Hidden slabs of frozen meltwater have grown rapidly beneath Greenland’s snowy surface since 2001, scientists say. And these ice slabs are amping up the ice sheet’s contribution to rising seas.
By forcing more meltwater to run along the surface and pour directly into the sea, the impermeable slabs could increase Greenland’s contribution to global sea level rise from seven to 74 millimeters by 2100, depending on future greenhouse gas emissions, simulations suggest. So far, additional meltwater runoff due to the slabs has contributed about one millimeter to global sea levels, researchers report in the Sept. 19 Nature.
Greenland’s melting, set off by global warming due to higher levels of carbon dioxide and other greenhouse gases in the atmosphere, has increased dramatically in the last few decades. Since 1972, the island has contributed about 14 millimeters to sea level rise, but much of that melting occurred after the turn of the century.
Record-breaking summertime melting occurred in 2002, 2007, 2012 and most recently, 2019, says Michael MacFerrin, a glaciologist at the University of Colorado Boulder (SN: 8/2/19). Some of that meltwater refreezes in the wintertime, forming thick, impermeable layers of ice around Greenland’s perimeter that can stretch for tens of kilometers, MacFerrin and colleagues say. The team dubbed the layers “ice slabs” in their new study.