 2043, amplifies Arctic permafrost warming. Locally, permafrost temperature anomalies rise by up to 4°C per decade during winter at shallow depths, with an average winter warming rate that is three times faster than the climatological mean during the RILE period across Arctic permafrost regions (60–90°N). The warming signal penetrates to depths of about 10 meters, albeit with reduced intensity. The Nunavut, Chukotka, and Kara Sea regions are the most affected. Changes in active layer thickness (ALT) and the depth of zero annual temperature amplitude (Dzaa) reveal distinct responses between warm and cold permafrost. Warm permafrost margins exhibit ALT increases exceeding 4 meters per decade, while colder permafrost regions show Dzaa increases of up to 20 meters per decade. However, some areas experience decreases in both ALT and Dzaa. The permafrost response is driven by enhanced winter turbulent heat fluxes from the ocean to the atmosphere, warming adjacent lands. Additionally, atmospheric circulation anomalies result in colder or warmer air advection over permafrost regions. During summer, decreased cloud cover in some areas leads to increased solar radiation absorption by the ground. Correlations between surface condition changes and shallow ground temperature changes indicate that snow depth is the primary factor influencing the permafrost response during winter. Snow depth trend anomalies show localized increases of up to 40 cm per decade, particularly in the Chukotka region, contributing to complex patterns of surface energy exchange. This study suggests that Arctic permafrost may be vulnerable to extreme climate forcing such as a RILE, offering insights into the mechanisms driving its degradation. These findings emphasize the need to address Arctic warming and its global climate feedbacks, including accelerated carbon release. Future research involving different models and scenarios would improve understanding of the potential permafrost response.