Ice Caps Grow and Shrink
October 24, 2012

Opposing Ice: Antarctic Grows While Arctic Ice Cap Shrinks

Brett Smith for — Your Universe Online

Over the past few years, researchers have consistently shown an overall decrease in the size of the Arctic ice cap–particularly during the summer months when the most melting occurs.

However, a new study from NASA scientists has shown that this melt off around the Arctic is accompanied by the record expansion of sea ice around Antarctica, when the Southern Hemisphere is experiencing its colder temperatures of the year.

According to the study, from 1978 to 2010 the total amount of sea ice around the southernmost continent grew by about 6,600 square miles every year. Previous studies from the same research group demonstrates that this rate of expansion has increased in recent years–up from 4,300 square miles per year between 1978 and 2006.

"There's been an overall increase in the sea ice cover in the Antarctic, which is the opposite of what is happening in the Arctic,” said lead author Claire Parkinson, a climate scientist with NASA's Goddard Space Flight Center in Greenbelt, Maryland. "However, this growth rate is not nearly as large as the decrease in the Arctic.”

Part of this bi-polar story can be told by the possible changes in atmospheric circulation being driven by the hole in the ozone layer above Antarctica. Recent research has suggested that a lack of ozone, which absorbs solar energy, leads to a cooler stratosphere over the South Pole. As this effect works in combination with increasingly warmer temperate zones, it could drive stronger winds across the Ross Ice Shelf, where the biggest growth in Antarctic sea ice has been observed.

"Winds off the Ross Ice Shelf are getting stronger and stronger, and that causes the sea ice to be pushed off the coast, which generates areas of open water, polynyas,” said Josefino Comiso, a senior scientist at Goddard. "The larger the coastal polynya, the more ice it produces, because in polynyas the water is in direct contact with the very cold winter atmosphere and rapidly freezes.” As the wind keeps blowing, the ice expands further to the north.”

While the sea ice during the austral winter appears to be expanding at a previously unseen rate, this does not disprove global warming, according to Parkinson.

"Climate does not change uniformly: The Earth is very large and the expectation definitely would be that there would be different changes in different regions of the world,” Parkinson said. "That's true even if overall the system is warming.”

Another recent NASA study supports Parkinson´s assertion, showing that Antarctic sea ice slightly thinned from 2003 to 2008. However, this thinning was taken into account during the latest study as increases in the extent of the ice more than compensated for the loss in thickness and led to an overall gain in volume.

The new study was the first to incorporate laser altimetry from the Ice, Cloud, and land Elevation Satellite (ICESat). The satellite could prove extremely useful in future Antarctic research as the logistics of analyzing sea ice on location has obvious complications. Currently, icebreakers are used to gather sea ice thickness information during the warmer months when the sailing conditions are most optimal.