The Greenland Ice Sheet is accelerating in its slide into the ocean, like snow sliding off a roof on a sunny day.
According to the University of Colorado Boulder, massive releases of meltwater from surface lakes are speeding up sea level rise.
During summer, meltwater pools into lakes on the ice sheet's surface. When the water pressure gets high enough, the ice fractures beneath the lake, and a huge burst of water plummets through to the bed of the ice sheet.
"This is the first evidence that Greenland's supraglacial lakes have responded to recent increases in surface meltwater production by draining more frequently, as opposed to growing in size," says William Colgan, of the university's Cooperative Institute for Research in Environmental Sciences (CIRES).
The researchers used satellite images along with new feature-recognition software to monitor nearly 1,000 lakes over a 10-year period. They discovered that as the climate warms, such catastrophic drainages are increasing in frequency, being 3.5 times more likely to occur during the warmest years than the coldest.
During such drainages, about a million cubic meters of meltwater funnels to the ice sheet's underside within a couple of days. Once there, it lubricates the ice sheet's glide into the ocean.
On other occasions, though, such drainages may actually decrease the slide of the ice sheet, by carving out sub-glacial 'sewers' to efficiently route water to the ocean.
"Lake drainages are a wild card in terms of whether they enhance or decrease the ice sheet's slide," says CIRES research associate William Colgan. As usual, more research is required.