Ice slabs (metres-thick, low-permeability ice) in Greenland have increased the ice sheet’s total meltwater runoff area by around 26% since 2001, reports a paper in Nature. As ice slabs continue to expand, the study suggests that the additional area of meltwater runoff could contribute 7 - 74 mm to global sea-level rise by 2100 under different emissions scenarios.
Ice slabs are layers of ice (at least one metre thick) that form over multiple years when meltwater refreezes between existing ice layers. They can span tens of kilometres and their low permeability means that surface meltwater from the ice sheet is not reabsorbed by porous snow (which can act as a buffer to sea-level rise).
Michael MacFerrin and colleagues set out to quantify the formation of ice slabs and predict their growth and its potential effect on meltwater runoff under moderate- and high-emissions scenarios (greenhouse gas emissions peaking by 2040 or continuing to rise through the 21st century, respectively). The authors find that as of the end of 2013, ice slabs cover an additional 62,100-78,900 km2 compared to Greenland’s runoff area before 1990. Under both scenarios, their model predicts that the area covered by ice slabs will approximately double by 2050, and by 2100 the volume of meltwater runoff from areas covered by ice slabs will be double the estimated runoff for a scenario without ice slabs.
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