West Antarctic Ice Sheet retreat in the context of ENSO variability

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Satellite observations show rapid changes in the rate of ice loss from West Antarctica, but attribution of their cause is uncertain and requires modelling of the full ice-ocean system. Recent studies highlight the influence of El Niño Southern Oscillation (ENSO) on this important contribution to sea level. The hypothesised mechanism is through changes in ice-shelf melting, attributed to wind-forced variation in the depth of the oceanic thermocline that separates cooler surface waters from warmer Circumpolar Deep Water beneath. To improve upon detailed forecasts of West Antarctic ice using steady climate forcing, we propose novel experiments using a new synchronously coupled ice/ocean model that can continuously compute the response of the ice sheet to highly-variable oceanic forcing driven by ENSO. We seek to quantify: (1) the probability that 20th Century retreat of West Antarctic ice was triggered by ENSO; (2) the probability that sequential strong La Niña events could halt the retreat happening now; (3) formal attribution of changes in the West Antarctic Ice Sheet to ENSO or anthropogenic trends in zonal winds; and (4) the impact of ENSO and anthropogenic trends on predicted extremes of 21st Century sea level used for coastal planning decisions.