Greenland melting tied to shrinking Arctic sea ice

Shrinking Arctic sea ice during summers enhances the flow of warm, moist air over Greenland, increasing the extreme heat events and surface ice melting, a new study has found.

The dramatic trends of vanishing Arctic sea ice, dogged weather systems over Greenland, far-flung surface ice melting on the massive island, and global sea-level rise are linked, according to researchers, including Jennifer Francis from Rutgers University in US.

During Greenland summers, melting Arctic sea ice favours stronger and more frequent "blocking-high" pressure systems, which spin clockwise, stay largely in place and can block cold, dry Canadian air from reaching the island.

The highs tend to enhance the flow of warm, moist air over Greenland, contributing to increased extreme heat events and surface ice melting, according to the study.

That, in turn, fuels sea-level rise, said Francis, who called rising seas a "monstrous" issue for coastal communities around the world.

The increased melting on the Greenland ice sheet in recent years may also be linked to cooler-than-normal ocean temperatures south of the island, slowing ocean circulation.

The study tapped computer models and measurements in the field.

"I think this study does a good job of pinning down the fact that the Arctic sea ice is disappearing for a whole bunch of reasons - and that is causing the surface of Greenland's melt area to increase," Francis said.

The Greenland ice sheet holds an enormous volume of frozen water, and the global sea level would rise about 20 to 23 feet if it all melted, the study noted.

Surface melting of the ice sheet has increased dramatically since the relative stability and modest snow accumulation in the 1970s, researchers said.

Since 2009, most of the increased rate of Greenland ice loss has stemmed from greater surface melting, heightening concerns that sea level-rise could accelerate beyond most projections and boost threat levels for coastal communities, according to the study.

According to Francis, blocking-high pressure systems over Greenland usually form when a lot of warm air is in the Arctic.

So far this year, it has been extremely warm and Arctic sea ice has been at record low levels for this time of year.

The Arctic warmth tends to weaken the jet stream, which typically flows west to east, allowing it to meander more to the north and south, Francis said.

The jet stream can take "such a big northward swing that it actually kind of breaks off and forms a closed circulation," she said.

Blocking highs tend to be persistent and are hard to forecast, she added.

Both transport a lot of heat, moisture and clouds over the Greenland ice sheet, leading to more melting.

The study was published in the Journal of Climate.