How is the Greenland ice sheet behaving under global warming and what are the potential impacts of ice mass loss?

Meg Stewart June 5, 2015

Outline

o Background on the Greenland Ice Sheet (GrIS)o Processes resulting in ice mass losso Proposed mechanism for GrIS mass loss

Subpolar location in the northern hemisphere

Ice sheets and glaciers are considered among the most sensitive indicators of climate change

Loss of ice mass believed to be due to 1) submarine melting, and 2) inflow of subtropical waters

Strong seasonal variations – with greater ice mass decreases observed in the summers

Background

Source: PfefferSource: Pfeffer (2011)

Background

Gravity is determined by mass. By measuring gravity anomalies, GRACE shows how mass is distributed around the planet and how it varies over time.

GRACE has been collecting gravity anomaly data since March 2002.

Gravity Recovery and Climate Experiment

or GRACE

Figure 1 - Greenland

Source: Velicogna (2009)

Greenland ice sheet losing mass at an accelerated rate

From 1992 to 2011 Greenland has lost twice the ice mass as the Antarctic ice sheet (Shepherd, et al. 2013)

Cumulative sea level rise (1989–2009)

Source: Van den Broeke, Bamber, Lenaerts & Rignot (2011)

Greenland Ice Sheet

Antarctic Ice Sheet

Total

Source: Harig, Christopher & Simons, Frederik J. (2012)

Where, Total mass balance =

surface mass balance – discharge

1) negative surface mass balance is attributed to a persistent increase in surface melt in southeast and west Greenland.

Processes resulting in ice mass loss

2) Increased ice discharge resulting from the speed up, thinning and retreat of multiple marine terminating glaciers (in contrast to those terminating on land).

Processes resulting in ice mass loss

Helheim Glacier that terminates into Sermilik Fjord in southeast Greenland. Source: Straneo & Heimbach (2013)

External forcings: changes in precipitation on the ice sheet and rising air temperatures increasing surface melting

Change in sea surface temperatures around Greenland have correlated to changes in coastal air temperatures and changes in runoff

Ocean forcing is also a potential driver of changes in the ice mélange

The mechanisms and forcings behind the increased ice discharge, however, remain elusive.

Ice-sheet-ocean interactions occurring at two scales

Warm, ocean waters from the south and Cold, fresh water from the Arctic flows around Greenland’s deep continental shelf.

Source: Straneo & Heimbach (2013)

Proposed mechanism

Cold water from the north; warm water from the south (subtropics).

Source: Straneo & Heimbach (2013)

Proposed mechanism

Source: Straneo & Heimbach (2013)

Cold water and warm water resists mixing

The warmer water works on melting the glacier, producing subglacial discharge

Buoyancy driven circulation

Proposed mechanism

Concluding thoughts

o Responses to climate change require a cross-disciplinary focus

o International collaborationo Modeling from all disciplinary fieldso New instruments on the ground, at sea and in spaceo Rigorous efforts to synthesize the heterogeneous data

streams into a coherent, sustainable and dynamic network.

Full understanding of the Greenland Ice Sheet is complicated by a relative lack of high-quality data. A concerted effort is required to reduce the uncertainty in projected contributions to sea-level rise.

References

o Harig, C. & Simons, F. J. (2012) Mapping Greenland’s mass loss in space and time. Proceedings of the National Academy of Sciences. 109 (49), 19934–19937.

o Pfeffer, W.T. (2011). Land ice and sea level rise: A thirty-year perspective. Oceanography. 24(2):94–111.

o Straneo, F. & Heimbach, P. (2013). North Atlantic warming and the retreat of Greenland’s outlet glaciers. Nature. 504, 36.

o van den Broeke, M. R., Bamber, J. L., Lenaerts & Rignot, E. (2011). Ice Sheets and Sea Level: Thinking Outside the Box. Survey Geophysics. 32, 495–505.

o Velicogna, I. (2009). Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE. Geophysical Research Letters. 36, L19503.