Friday, October 28, 2016

Antarctic Sea Ice Is Having A Rough Year, Too

A mountain near the western coast of Antarctica with a fractured
ice shelf to the left of it on the water. Ice shelves
are deteriorating in Antarctica, and that could mean
more global sea level rises. 
We've been watching the Arctic sea ice extent off and on all year in this here blog thingy because it's been struggling along at record lows, or near record lows most of the time.

That's not good news, of course, because the sea ice up there has been diminishing for decades, thanks in large part to global warming. That ice loss, in turn, might screw up northern hemispheric weather patterns.

For the record, the Arctic sea ice minimum for the season did not set a record low as some people expected, but after a quick start to the re-freeze season up there in September, lots of warm air has pushed into the Arctic in October, so the re-freeze has slowed down to a disconcerting crawl. 

There's a chance, perversely, that the low sea ice extent might be partly responsible for changes in the jet stream that have brought occasionally brutally cold and snowy winters to parts of North America and western Europe.

And now, let's take a look at the Antarctic, where things this year are not going so great, either. Ice extent there is among the lowest on record, which is a switch because the overall trend has been for increased ice extent around the Antarctic in recent decades.

Oh sure, some of the outer ice shelves have been eroding dangerously, but the overall sea ice has expanded somewhat, thanks to atmospheric circulation changes that caused upwelling of colder water around Antarctica that have promoted more easily freezable waters, notes Bob Henson at Weather Underground. 

Also, summertime melt water has increased from the Antarctic continent, reducing the salinity of the ocean water around there, making it easier to freeze.

This year, though, brought another shift in the weather patterns around Antarctica. It might be a one year deal, but it did break down the ice at the bottom of the Earth, that's for sure.

It remains to be seen if this year's low Antarctic ice extent is a one year shot, or the beginning of a trend.

A more worrisome development around Antarctica is the stability of the ice shelves.

Warmer ocean water seems to be chewing up the undersides of ice shelves along the coasts of Antarctica. These ice shelves act as dams that keep glaciers in place, or at least slow them down so they move at, um, a glacial pace down Antarctic slopes.

In the past, there's been basically an equilibrium. Some glacial ice makes it to the ocean and melts, but new ice is manufactured in the cold Antarctic interior, so all was good.

Since the ice shelves are melting more, that opens the door for the glaciers to move faster, going off into the sea and eventually melting.

The ice that comes down from the land and ends up in the ocean to melt is bad, because that contributes to global sea level rises. The new ice manufacturing process in Antarctica's interior can't keep up with the ice loss created by the newly speedy glaciers.

The problem can keep escalating because the more ice at the bottom of the ice shelf melts, the more is exposed to the warmer ocean water, and the melting just rolls on.

Still, the melting might have recently slowed a little bit, at least temporarily. The most intense ice shelf melting in Antarctica seems to have occurred between 2002 and 2009, notes NPR.

Even so, the fear is the melting will continue and the ice shelves in coastal Antarctic waters will collapse entirely, and the glaciers will flow toward the sea in a gallop. A gallop by glacial standards anyway.

That, in turn would accelerate sea level rises.

So yeah, people in toasty Miami and countless other coastal locations ought to care about what's going on in Antarctica. 

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