Buffer effect of Greenland’s firn could cease around 2130
New projections under high warming scenarios
Increasing melt threatens to saturate the firn layer that covers the Greenland ice sheet. Saturation of this layer will dramatically increase global sea level rise, adding about 9 mm a year from the Greenland ice sheet alone (the current sea level rise from all sources is about 4 mm per year). A new study by researchers from Utrecht University, the US National Center for Atmospheric Research, and University of Colorado Boulder now shows that this threshold could be reached as early as the first half of the 22nd century. The findings were published online this weekend in the journal Nature Communications.
Over 90 percent of the Greenland ice sheet is covered by an up to hundred meters thick, porous layer of compressed snow, called firn. “This layer full of air pockets can be seen as a sponge.” says Brice Noël, lead author of the paper. In summer, meltwater infiltrates the air pockets. During the cold Arctic winter, the meltwater in the pockets refreezes, and does not leave the ice sheet. Today this happens to about half of the surface melt, the remainder runs off to the ocean.
The mass loss from the Greenland ice sheet would accelerate and result in a global sea level rise of about 9 mm each year
However, when melt increases due to climate change, the firn layer could start to saturate, reducing and eventually completely removing the buffer effect. “Once soaked, a sponge cannot absorb any more water. This also applies to saturated firn.” Noël adds: “As a consequence, all additional meltwater will run off into the ocean. The mass loss from the Greenland ice sheet would accelerate and result in a global sea level rise of about 9 mm each year. This represents an over 20-fold increase relative to the ice sheet average contribution since 1992.”
The year 2130
Under high warming scenarios this refreezing potential will reach a peak around the year 2130, the study shows. Under intermediate warming scenarios, this will occur about half a century later. Under low warming scenarios, the threshold will not be reached. The researchers used climate models to project this evolution of the Greenland firn layer. Until the mid-1990s the refreezing potential of firn remained steady, but following atmospheric warming, it started to increase thereafter.