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Greenland's Ice Is Getting Darker And Melting Faster

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Although previous research shows that the global sea level rise has been slowed down by the hot, parched Earth, this does not mean the environmental phenomenon has been completely stopped.

An investigation into satellite data revealed that Greenland's icy surface has been turning darker for the past 20 years, further speeding up the melting of snow. As the country's snowy surface gets darker, its capacity to absorb heat from the sun increases as well.

Researchers said this trend is likely to continue in the coming years. Greenland's surface reflectivity or albedo - the fraction of solar energy reflected back into space - will decrease by about 10 percent by the end of the century.

The finding is important because melted snow from the country which pours into the ocean raises sea levels and could impact ocean ecology and circulation.

What Drives The Problem?

Marco Tedesco, the study's lead author and a research professor at Columbia University, said darker snowpack does not necessarily mean that it is dirtier. A snowpack that may seem "clean" to us can absorb more solar radiation than a dirty one, he said.

So what causes the problem?

Soot blown in from wildfires contributes to the problem in the region, but does not drive it. The real perpetrators are two feedback loops produced by the melting of snow. One of these feedback loops is not visible, but its effects are profound.

This is how feedback loops work: during a warm summer with clear skies, solar radiation pours in and the snowy surface begins to melt. The top layers of snow vanish and impurities such as dust and soot start to appear, darkening the surface. A warm summer can melt enough snow to allow accumulated dirt to concentrate at the surface.

As snow disappears and refreezes, the grains of snow get larger because meltwater acts like glue that sticks grains together during refreezing.

The large grains of snow produce a less reflective surface that allows the absorption of solar radiation. This impact is strong in the infrared range, but cannot be seen by humans. Thanks to satellite instruments, however, we can study them.

"Overall, what matters, it is the total amount of solar energy that the surface absorbs. This is the real driver of melting," said Tedesco.

It's a complex mechanism of interaction between the atmosphere and the snowpack, he said. It's a gigantic cycle: as temperatures rise, more melting occurs. As more snowpack melts, the surface reflectivity is reduced. As albedo decreases, more dirt appears and the surface absorbs heat.

How the cycle accumulates throughout the years is important, because it can speed up the amount of snowpack that Greenland loses.

"Even if we don't have a lot of melting because of atmospheric conditions one year, the surface is more sensitive to any kind of input the sun can give it, because of the previous cycle," said Tedesco.

Researchers had examined satellite data that focused on summertime changes in Greenland's albedo from 1981 to 2002. Starting 1996, the data showed that because of darkening, the ice had absorbed 2 percent more radiation per decade. At that time, summer near-surface temperatures in the country increased 0.74 degrees Celsius (33.3 degrees Fahrenheit) per decade, which allowed more snow to melt and drive the feedback loops.

Meanwhile, Tedesco said the feedback loops could be stopped with less melting and lots of snowfall, but it does not appear likely because of the rising levels of greenhouse gases in the atmosphere.

"As warming continues, the feedback from declining albedo will add up," added Tedesco. "It's a train running downhill, and the hill is getting steeper."

The team's findings are featured in the journal The Cryosphere.

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