Climate studies probe growth of Antarctic sea ice

‘The planet as a whole is doing what was expected in terms of warming. Sea ice as a whole is decreasing as expected …’

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Sea ice is expanding around Antarctica, and scientists say wind, snow and melting land ice are key factors in the growth bberwyn photo.
The map at right shows Antarctic ice concentration on September 22, 2014, the date of the record high. Areas where the surface was less than 15% ice covered are deep blue; areas that were up to 100% ice covered are shades of light blue to white. The orange line shows the 1981-2010 median extent for September 22. (Median means in the middle: half of the years in the record had smaller ice extents than this, and half had larger extents.) The graph below the map shows daily Antarctic sea ice extent over the course of the year. The black line traces the 1981-2010 average, and the gray shading shows the range of variability (2 standard deviations from the mean). The previous record high extent (2013) is a dashed green line; the 2014 year to date is a light green line. NSIDC reported that the 2014 extent rose nearly 4 standard deviations above the 1981-2010 mean.
The map above shows Antarctic ice concentration on September 22, 2014, the date of the record high. Areas where the surface was less than 15% ice covered are deep blue; areas that were up to 100% ice covered are shades of light blue to white. The orange line shows the 1981-2010 median extent for September 22. (Median means in the middle: half of the years in the record had smaller ice extents than this, and half had larger extents.)
The graph below the map shows daily Antarctic sea ice extent over the course of the year. The black line traces the 1981-2010 average, and the gray shading shows the range of variability (2 standard deviations from the mean). The previous record high extent (2013) is a dashed green line; the 2014 year to date is a light green line. NSIDC reported that the 2014 extent rose nearly 4 standard deviations above the 1981-2010 mean. Courtesy NOAA.

By Summit Voice

FRISCO — Along with shifting wind patterns in the southern hemisphere, melting land ice may be contributing to recent record extents of floating sea ice around Antarctica. The melting ice and snow adds fresh water — which freezes morel easily — to the salty Southern Ocean, scientists said in a release this week, explaining the multi-year trend of expanding Antarctic sea ice.

But the increase doesn’t balance the loss of sea ice at the other end of the Earth. Arctic sea ice has declined by an average of 20,800 square miles per year; the Antarctic has gained ice at a rate of about a third of that, by an average of 7,300 square miles per year.

This week, the National Snow and Ice Data Center (NSIDC) reported that Antarctic sea ice extent set a new record high for daily extent: 20.11 million square kilometers (7.76 million square miles), the highest since satellite observations started in the late 1970s.

In July, a European study called into question the recent measurements, citing inconsistencies in computer models.

Other studies suggest the growth is only temporary, and that Antarctic sea ice will ultimately decline dramatically in the decades ahead.

The ice trackers matched this year’s late season ice surge with strong southerly winds blew over the Weddell Sea. Without any nearby land masses to constrain growth, those winds tend to push the ice northward.

The new Antarctic sea ice record reflects the diversity and complexity of Earth’s environments, said NASA researchers.

“The planet as a whole is doing what was expected in terms of warming. Sea ice as a whole is decreasing as expected, but just like with global warming, not every location with sea ice will have a downward trend in ice extent,” Parkinson said.

Top scientists said that, while it may appear counterintuitive, expanding winter Antarctic sea ice may be a manifestation of recent warming.

“Both the Arctic and the Antarctic are responding to climate change, and both have areas that are warming rapidly,” explains NSIDC lead scientist Ted Scambos. “But Antarctic sea ice is responding to wind shifts and ocean changes in an unexpected way, and we’re still trying to fully understand it.”

A warming climate changes weather patterns, said Walt Meier, a research scientist at Goddard. Sometimes those weather patterns will bring cooler air to some areas. And in the Antarctic, where sea ice circles the continent and covers such a large area, it doesn’t take that much additional ice extent to set a new record.

“Part of it is just the geography and geometry. With no northern barrier around the whole perimeter of the ice, the ice can easily expand if conditions are favorable,” he said.

Researchers are investigating a number of other possible explanations as well. One clue, Parkinson said, could be found around the Antarctic Peninsula – a finger of land stretching up toward South America. There, the temperatures are warming, and in the Bellingshausen Sea just to the west of the peninsula the sea ice is shrinking. Beyond the Bellingshausen Sea and past the Amundsen Sea, lies the Ross Sea – where much of the sea ice growth is occurring.

Snowfall could be a factor as well, Meier said. Snow landing on thin ice can actually push the thin ice below the water, which then allows cold ocean water to seep up through the ice and flood the snow – leading to a slushy mixture that freezes in the cold atmosphere and adds to the thickness of the ice. This new, thicker ice would be more resilient to melting.

“There hasn’t been one explanation yet that I’d say has become a consensus, where people say, ‘We’ve nailed it, this is why it’s happening,’” Parkinson said. “Our models are improving, but they’re far from perfect. One by one, scientists are figuring out that particular variables are more important than we thought years ago, and one by one those variables are getting incorporated into the models.”

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