Study says 92 billion tons of ice melting each year
FRISCO — Sparse data make it tough to track continental-scale climatic changes across the vast reaches of Antarctica. But a new study that analyzed gravitational readings from satellites is helping scientists understand what’s happening to the region’s massive ice fields, and in a new study, they say that, overall, the southern continent’s ice cap is melting ever faster.
The study covers a 10-year span, from 2003 to 2014, when an average of 92 billion tons of ice melted away into the sea each year, with obvious implications for sea level rise. Reporting in the journal Earth and Planetary Science Letters, the Princeton researchers said that, if all that ice were piled on Manhattan it would be more than a mile high, five times the height of the Empire State Building.
Ten years worth of data didn’t enable the scientists to establish a conclusive link between the melting and human-caused global warming, “But with the rapidly accelerating rates at which the ice is melting, and in the light of all the other, well-publicized lines of evidence, most scientists would be hard pressed to find mechanisms that do not include human-made climate change,” said Frederik Simons, a Princeton associate professor of geosciences.
The study concluded that most of the melting is in West Antarctica, close to the distinctive Antarctic Peninsula, which spikes toward South America. In this region the annual rate of ice loss has doubled since 2008, from 121 billion tons to about 240 billion tons annually by 2014.
The East Antarctica thickened slightly during that time, but not enough to make for the losses from the West, showing that the western ice sheet is much more unstable compared to other regions of the continent. Overall, ice-loss rates from all of Antarctica increased by 6 billion tons per year each year during the 11-year period, with the melting rate from West Antarctica growing by 18 billion tons each year.
Researcher Christopher Harig took an especially close look at the Amundsen Sea area, where heavy losses had already been recorded. In 2002, an iceberg more than 2,000 square miles in size broke off from the Thwaites Glacier.
Other studies have shown that ocean currents are the primary force that’s driving ice loss in Antarctica, rather than air temperatures. As the ocean warms, floating ice shelves melt and can no longer hold back the land ice, which is the big contributor to sea level rise.
“The fact that West Antarctic ice-melt is still accelerating is a big deal because it’s increasing its contribution to sea-level rise,” Harig said. “It really has potential to be a runaway problem. It has come to the point that if we continue losing mass in those areas, the loss can generate a self-reinforcing feedback whereby we will be losing more and more ice, ultimately raising sea levels by tens of feet.”
The Princeton study measured the mass of ice rather than its volume, using data from the Gravity Recovery and Climate Experiment (GRACE), a dual-satellite joint mission between NASA and the German Aerospace Center. GRACE measures gravity changes to determine the time-variable behavior of various components in the Earth’s mass system such as ocean currents, earthquake-induced changes and melting ice.
Ice sheet volume can change without affecting the amount of ice that is present, Simons explained. Snow and ice, for instance, compact under their own weight so that to the lasers that are bounced off the ice’s surface to determine volume, there appears to be a reduction in the amount of ice, Simons said.
Mass or weight, on the other hand, changes when ice is actually redistributed and lost. Simons equated the difference between measuring ice volume and mass to a person weighing himself by only looking in the mirror instead of standing on a scale.
“You shouldn’t only look at the ice volume … you should also weigh it to find the mass changes,” Simons said. “But there isn’t going to be a whole lot of research of this type coming up because the GRACE satellites are on their last legs. This could be the last statement of this kind on these kinds of data for a long time. There may be a significant data gap during which the only monitoring available will not be by ‘weighing’ but by ‘looking’ via laser or radar altimetry, photogrammetry or field studies.”