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Antarctic Sea Ice Grows as Result of Warming

By Tim Radford, Climate News Network

LONDON — The Arctic may be shrinking as the world warms but Antarctic sea ice is expanding. Blame global warming for that, too, say Dutch scientists.

The paradox is that increasing temperatures have set in motion a chain of events in the southern seas that have the opposite effect. Engineers call this negative feedback. So do Richard Bintanja and colleagues of the Royal Netherlands Meteorological Institute.

An Antarctic iceberg in the Amundsen Sea.
Credit: NASA.

They report in Nature Geoscience that as the Antarctic ice shelves melt, the resulting cool fresh water has actually served to insulate the offshore sea ice from the warming ocean beneath the floating floes. So, as a consequence, in 2010 southern ocean sea ice reached a record extent.

The Arctic Ocean is mostly just that: ocean, which is getting warmer, and the northernmost parts of the globe have been warming at twice the global average rate.

So the north polar sea ice has been steadily thinning in depth and shrinking in area for more than 30 years. Ice reflects sunlight and keeps itself cold. Dark seas absorb sunlight and continue to get warmer.

As the Arctic ice shrinks, the feedback becomes positive. So the expectation is that sometime this century, in late summer, the Arctic ocean will for a few weeks be ice-free.

Plausible — and Conclusive?

But Antarctica is an enormous, high continental landmass covered almost entirely by a huge depth of ice and snow, and it keeps itself cold very effectively. The oceans as a whole are warming — but in Antarctica, this warming has a counter-intuitive effect: thanks to the melt water, the total area of reflective sea ice is stable, or getting larger.

So although warm water is reaching the continental shelves, and creating some melting, the overall effect is to deliver a cold freshwater layer to the top hundred metres or so of the surrounding ocean. Fresh water freezes more quickly, so sea ice builds up quickly in the autumn and early winter.

“Our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt”, the Dutch scientists report.  “We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.”

That should be good news: there is enough ice on the southern continent to completely inundate most of the world’s great estuarine and sea level cities.  But the conclusions are tentative and not everybody is likely to agree.

Is this an effect that will last? The interaction of ocean and atmosphere is a complicated one, with a number of factors at work that influence the growth of sea ice. In the UK, Martin Siegert of the University of Bristol suspects that the process just described may not be significant in the long run.

Paul Holland of the British Antarctic Survey calls the freshwater concept “plausible” but thinks there are also plausible alternative explanations for the increase in sea ice around Antarctica, among them changes in the wind patterns that might deliver blasts of colder air to the surrounding seas.

Galloping Change

And Andrew Russell of Brunel University agrees: he sees both wind pattern changes and ice shelf melting resulting in increased sea ice “which perhaps isn’t what you’d expect but is consistent with our best description of climate change.”

Meanwhile, scientists at the American Museum of Natural History have more bad news for polar bears and other creatures adapted to the frozen Arctic. It will get warmer, and greener.

Rising temperatures in the next few decades will lead to a “massive” increase in vegetation in the lands bordering the Arctic, with as much as 50 percent more tree cover.

Three weeks ago, an international team reported in Nature Climate Change that vegetation conditions had advanced hundreds of miles north in the last few decades.

Now a consortium of researchers from the New York museum, Woods Hole research center, Cornell University, and the University of York in the U.K. report in the same journal that the growth will continue.

They used climate models to simulate future conditions and they believe that positive feedback will guarantee the advance of mosses, dwarf shrubs, sedges, grasses and even trees towards the pole. As the ice and snow give way to green foliage, the rate of warming will step up.

“These impacts would extend far beyond the Arctic region,” said Richard Pearson of the American Natural History Museum. “For example some species of birds seasonally migrate from lower latitudes and rely on finding particular polar habitats, such as open space for ground nesting.”

Tim Radford is a report for the Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.


By AndrewXnn (New York)
on April 7th, 2013

Thanks for the nice article.

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By dan_in_illinois
on April 8th, 2013

Let me see if I understand this…

Warming in the Antarctica causes the Antarctic ice to increase but warming in the Arctic causes the ice to increase?  According to the article, “Engineers call this negative feedback”.  I’m quite familiar with negative feedback, but I wonder - if negative feedback causes a dramatic increase in ice content at one polar region, why doesn’t negative feedback cause a similar phenomenon in the other polar region?

This global warming sure is complicated.  It’s a good thing there are all of these “experts” who can spin things - I mean, explain things - to the rest of us.

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By A_Person (Three Rivers/MI/49093)
on December 29th, 2013

Well, clearly, you don’t understand, as you have just admitted. So let’s just ignore all of the warnings until the earth is no longer habitable, shall we? “I don’t understand, so they must be wrong”, right?

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By Dave
on April 8th, 2013

Dan: The authors of this paper suggest a possible mechanism by which the accelerated ice sheet melting on Antarctica may be acting to cause a greater area of sea ice to form around that continent. Despite being much colder than the Arctic, partly due to higher average elevation, the current trend is that Antarctica is losing land ice mass. Perhaps the greater extent of seasonal sea ice may act to help slow this down by the greater seasonal albedo enhancement…

NASA data: Loss in Antarctic ice mass between 2003 and 2011.  (GRACE measurements.) The y axis is Gt per year.

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By Rollin (New Jersey)
on April 8th, 2013

This is just a letter, not a peer reviewed article. The claim that some sea ice increase is counteracting southern hemisphere warming seems a bit grandiose. I think we need some corroborating evidence and studies before jumping to large conclusions.
An interesting observation, sea ice is at the mercy of ocean temperature. Sea ice can quickly and dramatically disappear.  I wonder if the cold water will maintain or if it will disturb ocean thermal currents.

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By Susan_From_APlace (Three Rivers/MI/49093)
on December 29th, 2013

So how much evidence, would you say, would be enough? Should we quantify just how many animal and plant species we should let die out, before we can say that is enough evidence? Because at some point, it will be too late. The effects will no longer be able to be reversed. But I agree, I think we should keep gathering evidence. At least for another 100 years or so. Because I just don’t believe that if the entire planet is not blazing that global warming is actually real.

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By Dave (Basking Ridge, NJ 07920)
on April 9th, 2013

Rollin: That thought – i.e. effects on THC - occurred to me. Unlike the North Atlantic the THC doesn’t overturn in the southern ocean. I’m no expert in this, but I imagine that any mechanism for it to significantly disturb local THC components such as the circumpolar current, would be different from that for the AMOC due to Arctic melt water.  On the other hand, it seems likely that a greater sea ice extent will directly impact biological productivity in the region. Perhaps this may also incrementally affect net CO2 uptake in the southern ocean as well.

BTW: Apparently “letters” are peer reviewed.

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By Dave (Basking Ridge, NJ 07920)
on April 10th, 2013

For anyone interested I found this dated reference concerning the interrelationships between Antarctic sea ice and THC, etc.
“Southern Ocean: THC, Ocean-Ice Interactions and Global Climate”
Lecturer: Doug Martinson, LDEO, Columbia University.
Also, apparently overturning does occur in the southern ocean.

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By Dan Whelan (LONGBOAT KEY FL 34228)
on June 20th, 2013

Jeez, who makes this stuff up.  Summer temperatures in Antarctica rarely get above 0 degrees C, the melting point of water.  High temperatures in the summer months average between minus 5 and plus 5 degrees C.  Very, very occasionally temps might rise slightly higher.

It simply never gets warm enough or stays warm enough to cause any significant melting—certainly not enough to explain sea ice expansion of more than 1 million square miles above the 1979-2013 average area.

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By Ernest H. (Anchorage, AK)
on September 25th, 2013

It’s really a shame that ‘scientists’ can’t be disbarred for malfeasance, the lawyers are.  Good lord.

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