|April 16, 2020|
Greenland ice sheet melts at near record rate in 2019
|Last year was one of the worst years on record for Greenland's ice sheet, which shrank by hundreds of billions of tonnes in a high-pressure environment brought on by unusually clear skies and warmer temperatures.|
A study released on Wednesday found that a record number of clear-skied days in 2019 meant that more sunlight hit the surface of the ice sheet, while yearly snowfall was also reduced.
These conditions were caused by oscillations in the fast-moving jet stream air current that also trapped heat over Europe.
The increased pressure lasted for 63 of the 92 summer days last year, compared with an average of 28 days between 1981 and 2019.
The ice sheet lost about 600 billion tonnes in 2019, melting at a near record rate and much faster than the average of previous decades.
While 2019 saw the second-highest runoff from melting ice after 2012, it brought the biggest drops in surface mass balance since records began in 1948.
Surface mass balance takes into account gains in the ice sheet's mass, such as through snowfall, and losses from surface runoff of melted ice.
The study used satellite data, ground measurements and climate models to analyse changes in the ice sheet.
Lead author Marco Tedesco, from Columbia University's Lamont-Doherty Earth Observatory, warned that most climate models do not account for these atmospheric patterns, meaning that they are probably underestimating the impacts of global warming.
"You can see the mass balance in Greenland as your bank account," Mr Tedesco said.
"In some periods you spend more, and in some periods you earn more. If you spend too much you go negative.
"This is what happened to Greenland recently. These atmospheric conditions are becoming more and more frequent over the past few decades.
"It is very likely that this is due to the waviness of the jet stream, which we think is related to, among other things, the disappearance of snow cover in Siberia, the disappearance of sea ice, and the difference in the rate at which temperature is increasing in the Arctic versus the mid-latitudes."
The Greenland ice sheet contains enough frozen water to raise sea levels by as much as 7 metres.
Understanding the effects of atmospheric circulation changes will be crucial for improving projections of how much of that water will flood the oceans in the future, Mr Tedesco said.
The ice sheet, the second largest in the world, covers 1.71 million square kilometres, or about 94 per cent of Greenland's surface.