Wind amplifies the polar sea ice retreat

Ramdane Alkama,Ernest N Koffi,Giovanni Forzieri,Julienne Stroeve,Jennifer Ann Francis,Stephen J Vavrus,Timo Vihma,Alessandro Cescatti,Thomas Diehl

doi:10.1088/1748-9326/abc379

Abstract

The rapid polar sea ice retreat and its drivers are challenging and still unresolved questions in climate change research. In particular, the relationship between near-surface wind speed and sea ice extent remains unclear for two main reasons: (1) observed wind speeds over Polar Regions are very sparse, and (2) simulated winds by climate models are dependent on subjective parameterizations of boundary layer stratification, ultimately leading to large uncertainty. Here, we use observation-based data (passive microwave sea ice concentration and six different reanalysis datasets) together with output from 26 climate models (from the CMIP5 archive) to quantify the relationships between near-surface wind speed and sea ice concentration over the past 40 years. We find strong inverse relationships between near-surface wind speed and sea ice concentration that are consistent among the six reanalysis datasets. The poleward wind component is particularly increasing in years of reduced sea ice concentration, which contributes to the enhancement of the atmospheric (surface oceanic) poleward heat flux by up to 24 ± 1% (29 ± 2%) in the Arctic and 37 ± 3% (51 ± 3%) in the Antarctic seas, therefore boosting the impact of polar sea ice loss and contributing to polar amplification of climate warming. In addition, our results show a marginal contribution of the dynamical (pushing/opening/compacting) effects of wind on sea ice compared to the thermodynamic effects which in turn play a lower role than the associated change in local surface Autumn–Winter turbulent and Spring–Summer radiative fluxes. Climate models generally produce similar results but with lower magnitude, and one model even simulates the opposite relationship wind/sea-ice. Given the rapid changes in polar climate and the potential impacts on the mid-latitudes, it is urgent that model developments make use of evidence from satellite observations and reanalysis datasets to reduce uncertainties in the representation of relationships between polar winds and sea ice.

Highlights

Polar regions, especially the Arctic, are warming at least twice as fast as the global average (Blunden et al 2012), a feature called polar amplification
The poleward wind component is increasing in years of reduced sea ice concentration, which contributes to the enhancement of the atmospheric poleward heat flux by up to 24 ± 1% (29 ± 2%) in the Arctic and 37 ± 3% (51 ± 3%) in the Antarctic seas, boosting the impact of polar sea ice loss and contributing to polar amplification of climate warming
In order to investigate the causality in the observed processes we address the following two questions and hypotheses: 1. Is the monthly variability in polar wind driven by variability in sea ice concentration (SIC)? The hypothesis is that a strong reduction of the sea ice area and thickness in all seasons may lead to a substantial thermodynamic influence on the overlying atmosphere due to the sharp increase in surface temperature

Summary

Introduction

Especially the Arctic, are warming at least twice as fast as the global average (Blunden et al 2012), a feature called polar amplification. Sea ice cover change may affect atmospheric and ocean circulations, which in turn may contribute to polar amplification (Vihma 2014) This does not exclude totally the role of albedo feedback that can warm the Polar Ocean in the warm seasons and this can be communicated to the cold season by a reduction in winter sea ice cover which allows the relatively warm ocean to rapidly heat the overlying cold atmosphere. The relevance of these processes goes well beyond the polar zones, since sea ice decline contributes to the amplification of warming in the polar regions and may affect the entire climate system (Cohen et al 2014, England et al 2020): rising sea levels with its possible impact on ocean and sea shores (Nicholls and Cazenave 2010), changes in climate and precipitation patterns (Dore 2005), increase of the frequency and intensity of severe weather events (Stott 2016), and its impact on birds, marine mammals and polar bears (Stirling 1997, Smetacek and Nicol 2005)

Objectives

Methods

Results

Conclusion