ARCTIC ICE DECREASING AND ANTARCTIC ICE INCREASING

         Much attention is paid to melting sea ice in the Arctic. But less clear is the situation on the other side of the planet. Despite warmer air and oceans, there is more sea ice in Antarctica now than in the 1970s- a fact often pounded on by global warming sceptics. The latest members suggest the Antarctica sea ice may be heading toward a record this year.

           A researcher of the University of Washington says the reason lie in the winds. A new modelling study to be published in the Journal of Climate shows that stronger polar winds lead to an increase in Antarctic sea ice, even in a warming climate.

           “The overwhelming evidence is that the Southern Ocean is warming”, said the author Jinlun Zhang, an oceanographer at the UW Applied Physics Laboratory. “Why would sea ice be increasing? Although the rate of increase is small, it is a puzzle to scientists.”

            His new study shows that stronger westerly winds swirling around the South Pole can explain 80% of the increase in Antarctica sea ice volume in the past three decades.

           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.

         In a computer simulation that includes detailed interactions between wind and the sea, thicker ice- more than 6 feet deep– increased by about 1% every year from 1979 to 2010. While the amount of thin ice stayed fairly constant. The end result is a thicker, slightly larger ice pack that lasts longer into summer.

         When the model held the polar winds at a constant level, the sea ice increased only 20% as much. A previous study by Zhang showed that changes in water density could explain the remaining increase.

       “People have been talking about the possible link between winds and Antarctica sea ice expansion before, but I think this is the first study that confirms this link though a model experiment.” Said by Alex Schweiger, a polar scientist at the UW Applied Physics Lab. “This is another process by which dynamic changes in the atmosphere can make changes in sea ice that are not necessarily expected.”

     The research was funded by the National Science Foundation.

   Though, it is still a mystery why the southern winds have been getting stronger, some scientist have theorized that it could be related to global warming or to the Ozone depletion in the southern hemisphere or just to natural cycles of variability. Difference between the two poles could explain the opposite behave. Surface air warming in the Arctic is more uniform. Another difference in the Arctic is that, the Northern hemisphere is protected basin, while the Antarctic sea ice floats in open oceans where the ice can expand freely. Many of the models are unable to explain why the Antarctic ice increases.

“If the warming continues, at some point the trend will reverse