Global climate change

Why is Sea Ice Increasing in the Antarctic?

9/20/2013, 7:57:51 AM

The annual maximum sea ice extent in the Antarctic will likely reach another record high for the second year in a row.

The latest Antarctic Sea Ice extent compared to 2012 and the 1981-2010 average. Courtesy of the NSIDC.


The latest Antarctic sea ice extent compared to normal (orange line). Image courtesy the NSIDC.


How are these record maximums possible when there is overwhelming evidence which shows that the Southern Ocean is warming?

To find out, a research team led by Jinlun Zhang, an oceanographer at the University of Washington's Applied Physics Laboratory performed a new computer modeling study that showed stronger polar winds produced an increase in Antarctic Sea ice, even in a warming climate.

The results of the study showed that stronger westerly winds around the South Pole can explain 80 percent of the small increase in Antarctic Sea ice volume over the past 30 years. A previous study by Zhang showed that changes in water density could explain the remaining 20 percent of the increase.

Why have the winds been getting stronger? Researchers are not quite sure, but it could be due to ozone depletion, global warming or natural cycles.

Key excerpts from the University of Washington article.....

The polar vortex that swirls around the South Pole is not just stronger than it was when satellite records began in the 1970s, it has more convergence, meaning it shoves the sea ice together to cause ridging. Stronger winds also drive ice faster, which leads to still more deformation and ridging. This creates thicker, longer-lasting ice, while exposing surrounding water and thin ice to the blistering cold winds that cause more ice growth.

Differences between the two poles could explain why they are not behaving in the same way. Surface air warming in the Arctic appears to be greater and more uniform, Zhang said. Another difference is that northern water is in a fairly protected basin, while the Antarctic sea ice floats in open oceans where it expands freely in winter and melts almost completely in summer.

The sea ice uptick in Antarctica is small compared with the amount being lost in the Arctic, meaning there is an overall decrease in sea ice worldwide.

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Global climate change