Preprints
https://doi.org/10.5194/tc-2022-121
https://doi.org/10.5194/tc-2022-121
 
12 Jul 2022
12 Jul 2022
Status: this preprint is currently under review for the journal TC.

Anthropogenic and internal drivers of wind changes over the Amundsen Sea, West Antarctica, during the 20th and 21st centuries

Paul Holland1, Gemma O'Connor2, Thomas Bracegirdle1, Pierre Dutrieux1, Kaitlin Naughten1, Eric Steig2, David Schneider3,4, Adrian Jenkins5, and James Smith1 Paul Holland et al.
  • 1British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
  • 2University of Washington, Seattle, USA
  • 3National Center for Atmospheric Research, Boulder, USA
  • 4University of Colorado, Boulder, USA
  • 5Northumbria University, Newcastle, UK

Abstract. Ocean-driven ice loss from the West Antarctic Ice Sheet is a significant contributor to sea-level rise. Recent ocean variability in the Amundsen Sea sector is primarily controlled by near-surface winds. We combine paleoclimate reconstructions and climate model simulations to understand past and future influences on Amundsen Sea winds from anthropogenic forcing and internal climate variability. The reconstructions show strong historical wind trends. External forcing from greenhouse gases and stratospheric ozone depletion drove zonally-uniform westerly wind trends centred over the deep Southern Ocean. Internally-generated trends resemble a south Pacific Rossby wave train, and were highly influential over the Amundsen Sea continental shelf. There was strong interannual and interdecadal variability over the Amundsen Sea, with periods of anticyclonic wind anomalies in the 1940s and 1990s, when rapid ice loss was initiated. Similar anticyclonic anomalies probably occurred prior to the 20th century, but without causing the present ice loss. This suggests that ice loss may have been triggered naturally in the 1940s, but failed to recover subsequently due to the increasing importance of anthropogenic forcing from greenhouse gases (since the 1960s) and ozone depletion (since the 1980s). Future projections also feature strong wind trends. Emissions mitigation influences wind trends over the deep Southern Ocean but has less influence on winds over the Amundsen Sea shelf, where internal variability creates a large and irreducible uncertainty. This suggests that strong emissions mitigation is needed to minimise ice loss this century, but that the uncontrollable future influence of internal climate variability could be equally important.

Paul Holland et al.

Status: open (until 07 Sep 2022)

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Paul Holland et al.

Paul Holland et al.

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Short summary
The Antarctic Ice Sheet is losing ice, causing sea-level rise. However, it is not known whether human-induced climate change contributed to this ice loss. In this study, we use evidence from climate models and paleoclimate measurements (e.g. ice cores) to suggest that the ice loss was triggered by natural climate variations, but is now sustained by human-forced climate change. This implies that future greenhouse gas emissions may influence sea-level rise from Antarctica.