Thursday, 8 December 2016

Low sea ice in the Arctic ....and Antarctic

From pole to pole, twin sea ice records have scientists stunned
Chris Mooney


6 December, 2016

We already knew there was something pretty odd about last month, November, in the Arctic. And in the Antarctic. At both poles, much of the floating sea ice that usually covers the chilling ocean waters was just … missing.

Now, the National Snow and Ice Data Center has officially crunched the numbers, and it is affirmed: Both the Arctic and the Antarctic were pushing new boundaries for low sea ice. We’ll let the scientists say it in their own words, because sometimes the calm language of statistics and measured analysis is enough:

Average Arctic sea ice extent for November set a record low, reflecting unusually high air temperatures, winds from the south, and a warm ocean. Since October, Arctic ice extent has been more than two standard deviations lower than the long-term average. Antarctic sea ice extent quickly declined in November, also setting a record low for the month and tracking more than two standard deviations below average during the entire month. For the globe as a whole, sea ice cover was exceptionally low.

As you can see in the figure above, Antarctic sea ice in November — the beginning of austral summer — had actually been ticking upward slightly in recent years. But in 2016 it just totally falls off a cliff.

The chart for the Arctic in November isn’t quite so dramatic, in large part because this region is already seeing a major sea ice downtrend tied to global warming — but it’s still pretty dramatic. Here it is:



Moreover, it isn’t just about the extent of sea ice — it’s the thickness of it. Its volume. That also appears to be at an extreme low, at least in the Arctic:

November sea ice volume was the lowest in the satellite record (PIOMAS) for the month... ~400 km^3 less than 2012

So what is going on here?

In the Arctic, the explanation is simpler — temperatures have just been extremely warm, so the ice hasn’t been able to refreeze, heading into winter, in the way that it normally would. In fact, there was even a super anomalous period during the month when it actually shrank, “an almost unprecedented occurrence for November over the period of satellite observations,” says the center.

Air temperatures at the 925 hPa level (about 2,500 feet above sea level) were above the 1981 to 2010 average over the entire Arctic Ocean and, locally up to 10 degrees Celsius (18 degrees Fahrenheit) above average near the North Pole,” notes the group. And that’s for the entire month of November.

In contrast, Antarctica’s behavior is more mysterious. Warmer than average air temperatures were again part of the story — though not as dramatically as in the Arctic. But what seems to also have been dramatic is shifting wind patterns around Antarctica, which created areas with little ice.

The Antarctic is interesting because it had been high in recent years. Maybe this marks a turn toward a declining trend, but it’s far too soon to say for sure,” said Walt Meier, a sea ice expert with NASA.

This leads to a total picture in which global sea ice — the Arctic and Antarctic summed together — is just extremely low:

Now, granted, some scientists do not particularly like grouping Antarctic and Arctic sea ice together to create a figure like this one. After all, the Arctic record came at a time when the ice was refreezing, while the Antarctic one came at a time when it is melting — each according to its seasonal cycle, but in opposite hemispheres.



It really is stunning,” said Meier of the twin low records. “But I’d hesitate to draw any major conclusions. ‘Global’ sea ice is not really indicative because the environments are so different. And of course they’re in opposite seasons.”

They are. And yet here we stand with twin records — synchronous, bizarre, and hard not to be struck by.



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