About 80 percent of the ice sheet’s surface is like a snowcone: A dusting of fresh snowfall covers a thick layer of old snow, called firn, that’s slowly being compressed into glacier ice but still contains plenty of air pockets. When the top of this snow cone melts in the summer, liquid water percolates down into the firn, which soaks it up like a 100-foot-thick sponge.

…They started finding dense, compacted layers of ice in core after core, just below the seasonal snow layer. It was, MacFerrin says, as if a “turtle shell” had formed over the firn.

…That summer, for the first time on record, meltwater from this part of Greenland visibly started to flow away as runoff.

…Ice slabs have already caused Greenland’s runoff zone to expand by about 26 percent, according to the new study. 

…Under a worst-case scenario where carbon emissions continue to climb until the end of the century, the researchers calculated that ice slab proliferation could add up to 3 inches of sea level rise by 2100, boosting the ice sheet’s overall sea level rise contribution by nearly a third. In both a middle-of-the-road scenario where emissions peak by mid-century and the high emissions one, the amount of runoff from Greenland’s interior roughly doubles by century’s end.

…“We have never observed an ice sheet behaving this way before,” Poinar says. “It’s unprecedented in human scientific history.”

As Greenland melts, something strange is happening to the ice sheet

sigh….