Greenland water runoff may intensify

A team of international scientists has found evidence that changing conditions in Greenland’s ice cap may be reducing the capacity of a layer of granular snow near the ice cap surface to hold meltwater, thus increasing the runoff of the water, according to a paper published in the Jan. 4 issue of Nature Climate Change. Although ice melts at the surface of the ice cap, a significant portion of that water can refreeze inside the porous near-surface layer of granular snow, thus limiting the impact of the ice melt on sea level rise, the paper says. But in situ observations and historic data demonstrate that surface runoff begins to dominate meltwater storage before the available pore space becomes completely filled.

With two exceptional melt summers in 2010 and 2012, successive intensive melts have caused structural changes in the granular snow layer. At elevations above about 1,000 meters, the material has become denser, while at lower elevations, where melt has been most intense, the porous layer has lost most of its ability to retain meltwater, the paper says. At the lower elevations, the formation of near-surface ice layers has rendered the deeper porous space difficult to access, forcing meltwater into a surface discharge system and intensifying ice-sheet mass loss earlier than previously thought, the paper says.

- ALAN BAILEY