Now new research suggests that the situation is especially dire because the ice sheets of Greenland are exposed to both rising air temperatures and the warming of the ocean waters with the former amplifying the effects of the latter.
“[T]hrough the release of ice sheet surface meltwater into the ocean, which excites near-glacier ocean circulation and in turn the transfer of heat from ocean to ice, a warming atmosphere can increase submarine melting even in the absence of ocean warming,” note scientists behind a study published in the journal Nature GeoScience.
The researchers, who are from the University of Edinburgh in Scotland and the University of California, San Diego, in the United States, reconstructed the rate of underwater melting at Greenland’s marine-terminating glaciers between 1979 and 2018 to estimate the resulting loss in ice in the sheet, which covers more than 650,000 square miles in all.
They have concluded that in the southern part of Greenland “variability in submarine melting was indeed governed by the ocean, but, in contrast, the atmosphere dominated in the northwest,” as they put it.
“At the ice sheet scale, the atmosphere plays a first-order role in controlling submarine melting and the subsequent dynamic mass loss. Our results challenge the attribution of dynamic mass loss to ocean warming alone and show that a warming atmosphere has amplified the impact of the ocean on the Greenland ice sheet,” the scientists explain.
In simple terms, the process is analogous to ice cubes melting faster when they are placed in a drink being stirred because the combination of warmer liquid and movement both have their impacts on melting the cubes.
“In Greenland, amplification occurs when warm air temperatures melt the surface of the ice sheet, generating meltwater. Meltwater flowing into the ocean creates turbulence that results in more heat melting the edges of the ice sheet submerged in the ocean [in] so-called submarine melting,” they elucidate.
Rising air temperatures have had an impact almost as marked as rising ocean temperatures on underwater melting, although the effect was not observed at the same rate in various regions around Greenland. While ocean temperature is the main factor behind the melting of ice underwater in south and central-west Greenland, atmospheric warming is equally damaging in the island’s northwest.
The edges of the Greenland ice sheet melt faster when the ocean is warmer and because rising air temperatures effectively result in a stirring of the ocean close to the ice sheet, this causes faster melting of the ice sheet by the ocean.
“This unfortunately adds to the overwhelming body of evidence showing the sensitivity of the Greenland ice sheet to climate change, hence the need for urgent action to reduce greenhouse gas emissions,” notes Donald Slater, a scientist at the University of Edinburgh’s School of GeoSciences who led the research.
“The findings suggest that if the atmosphere had not warmed since 1979, the retreat of Greenland’s glaciers, driven by submarine melting, could have been reduced by a half in the northwest region, and by a third across Greenland as a whole,” the scientists conclude.