Why is Antarctic sea ice growing?

Oct 29, 2013 by Guy Williams
This winter there was more sea ice than ever in Antarctica. Credit: Flickr/august allen

Recently NASA reported that this year's maximum wintertime extent of Antarctic sea ice was the largest on record, even greater than the previous year's record.

This is understandably at odds with the public's perception of how should respond to a warming , given the dramatic headlines of severe decline in Arctic summertime extent. But the "paradox of Antarctic " has been on climate scientists' minds for some time.

Continental v. sea ice

First off, sea ice is different to the "continental ice" associated with polar ice caps, glaciers, ice shelves and icebergs. Continental ice is formed by the gradual deposition, build up and compaction of snow, resulting in ice that is hundreds to thousands of metres thick, storing and releasing freshwater that influences global sea-level over thousands of years.

Sea ice, though equally important to the climate system, is completely different. It is the thin layer (typically 1-2m) of ice that forms on the surface of the ocean when the latter is sufficiently cooled enough by the atmosphere.

From there sea ice can move with the winds and currents, continuing to grow both by freezing and through collisions (between the floes that make up the ice cover). When the atmosphere, and/or ocean is suitably warm again, such as in spring or if the sea ice has moved sufficiently towards the equator, then the sea ice melts again.

Antarctic v. Arctic

Secondly, we need to understand that the Arctic and Antarctic climate systems are very different, particularly in sea ice.

In the Arctic, sea ice forms in an ocean roughly centred on the North Pole that is surrounded by continents. A relatively large (though diminishing) proportion of the ice persists over multiple years before ultimately departing for warmer latitudes through exit points such as Fram Strait between Greenland and Svalbard.

In the south, on the other hand, sea ice forms outwards from the continental Antarctic Ice Sheet, where it is exposed to and strongly influenced by the winds and waters of the Southern Ocean. Here, there is a much stronger seasonal ebb and flow to sea ice coverage as over 80% of the sea ice area grows each autumn-winter and decays each spring-summer. This annual expansion-contraction from about 4 to 19 million square kms is one of the greatest seasonal changes on the Earth's surface.

Area v. volume

Finally we need to remember that "extent" or "areal coverage" is only one way with which we monitor and study sea ice.

Sea ice turns out to be a very complex and variable medium that is very difficult to observe over large-scales. It is also constantly moving and restructuring. Until we achieve the "holy grail" of monitoring total sea ice volume from space and how it changes over time (and there are great steps towards this with European Space Agency's environmental research satellite CryoSat-II), we are limited to interpreting its global behaviour through area.

What happened this winter?

This winter, the maximum total Antarctic was reported to be 19.47 million square kilometres, which is 3.6% above the winter average calculated from 1981 to 2010. This continues a trend that is weakly positive and remains in stark contrast to the decline in Arctic summer sea ice extent (2013 was 18% below the mean from 1981-2010).

To further complicate this picture, we find this net increase actually masks strong declines in particular regions around Antarctica, such as in the Bellingshausen Sea, which are on par or greater than those in the Arctic.

So while there is much greater attention given to the Arctic decline and the prediction of "ice-free summers" at the North Pole this century, Antarctic climate scientists still have their work cut out to understand the regional declines amidst the mild "net" expansion occurring in the southern hemisphere.

Here are some of the leading hypotheses currently being explored through a combination of satellite remote sensing, fieldwork in Antarctica and numerical model simulations – to help explain the increasing trend in overall Antarctic :

  • Increased westerly winds around the Southern Ocean, linked to changes in the large-scale atmospheric circulation related to ozone depletion, will see greater northward movement of sea ice, and hence extent, of Antarctic sea ice.
  • Increased precipitation, in the form of either rain or snow, will increase the density stratification between the upper and middle layers of the Southern Ocean. This might reduce the oceanic heat transfer from relatively warm waters at below the surface layer, and therefore enhancing conditions at the surface for sea ice.
  • Similarly, a freshening of the surface layers from this precipitation would also increase the local freezing point of sea ice formation.
  • Another potential source of cooling and freshening in the upper ocean around Antarctica is increased melting of Antarctic continental ice, through ocean/ice shelf interaction and iceberg decay.
  • The observed changes in sea ice extent could be influenced by a combination of all these factors and still fall within the bounds of natural variability.

The take home messages is that while the increase in total Antarctic sea ice area is relatively minor compared to the Arctic, it masks the fact that some regions are in strong decline. Given the complex interactions of winds and currents driving patterns of sea variability and change in the Southern Ocean climate system, this is not unexpected.

But it is still fascinating to study.

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User comments : 15

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runrig
3.8 / 5 (16) Oct 29, 2013
Quite succinctly explains what must be counter-intuitive, as the article says, to " the public's perception of how polar ice should respond to a warming climate".

The average person has an excuse but there are many contributors on here who don't and argue that somehow it's because GW is not happening. It is. There is no general cooling in the Antarctic seas or air above...
http://en.wikiped...2007.jpg

Yes climate responses to any redistribution of heat will be complex, especially when considering a medium where ice can form in a range of 0C to -2C, depending on salinity. and is mobile.
verkle
1.8 / 5 (31) Oct 29, 2013
So many caveats in this article. Just tell us the facts straight, without trying to come up with so many excuses. Ice is only made if temperatures drop. Period.

Interesting that the article compares maximum (winter) Antarctic sea ice extent to minimum (summer) Arctic ice extent. Why? Such fuddling of data is confusing at best.

deatopmg
1.5 / 5 (26) Oct 29, 2013
This increase in Antarctic ice is UNPRECEDENTED!
The increase in Arctic ice this year compared to last year is also UNPRECEDENTED.
It's interesting, to me, that Guy Williams' attempts to explain things away carefully avoids pointing out the real reasons for what is behind these UNPRECEDENTED increases:
It's the Sun, ...stupid!
It's also the present phases of the AMO and PDO.
It's also the insensitivity of Earths climate to CO2 concentration, e.g. no statistically significant warming for essentially 17 yrs, in spite of a 9% increase in CO2 concentration over that time.
It's All Natural.

Time to end this CAGW, state religion melodrama that is costing everyone ~$1000 million/DAY (~$1 billion/day). $1000 million PER DAY!!!

Wake up children, we are being fleeced by the "policy makers".

Sinister1811
3.5 / 5 (29) Oct 29, 2013
Could this have something to do with a change in wind and ocean currents? Very interesting.
ECOnservative
3 / 5 (23) Oct 29, 2013
Finally, we're beginning to understand how complex our planetary weather/climate patterns are. I only hope we're getting away from announcing vast conclusions based on somewhat less than vast data.
runrig
3.9 / 5 (15) Oct 29, 2013
So many caveats in this article. Just tell us the facts straight, without trying to come up with so many excuses. Ice is only made if temperatures drop. Period


This is, of course, true. However it misses the point.
The point is why is it growing when all thermometers are indicating no cooling.

Read my earlier post and the article.
runrig
4.1 / 5 (14) Oct 29, 2013
Could this have something to do with a change in wind and ocean currents? Very interesting.


Sinister: It can only be that and/or reduction in salinity

http://phys.org/n...ate.html
http://phys.org/n...ice.html
http://phys.org/n...293.html
BobSage
1.2 / 5 (18) Oct 29, 2013
Why do I suppose that if the Arctic ice were growing and the Antarctic ice shrinking that this line:

"we find this net increase actually masks strong declines in particular regions"

would be applied to the Arctic instead of the Antarctic.

And why is there no line about how the decrease in Arctic ice actually masks strong INCREASES in particular regions?

Because, it's a religion, folks. You are a true believer or you're out of the cult.
runrig
4 / 5 (12) Oct 29, 2013
Why do I suppose that if the Arctic ice were growing and the Antarctic ice shrinking that this line:

"we find this net increase actually masks strong declines in particular regions"

would be applied to the Arctic instead of the Antarctic.

And why is there no line about how the decrease in Arctic ice actually masks strong INCREASES in particular regions?

Because, it's a religion, folks. You are a true believer or you're out of the cult.


Err because the Arctic is enclosed and all of it freezes in winter. It has nowhere to go with often winds not allowing it out of the few outlets it has to escape. The Antarctic is not and the ice is free to be blown about ( preferential to prevailing winds).
ScooterG
1.5 / 5 (24) Oct 29, 2013
This article is nothing but concocted damage control.

The goal of every salesman is to turn negative into positive: ie more amperage draw on your power tool means more power, or (in this case) more ice is a sure-fire sign of agw.

Jay Carney would be proud of such bullsh*t!
djr
5 / 5 (11) Oct 30, 2013
deatopmg: "The increase in Arctic ice this year compared to last year is also UNPRECEDENTED."

Could you define UNPRECEDENTED for us? Take a look at the record.

http://www.arctic...ep13.png

Look back at about 1995. Doesn't that look about the same kind of recovery?
The Alchemist
1.7 / 5 (20) Oct 30, 2013
Good article, but, it misses the largest most obvious correlation; melting glacial ice releases cold non-saline water into-I should say "onto" the sea. This lighter water mixes poory and freezes easily.

That should about put the issue to bed for any denier who is not on a pay-roll,or simply insane.
The Alchemist
1.3 / 5 (13) Nov 02, 2013
Goodness @verkle-when ice feezes it releases energy into the environment. Lots of it-this is why the biggest snow storms hover around 0C/32F.

So scenario: Very cold water, lots of it, much lighter than sea water enters the sea during the day, when the temperature is say 33 F in the Sun.
At night the temperature drops by 5 degrees, and it freezes-there is now more ice. Has energy been added or removed from the system?
The Alchemist
1 / 5 (10) Nov 03, 2013
VendicarH, huh? Some people just can't take the hint.
Can't you vote for yourself by creating multiple usernames on another site-? Maybe FlatEarthers or some other up to your prowess?
nikola_novak_90
5 / 5 (1) Nov 05, 2013
I hate it when someone gives me percentages for comparison, when these percentages refer to two completely unrelated things. Let it be known exactly that the 3.6% increase from average in Antarctic sea ice during winter equals roughly 0.7 million square kilometers, whereas the 18% decrease from average in Arctic sea ice during summer equals roughly 1.6 million square kilometers. Because Arctic sea ice is smaller in surface - particularly during summer - precentages seem to blow the loss/gain ratio way out of proportion. The two quantities are, in fact, commensurate. The loss in Arctic is not more than 10 times greater than the gain in Antarctic, as percentages make it seem. It is only about 2.3 times greater.