Antarctic Sea Ice Reaches New Record Maximum

On Sept. 19, 2014, the five-day average of Antarctic sea ice extent exceeded 20 million square kilometers for the first time since 1979, according to the National Snow and Ice Data Center. The red line shows the average maximum extent from 1979-2014.

Credits: NASA's Scientific Visualization Studio/Cindy Starr

Sea ice surrounding Antarctica reached a new record high extent this year, covering more of the southern oceans than it has since scientists began a long-term satellite record to map sea ice extent in the late 1970s. The upward trend in the Antarctic, however, is only about a third of the magnitude of the rapid loss of sea ice in the Arctic Ocean. The new Antarctic sea ice record reflects the diversity and complexity of Earth’s environments, said NASA researchers. Claire Parkinson, a senior scientist at NASA’s Goddard Space Flight Center, has referred to changes in sea ice coverage as a microcosm of global climate change. Just as the temperatures in some regions of the planet are colder than average, even in our warming world, Antarctic sea ice has been increasing and bucking the overall trend of ice loss.

“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.

Since the late 1970s, the Arctic has lost an average of 20,800 square miles (53,900 square kilometers) of ice a year; the Antarctic has gained an average of 7,300 square miles (18,900 sq km). On Sept. 19 this year, for the first time ever since 1979, Antarctic sea ice extent exceeded 7.72 million square miles (20 million square kilometers), according to the National Snow and Ice Data Center. The ice extent stayed above this benchmark extent for several days. The average maximum extent between 1981 and 2010 was 7.23 million square miles (18.72 million square kilometers).

The single-day maximum extent this year was reached on Sept. 20, according to NSIDC data, when the sea ice covered  7.78 million square miles (20.14 million square kilometers). This year's five-day average maximum was reached on Sept. 22, when sea ice covered 7.76 million square miles (20.11 million square kilometers), according to NSIDC.

This year, Antarctic sea ice reached a record maximum extent while the Arctic reached a minimum extent in the ten lowest since satellite records began. Why are these trends going in opposite directions?

Credits: NASA Goddard Space Flight Center/Joy Ng

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.

A Q&A with NASA Goddard Space Flight Center’s Joey Comiso – a sea ice scientist and lead author of the cryosphere observations chapter in the Fifth Assessment of the Intergovernmental Panel on Climate Change – about what’s going on with the sea ice in Antarctica.

Credits: NASA/M. Studinger

That suggests that a low-pressure system centered in the Amundsen Sea could be intensifying or becoming more frequent in the area, she said – changing the wind patterns and circulating warm air over the peninsula, while sweeping cold air from the Antarctic continent over the Ross Sea. This, and other wind and lower atmospheric pattern changes, could be influenced by the ozone hole higher up in the atmosphere – a possibility that has received scientific attention in the past several years, Parkinson said.

“The winds really play a big role,” Meier said. They whip around the continent, constantly pushing the thin ice. And if they change direction or get stronger in a more Northward direction, he said, they push the ice further and grow the extent.  When researchers measure ice extent, they look for areas of ocean where at least 15 percent is covered by sea ice.

While scientists have observed some stronger-than-normal pressure systems – which increase winds – over the last month or so, that element alone is probably not the reason for this year’s record extent, Meier said. To better understand this year and the overall increase in Antarctic sea ice, scientists are looking at other possibilities as well.

Melting ice on the edges of the Antarctic continent could be leading to more fresh, just-above-freezing water, which makes refreezing into sea ice easier, Parkinson said. Or changes in water circulation patterns, bringing colder waters up to the surface around the landmass, could help grow more ice.

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.

Five new NASA Earth science missions are launching in 2014 to expand our understanding of Earth’s changing climate and environment.

NASA's "Earth Right Now" website

“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.”

For Antarctica, key variables include the atmospheric and oceanic conditions, as well as the effects of an icy land surface, changing atmospheric chemistry, the ozone hole, months of darkness and more.

“Its really not surprising to people in the climate field that not every location on the face of Earth is acting as expected – it would be amazing if everything did,” Parkinson said. “The Antarctic sea ice is one of those areas where things have not gone entirely as expected. So it’s natural for scientists to ask, ‘OK, this isn’t what we expected, now how can we explain it?’”

Reproduced from Nasa

http://www.nasa.gov/content/goddard/antarctic-sea-ice-reaches-new-record-maximum

Ice in Antarctic is increasing 

Reproduced from reportingclimatescience.com

A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.

The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice.

According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed   to 82 billion tons of ice per year between 2003 and 2008.

“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas.”  Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”

Scientists calculate how much the ice sheet is growing or shrinking from the changes in surface height that are measured by the satellite altimeters. In locations where the amount of new snowfall accumulating on an ice sheet is not equal to the ice flow downward and outward to the ocean, the surface height changes and the ice-sheet mass grows or shrinks.

But it might only take a few decades for Antarctica’s growth to reverse, according to Zwally. “If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years -- I don’t think there will be enough snowfall increase to offset these losses.”

The study analyzed changes in the surface height of the Antarctic ice sheet measured by radar altimeters on two European Space Agency European Remote Sensing (ERS) satellites, spanning from 1992 to 2001, and by the laser altimeter on NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) from 2003 to 2008.

Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods. They also used information on snow accumulation for tens of thousands of years, derived by other scientists from ice cores, to conclude that East Antarctica has been thickening for a very long time. 

“At the end of the last Ice Age, the air became warmer and carried more moisture across the continent, doubling the amount of snow dropped on the ice sheet,” Zwally said.

The extra snowfall that began 10,000 years ago has been slowly accumulating on the ice sheet and compacting into solid ice over millennia, thickening the ice in East Antarctica and the interior of West Antarctica by an average of 0.7 inches (1.7 centimeters) per year. This small thickening, sustained over thousands of years and spread over the vast expanse of these sectors of Antarctica, corresponds to a very large gain of ice – enough to outweigh the losses from fast-flowing glaciers in other parts of the continent and reduce global sea level rise.  

Zwally’s team calculated that the mass gain from the thickening of East Antarctica remained steady from 1992 to 2008 at 200 billion tons per year, while the ice losses from the coastal regions of West Antarctica and the Antarctic Peninsula increased by 65 billion tons per year.

“The good news is that Antarctica is not currently contributing to sea level rise, but is taking 0.23 millimeters per year away,” Zwally said. “But this is also bad news. If the 0.27 millimeters per year of sea level rise attributed to Antarctica in the IPCC report is not really coming from Antarctica, there must be some other contribution to sea level rise that is not accounted for.”

“The new study highlights the difficulties of measuring the small changes in ice height happening in East Antarctica,” said Ben Smith, a glaciologist with the University of Washington in Seattle who was not involved in Zwally’s study.

"Doing altimetry accurately for very large areas is extraordinarily difficult, and there are measurements of snow accumulation that need to be done independently to understand what’s happening in these places,” Smith said. 

To help accurately measure changes in Antarctica, NASA is developing the successor to the ICESat mission, ICESat-2, which is scheduled to launch in 2018. “ICESat-2 will measure changes in the ice sheet within the thickness of a No. 2 pencil,” said Tom Neumann, a glaciologist at Goddard and deputy project scientist for ICESat-2. “It will contribute to solving the problem of Antarctica’s mass balance by providing a long-term record of elevation changes.”

Mass changes of the Antarctic ice sheet impact sea-level rise as climate changes, but recent rates have been uncertain. Ice, Cloud and land Elevation Satellite (ICESat) data (2003–08) show mass gains from snow accumulation exceeded discharge losses by 82 ± 25 Gt a–1, reducing global sea-level rise by 0.23 mm a–1. European Remote-sensing Satellite (ERS) data (1992–2001) give a similar gain of 112 ± 61 Gt a–1. Gains of 136 Gt a–1 in East Antarctica (EA) and 72 Gt a–1 in four drainage systems (WA2) in West Antarctic (WA) exceed losses of 97 Gt a–1 from three coastal drainage systems (WA1) and 29 Gt a–1 from the Antarctic Peninsula (AP). EA dynamic thickening of 147 Gt a–1 is a continuing response to increased accumulation (>50%) since the early Holocene. Recent accumulation loss of 11 Gt a–1 in EA indicates thickening is not from contemporaneous snowfall increases. Similarly, the WA2 gain is mainly (60 Gt a–1) dynamic thickening. In WA1 and the AP, increased losses of 66 ± 16 Gt a–1 from increased dynamic thinning from accelerating glaciers are 50% offset by greater WA snowfall. The decadal increase in dynamic thinning in WA1 and the AP is approximately one-third of the long-term dynamic thickening in EA and WA2, which should buffer additional dynamic thinning for decades.

Source:

http://www.reportingclimatescience.com/news-stories/article/nasa-antarctica-is-not-melting-land-ice-is-growing.html

Mass gains of the Antarctic ice sheet exceed losses by Zwally, H. Jay; Li, Jun; Robbins, John W.; Saba, Jack L.; Yi, Donghui; Brenner, Anita C.published in Journal of Glaciology, DOI: 10.3189/2015JoG15J071