See larger image here.
The melt season in Greenland starts every spring or early summer. The melting white snow and ice that accumulated on the ice sheet surface over the winter transforms to a blue meltwater. The melt season also exposes the old snow and ice, darkening the ice sheet surface. This old ice can be as much as 30 percent less reflective than younger snow and ice. This dark ice absorbs more energy from the sun, which leads to even more melting and a further darkening of the Greenland ice sheet surface. This is called the albedo effect, a feedback loop, and it threatens the world’s coast lines with sea level rise.
Acquired June 10, 2014: Marco Tedesco, a professor at Columbia University’s Lamont Doherty Earth Observatory stated that 2014 was not an exceptional melting year. The season was generally colder and wetter, and it’s possible that there’s even some recent snowfall visible in the image.See larger image here.
NASA’s Earth Observatory reports:
“This year we had some really early season melt events that kick-started things,” said Allen Pope, a scientist at the National Snow & Ice Data Center (NSIDC). According to an NSIDC blog post, the ice sheet saw three extreme spikes in melt by June 19. As a result, the pace of melting so far is ahead of the past three seasons, but behind the record melt year of 2012.
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Surface melt can directly contribute to sea level rise via runoff. It can also force its way through crevasses to the base of a glacier, temporarily speeding up ice flow and indirectly contributing to sea level rise. Also, ponding of meltwater can “darken” the ice sheet’s surface and lead to further melting.
“All these processes tend to accelerate further melting through so-called positive feedback mechanisms,” Tedesco said. “The more melting you have, the more melting will increase in a way that melting feeds on itself. I call this melting cannibalism.”
Not every melt season follows the same progression. Pope notes that almost no lake water was present in mid-June in 2014 and 2015, then volumes of meltwater peaked each year by mid-July.
Melt ponds and rivers that form on the ice surface are not only indicators of melting, but they also can provide a glimpse of how fast glaciers will calve ice into the ocean. These melt ponds drain via a Moulin ( a vertical shaft through miles deep ice to the bedrock) or a crevasse. Once the water gushes to the bottom it flows between the ice and the bedrock lubricating the base of the glacier, allowing it to flow more smoothly over the land surface and to shed ice more quickly at the coasts. It is not simple melting from climate change that puts the Greenland ice sheet in danger, it is that climate change causes the dynamics of the ice sheet to change allowing it to flow rapidly to the sea.
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