Paradoxically, the Antarctic sea ice is expanding and thickening despite warming waters worldwide. The strange phenomenon has puzzled scientists and fueled countless debates on global warming’s validity for years.
But a group of U.S. and Australian researchers believe that they may finally have an explanation. They claim that natural variability may play a huge role in the sea ice expansion.
According to a study recently published in Nature Geoscience, natural variation in sea temperatures and changes in the atmospheric pressure in the Pacific Basin may be behind the sea ice increase.
Scientists noticed that sea ice in the Antarctic was expanding in 1979, when they were first able to analyze satellite data. By contrast, the Arctic has been thawing rapidly ever since.
Researchers explained that in the Antarctic, the Interdecadal Pacific Oscillation (IPO), a natural variation in the atmospheric pressure across the tropical Pacific Ocean, has accelerated the rise in sea ice levels in Antarctica starting in the late 1990s.
The IPO has a two to three decade cycle and scientists believe that in 2014 it ended its negative phase, which is marked by dips in ocean temperatures.
According to study’s background information, sea ice in the Antarctic is a seasonal phenomenon which occurs when water temperatures get below -2 degrees C. The IPO has cooled the sea temperature in the Pacific Basin in recent years and offset global warming effects in the region.
A significant increase in sea ice was observed in 2000, especially in the western parts of the Antarctic in the Ross Sea where sea ice expanded all seasons. James Renwick of the Victoria University who hasn’t contributed to the study explained that surface winds also played a part in the cooling trend.
Cool winds can pull cold off continent towards water and help it freeze, as they can also move ice around and push the heat from the ice, Renwick explained. The researcher added that the IPO also accelerated the effect of surface winds in the region.
Furthermore, between the 1970s and 1990s there have been may El Nino events, but in recent years scientists observed mostly La Nina events. While El Nino is coupled with widespread sea warming, La Nina usually brings sea surface temperatures that are lower than usual by up to 5 degrees C.
All the said natural phenomena contributed to the peak of the sea ice expansion in the Antarctic in 2014, when satellites recorded an increase of 20 million square km, researchers suggest.
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