Thursday, February 16, 2006
Sea level changes associated with Greenland ice loss accelerating and likely higher than previous estimates
Science published a report today from Rignot and Kanagaratnam indicating that Greenland's mass loss has doubled during the last decade. Due to previously unaccounted for ice dynamics, Greenland's ice loss will cause more sea level change than previously expected. Greenland Ice The study concludes:
Greenland's mass loss therefore doubled in the last decade, well beyond error bounds. Its contribution to sea-level rise increased from 0.23 ± 0.08 mm/year in 1996 to 0.57 ± 0.1 mm/year in 2005. Two-thirds of the loss is caused by ice dynamics; the rest is due to enhanced runoff minus accumulation. Ice dynamics therefore dominates the contribution to sea-level rise from the Greenland Ice Sheet.
Glacier acceleration in the east probably resulted from climate warming. Temperature records at Angmassalik (65.6°N, 37.6°E) show a +3°C increase in yearly air temperature from 1981–1983 to 2003–2005. The processes that control the timing and magnitude of glacier changes are, however, not completely characterized and understood at present. Glacier accelerations have been related to enhanced surface meltwater production penetrating to the bed to lubricate its motion, and ice-shelf removal, ice-front retreat, and glacier ungrounding that reduce resistance to flow. The magnitude of the glacier response to changes in air temperature (surface melting) and ocean temperature (submarine melting at calving faces) also depends on the glacier-bed properties, geometry, and depth below sea level and the characteristics of the subglacial and englacial water-storage systems. Current models used to project the contribution to sea level from the Greenland Ice Sheet in a changing climate do not include such physical processes and hence do not account for the effect of glacier dynamics. As such, they only provide lower limits to the potential contribution of Greenland to sea-level rise. If more glaciers accelerate farther north, especially along the west coast, the mass loss from Greenland will continue to increase well above predictions.