Mass Gains Of Antarctic Ice Sheet Greater Than Losses
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.”
2 thoughts on “Mass Gains Of Antarctic Ice Sheet Greater Than Losses”
Perhaps sea level rise is not just solely added water, but debris and life. May sound ridiculous, but we should not discount all that is possible to enter our oceans. Space dust, garbage, added sea-life, continent erosion, and of course boats displace water too. Not that this is conclusive, just a thought.
Not mentioned is the increase over recent years of Himalayan ice mass or the huge increase in the north polar ice mass the winter before last. These may be just aberrations like the shrinking of glaciers in other parts of the world or they may both be examples of incomplete data. The fact remains that global temperatures have been decreasing over a number of years, despite the tweaking of data by environmental authorities in their models and theoretical guesstimates of values in those models for possibly self-serving reasons. Sea levels could be rising slightly for other reasons; the most obvious that comes to mind is the massive deforestation of large areas on earth in the last century. Forests are responsible for the storage of vast quantities of fresh water, which, if not stored is released into the seas. Let’s not forget that trees have increased their ability to convert CO2 into O2 during the period over which climate studies have gained influence as a type of science; possibly as an adaptation to us. We would do well to spend our limited global resources on things over which we can have more direct and quantitative influence in the short term and while supporting the commercial evolution of effective energy alternatives to fossil fuels, perhaps wait until we have better data before gutting our 1st world economies in the name of climate change.
I read a history of the settlement of parts of Greenland around 1000 AD by a large population of Scandinavians who farmed and raised livestock there. Their efforts at harvesting large sea mammals met with limited success due to their failure to adopt the hunting methods and watercraft of the native peoples. The Scandinavians were supported by commerce with their homelands, but over the next few centuries the earth cooled as it moved toward a mini ice age and the settlers died off, because of shorter growing seasons, competition for game with the better-adapted natives and an inability to get through the ocean ice to reach their homelands for support. We would do well to remember that climate does indeed change in different directions and for more reasons than we may yet have a firm grasp on.