Quantifying `missing melt' in regional climate model predictions of Greenland ice sheet change
Abstract
Since 2010, the rate of mass loss from Greenland has increased and the ice sheet has experienced more episodes of rare and extreme surface melt. In addition to directly removing more of the ice sheet into the sea, extreme melt events reduce the reflectivity of the ice sheet and can warm the perennial snow pack through latent heat release when the melt water refreezes, both of which act as a positive feedback to further enhance melt. As such, an understanding of the frequency, duration and magnitude of extreme melt events is necessary to constrain predictions of future ice sheet state. Melting on Greenland is typically predicted using Regional Climate Models (RCM), however, although RCMs are excellent at reproducing 'normal' conditions (low amplitude/frequency signals) and long term trends, they may not resolve unusually high/low magnitude features, particularly of either small spatial scale or short temporal duration. Extreme melt events for example, typically only last for a day or so and thus their effects are likely omitted from RCM estimates of future ice sheet change. Here, we present a new climatology of historic extreme melt events on Greenland, diagnosed using tools from Extreme Value Theory Statistics. We use these data to evaluate the ability of the MAR (Modele Atmospherique Regional) RCM to reproduce the frequency, magnitude and duration of extreme melt events in the past, with forcing by both re-analysis (ERA-Interim) and GCM (CMIP5) predictions at the model boundaries. By modelling the relationship between MAR predicted values, and observations, we are able to estimate the degree to which MAR over/under estimates melting due to the omission of extreme events for a given boundary forcing. We use this relationship together with MAR predictions of future change to quantify the likely amount of `missing melt' in MAR-based projections of global sea level rise due to these short term, high magnitude perturbations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.C41E0714L
- Keywords:
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- 0762 Mass balance 0764 Energy balance;
- CRYOSPHEREDE: 0794 Instruments and techniques;
- CRYOSPHEREDE: 0798 Modeling;
- CRYOSPHERE