Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat

Michalea D King,Brice P Y Noël,Myoung J Noh,Ian M Howat,Bert Wouters,Salvatore G Candela,Michiel R Van Den Broeke,Adelaide Negrete,Seongsu Jeong

doi:10.1038/s43247-020-0001-2

Michalea D King, Brice P Y Noël + Show 7 more

Open Access

https://doi.org/10.1038/s43247-020-0001-2

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Abstract

The Greenland Ice Sheet is losing mass at accelerated rates in the 21st century, making it the largest single contributor to rising sea levels. Faster flow of outlet glaciers has substantially contributed to this loss, with the cause of speedup, and potential for future change, uncertain. Here we combine more than three decades of remotely sensed observational products of outlet glacier velocity, elevation, and front position changes over the full ice sheet. We compare decadal variability in discharge and calving front position and find that increased glacier discharge was due almost entirely to the retreat of glacier fronts, rather than inland ice sheet processes, with a remarkably consistent speedup of 4–5% per km of retreat across the ice sheet. We show that widespread retreat between 2000 and 2005 resulted in a step-increase in discharge and a switch to a new dynamic state of sustained mass loss that would persist even under a decline in surface melt.

Highlights

The Greenland Ice Sheet is losing mass at accelerated rates in the 21st century, making it the largest single contributor to rising sea levels
To account for the uncertainty in D due to this temporal gap in ice thickness observations, we estimate D assuming the end member-cases of (1) all thickness change occurring in the first year, which maximizes the impact of thinning at the start of the period, and (2) all thinning occurring in the last year, which minimizes the impact until ~2000
We estimate over three decades of Greenland Ice Sheet (GrIS)-wide ice discharge at high temporal resolution and with well-defined uncertainties, capturing a rapid, step-increase between two distinct states of discharge, and reaching an annual maximum of ~500 Gt yr−1 in 2017 and 2018

Summary

Introduction

The Greenland Ice Sheet is losing mass at accelerated rates in the 21st century, making it the largest single contributor to rising sea levels. The Greenland Ice Sheet (GrIS) has been losing mass for several decades[1] due to both increased surface meltwater runoff and ablation of marine-terminating outlet glaciers via calving and submarine melting, termed ice discharge. Widespread glacier retreat explains most (>90%) of the observed multi-decadal variability in discharge, with a observed increase in discharge of 4–5% per every weighted mean kilometer of retreat. We find that this sensitivity is proportionally consistent across different regions of the ice sheet, despite highly variable long-term trends in discharge. Following the step-increase in discharge, GrIS-wide totals have remained relatively stable at rates near 495–500 Gt yr−1, reflecting an increase that was sufficient to effectively shift the ice sheet to a state of persistent mass loss

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