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Pollution Causes Heat Island Effect on Ice Sheets

This article , originally posted in HuffPost Science, shows examples of heat island effect causing a positive feedback loop of melting snow and ice in Greenland. This is a suggested supplemental reading for the LEED Green Associate class and/or Continuing Education.

Greenland's Ice Sheet Is Filthy, And That's A Problem

Scientists have long known that Greenland's surface is neither green nor snowy white like you'll find on a world map. Rather, many of the country's massive ice fields have morphed into an ugly grey-black you'd find on the side of the road a few days after a blizzard.

Now, a new paper links this darkening of Greenland's ice to a familiar culprit, climate change, and warns that the worst is yet to come as the planet warms.

The study, published Thursday in the journal The Cyrosphere, suggests that a "feedback loop" of melting ice in turn causes the once-white landscape to collect impurities like soot, where it then soaks up more heat and melts further.

"We knew that these processes had been happening," Dr. Marco Tedesco, a professor at Columbia University's Lamont-Doherty Earth Observatory and lead author of the study, told The Christian Science Monitor. "What’s new is the acceleration of the darkening, which started in 1996."

Due to the ongoing plight of climate change, the Earth has seen year after year ofrecord-breaking warmth, which can cause several seasons' worth of snowfall to melt. Additionally, soot from global wildfires or atmospheric dust that has settled year after year then gets concentrated on the ground as surrounding snow layers disappear. This mixture of melted snow and atmospheric dust causes the black appearance.

"You have impurities stored in the snowpack, and as you start melting in the snow, part of the impurities will be flushed away, and the other part will be basically standing on the surface," Tedesco told The Washington Post. "Snow acts really like a filter. So the idea here is, the more you melt the snowpack, the more you will release these impurities on the surface of the snow, or the ice."

Other, less noticeable changes happen in another "feedback loop" when the melted snow and ice then refreezes into larger crystals that can absorb more solar radiation than before -- causing more melting.

"I call it melting cannibalism," Tedesco said in the Post. "You have melting feeding on itself."

For the study, the researchers analyzed satellite data to compare the reflectivity and darkening of Greenland's ice and snow from 1981 to 2012. White snow reflects more radiation from the sun, which keeps the ice cooler, while black snow absorbs radiation and leads to more ice melt.

The researchers also created a computer model to simulate the future of Greenland's surface temperature, grain size, exposed ice area and albedo.

They noticed that beginning around 1996, Greenland's ice began absorbing more solar radiation -- and they warn that the reflectivity of the ice could fall by as much as 10 percent by the end of the century, spurring further melt.

Tedesco and the paper's co-authors noted that the decrease in reflectivity could be stopped with a heavy bout of snowfall and less melting. But seeing as the world just had its hottest year on record in 2015, that option seems unlikely.

Scientists have long turned to Greenland to measure the impacts of climate change, since more than 650,000 square miles of the country are covered by a thick layer of snow and ice. Previous studies have shown that the ice sheets are shrinking at ever-increasing rates as glaciers retreat, and some scientists have warned the melt may soon become irreversible.

This drastic level of melt is the source of several climate-related doomsday scenarios that would force sea levels to rise dramatically, flooding many of the world's major cities. The new research sheds light on yet another process by which melting can occur.

"It’s worrying because if the ice sheet continues to get darker, it becomes more sensitive to atmospheric warming," Tedesco told The Guardian. "The impact of two weeks of sunshine with no clouds, for example, is far greater than it was 20 years ago. The ice is going to melt much more quickly, with more water flowing off on to the sea."

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