Antarctic sea ice increase caused by winds
In support of their views, climate change skeptics have long pointed to the fact that Antarctic sea ice - unlike that in the Arctic - is actually growing.
Now, though, scientists from the British Antarctic Survey (BAS) and NASA's Jet Propulsion Laboratory (JPL) say they know why.
It's sea ice drift caused by changing weather patterns, they say, after examining over five million individual daily ice motion measurements captured over a period of 19 years by four US Defense Meteorological satellites.
"Until now these changes in ice drift were only speculated upon, using computer models of Antarctic winds," says Dr Paul Holland of BAS.
"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, says Holland, 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," he says.
"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."
The research also helps explain why changes in the amount of sea-ice cover are so different in the two polar regions. The Arctic has experienced dramatic ice losses in recent decades whi,le the overall extent of ice cover in the Antarctic has increased slightly.
This small Antarctic increase is actually the result of much larger regional increases and decreases, says the team, which are now shown to be caused by wind-driven changes. In places, it now appears, increased northward winds have caused the sea-ice cover to expand outwards from Antarctica. But because the Arctic Ocean is surrounded by land, changed winds can't cause Arctic ice tomake it expand in the same way.
"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," says Dr Ron Kwok of JPL.