Saturday, January 9, 2016

Last Week's Thaw At North Pole Is Least Of Our Arctic Worries

Arctic sea ice usually reaches its annual minimum in
September. Here's a graph from the NSIDC
showing the downward trend in Arctic sea ice
extent in Septembers since 1979 
Last week, all of us weather geeks got all wild and excited over a rare, very brief midwinter thaw right at the North Pole, the frigid, dark top of the world.

This was of course very odd, and perhaps a sign of global warming, perhaps not. I'll let the pundits and scientists and all that figure it out.

Whether or not the North Pole thaw was significant, there's still a lot going on up there, related to global warming, that we should probably be worried about.

Greenland is losing something like 287 tons of ice annual, mostly through melting and big chunks of ice falling off Greenland and floating away to melt, according to the Washington Post.

It could get worse, because something called "firn" on Greenland isn't doing as great as it once was.

Fern is porous snow that builds up on top of the ice most of the year. It slowly freezes into ice over time, which would add to Greenland's ice sheet if it weren't melting faster than it's freezing.

When it gets warmish in Greenland and melting starts, water trickles into the firn instead of running off into the ocean. Once the meltwater gets into the firn, it re-freezes, so the water doesn't run off the ice sheets of Greenland into the ocean.

Which is good, because all this excess water running off Greenland contributes to global sea level rises.

As the Washington Post reports, though, there's so much water trickling into the firn that it freezes everything up into hard dense ice. That means further melt water can't sink in and freeze into the firn, so it runs off into the oceans.

Even worse, the runoff can create channels in the ice surface of Greenland, creating slushy areas.

These slushy areas aren't as white as the ice and snow that already covers most of Greenland. You want things to be nice and white, because that reflects more sunlight off into space instead of heating the surface more.

If it's slushy and less white, more sunlight gets absorbed into Greenland's surface, and that accelerates the warming, which would make the Greenland melting go even faster.

Greenland in 2015. caught a break from the extreme melting of some previous years, most notably in 2012. The island in 2015 had its 11th most extensive summer melt in records dating back 37 years, says the National Snow and Ice Data Center.

Bad, but not as bad as it could have been.

Arctic sea ice overall isn't doing so hot, either.

Back in December, NOAA released its annual report on how the Arctic is doing, and the answer was not so great.

Sea ice up there reaches its maximum extent in late winter, and reaches a minimum in late summer, which of course makes perfect sense.

We learned from this report the the minimum in September was the fourth lowest on record. The maximum extent in February was even worse - the lowest on record.

Land masses up there were on average two degrees above normal for the 12-month period ending in September, 2015.

According to the Christian Science Monitor, climate change is reducing the amount of ice up there in the Arctic, and that loss of sea ice is having another effect: It's increasing the amount of precipitation that falls in the Arctic.

That makes sense. Open water and thawed ground evaporate more moisture into the air than expanses of ice do. More moisture in the air generally means increased odds of more precipitation.

That added precipitation could bring on a feedback loop: More rain falling on the Arctic would mean even more melting, and more climate change.

If the added precipitation falls mostly as snow, on the other hand, that would be a good thing. More widespread and deeper snow cover would help reflect the sun's energy out to space, which would have a bit of a slowing effect on global warming, notes the Christian Science Monitor.

The next step for scientists is to try to figure out if the added precipitation in the Arctic is going to be mostly rain, or mostly snow, or something more even-Steven.

Here's a fascinating video from NOAA depicting how sea ice in the Arctic has been diminishing over the past 25 years:

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