Articles | Volume 10, issue 5
The Cryosphere, 10, 1933–1946, 2016

Special issue: Mass balance of the Greenland Ice Sheet

The Cryosphere, 10, 1933–1946, 2016

Research article 06 Sep 2016

Research article | 06 Sep 2016

On the recent contribution of the Greenland ice sheet to sea level change

Michiel R. van den Broeke1, Ellyn M. Enderlin2, Ian M. Howat3, Peter Kuipers Munneke1, Brice P. Y. Noël1, Willem Jan van de Berg1, Erik van Meijgaard4, and Bert Wouters1 Michiel R. van den Broeke et al.
  • 1Institute for Marine and Atmospheric Research Utrecht, Utrecht University, the Netherlands
  • 2Climate Change Institute and School of Earth and Climate Sciences, University of Maine, USA
  • 3School of Earth Sciences and Byrd Polar and Climate Research Center, Ohio State University, USA
  • 4Royal Netherlands Meteorological Institute, De Bilt, the Netherlands

Abstract. We assess the recent contribution of the Greenland ice sheet (GrIS) to sea level change. We use the mass budget method, which quantifies ice sheet mass balance (MB) as the difference between surface mass balance (SMB) and solid ice discharge across the grounding line (D). A comparison with independent gravity change observations from GRACE shows good agreement for the overlapping period 2002–2015, giving confidence in the partitioning of recent GrIS mass changes. The estimated 1995 value of D and the 1958–1995 average value of SMB are similar at 411 and 418 Gt yr−1, respectively, suggesting that ice flow in the mid-1990s was well adjusted to the average annual mass input, reminiscent of an ice sheet in approximate balance. Starting in the early to mid-1990s, SMB decreased while D increased, leading to quasi-persistent negative MB. About 60 % of the associated mass loss since 1991 is caused by changes in SMB and the remainder by D. The decrease in SMB is fully driven by an increase in surface melt and subsequent meltwater runoff, which is slightly compensated by a small ( <  3 %) increase in snowfall. The excess runoff originates from low-lying ( <  2000 m a.s.l.) parts of the ice sheet; higher up, increased refreezing prevents runoff of meltwater from occurring, at the expense of increased firn temperatures and depleted pore space. With a 1991–2015 average annual mass loss of  ∼  0.47 ± 0.23 mm sea level equivalent (SLE) and a peak contribution of 1.2 mm SLE in 2012, the GrIS has recently become a major source of global mean sea level rise.

Short summary
We present recent (1958–2015) mass balance time series for the Greenland ice sheet. We show that recent mass loss is caused by a combination of increased surface meltwater runoff and solid ice discharge. Most meltwater above 2000 m a.s.l. refreezes in the cold firn and does not leave the ice sheet, but this goes at the expense of firn heating and densifying. In spite of a temporary rebound in 2013, it appears that the ice sheet remains in a state of persistent mass loss.