Lack of fresh snowfall causes Greenland to melt faster

A lack of fresh snowfall is causing Greenland to become warmer, according to a new study from Dartmouth College. The experts report that a weather pattern is pushing snowfall away from parts of Greenland’s ice sheet. As a result, older and darker snow is exposed that does not reflect sunlight as well as fresh snow.  

“As snow ages, even over hours to a few days, you get this reduction in reflectivity, and that’s why the fresh snow is so important,” explained Professor Erich Osterberg, the principal investigator of the study.

Without light-colored snow on its surface, the ice sheet loses its reflectivity, or albedo, and absorbs more heat from the sun. 

The researchers determined that the lack of snowfall has been driven by “atmospheric blocking.” This is characterized by persistent high-pressure systems that can hover over a region for weeks at a time.

Blocking events have increased over Greenland since the mid-1990s, pushing snowstorms to the north and holding warmer air over Western Greenland. The systems also reduce light-blocking cloud cover.

“It’s like a triple whammy effect,” said Professor Osterberg. “This all contributes to Greenland melting faster and faster.”

The researchers noted that the result of warmer air is not just less snowfall, but also an entirely different type of snow exposed on the surface.

As snowflakes melt, they become rounded and less reflective. This causes the snow surface to become darker. The experts found that a one percent change in reflectivity across Greenland’s ice sheet could cause an additional 25 gigatons of ice to be lost over three years.

“Fresh snow looks like what you would draw in a kindergarten class or cut from a piece of paper – it’s got all these really sharp points, and that’s because it’s extremely cold in the atmosphere when the snow falls,” said study first author Gabriel Lewis.

“Once it falls and sits on the surface of the ice sheet in the sun, it changes shape and the snow grains become larger over time.”

According to the study, the Greenland ice sheet has warmed by about 2.7 degrees Celsius since 1982. The continent is experiencing the greatest melt rates in at least 450 years, and these rates are likely the fastest in the last 7,000 years.

The study is published in the journal Geophysical Research Letters.

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By Chrissy Sexton, Earth.com Staff Writer