Why Antarctic Sea Ice Cover is Increasing Under Climate Change
Last month I wrote an article entitled ‘Antarctica and Arctic Polar Opposites‘ that looked at a study which showed that “the total extent of sea ice surrounding Antarctica in the Southern Ocean grew by roughly 6,600 square miles every year, with recent research adding that that growth rate has accelerated recently, up from an average rate of almost 4,300 square miles per year from 1978 to 2006.”
This month, a new study published in the journal Nature Geoscience by scientists from NERC’s British Antarctic Survey (BAS) and NASA’s Jet Propulsion Laboratory (JPL), Pasadena California shows that the contrary changes to Antarctic sea ice drift that have occurred over the past two decades is due to changing winds.
The scientists explain that the Antarctic sea ice cover has increased under the effects of climate change, rather than decreasing such as has been seen on the opposite side of the planet in the Arctic. Working from maps created by JPL using over 5 million individual daily ice motion measurements captured over a period of 19 years by four US Defense Meteorological satellites, the scientists were able to see for the first time long-term changes in sea ice drift around the southern continent.
“Until now these changes in ice drift were only speculated upon, using computer models of Antarctic winds, said lead author, Dr Paul Holland of BAS. “This study of direct satellite observations shows the complexity of climate change. The total Antarctic sea-ice cover is increasing slowly, but individual regions are actually experiencing much larger gains and losses that are almost offsetting each other overall.”
“We now know that these regional changes are caused by changes in the winds, which in turn affect the ice cover through changes in both ice drift and air temperature. The changes in ice drift also suggest large changes in the ocean surrounding Antarctica, which is very sensitive to the cold and salty water produced by sea-ice growth.”
“Sea ice is constantly on the move; around Antarctica the ice is blown away from the continent by strong northward winds. Since 1992 this ice drift has changed. In some areas the export of ice away from Antarctica has doubled, while in others it has decreased significantly.”
Antarctica has not seen a simple overall growth of sea ice. In fact, the evident growth is actually the result of much larger regional increases and decreases, resulting from changes in the winds. The impact of wind changes has seen increased ice-cover to expand out from Antarctica, while the Arctic — which is completely landlocked — is unaffected by such changes.
“The Antarctic sea ice cover interacts with the global climate system very differently than that of the Arctic, and these results highlight the sensitivity of the Antarctic ice coverage to changes in the strength of the winds around the continent,” said Dr Ron Kwok of JPL.
One very important distinction to make, however, is that these changes in wind are affecting the sea ice cover that expands outward from the continent during it’s annual winter freeze. These changes have virtually no impact upon the the Antarctic Ice Sheet which is losing volume each year.