‘The overwhelming evidence is that the Southern Ocean is warming,’ said the study’s author, Jinlun Zhang of the University of Washington. ‘Why would sea ice be increasing? Although the rate of increase is small, it’s a puzzle to scientists.’
The polar vortex – the westerly winds that swirl around the South Pole – is stronger than it was when satellite records began in the 1970s. Using computer simulations that modelled the interaction between wind and sea, Zhang showed that 80 per cent of the growth in Antarctic sea ice over the past 30 years can be attributed to this increase in wind strength. His results indicated that in that period, sea ice more than two metres thick grew by one per cent per year.
The polar vortex forces sheets of sea ice together, leading to a build-up of ice ridges that make the ice thicker and hence longer lasting. The cold winds also cause more ice growth in the exposed water.
‘You’ve got more thick ice, more ridged ice, and at the same time you will get more ice extent because the ice just survives longer,’ said Zhang.
This story was published in the November 2013 edition of Geographical Magazine