Antarctic ice may melt 20 times faster than we thought

The melting of the ice sheets in Antarctica may recede much faster than scientists thought. A study published April 5 in the journal Nature discovered that at the end of the last Ice Age, parts of the Eurasian ice sheet receded by up to 2,000 feet per day. This rate is 20 times faster than previous measurements. These changes far outpace even the fastest moving glaciers studied in Antarctica, which are estimated to be retreating as fast as 160 feet per day.

The new findings could be crucial to better understand current ice melt.

The Eurasian Ice Sheet was the third largest ice mass during the last Ice Age and retreated from Norway around 20,000 years ago. At its largest, it spanned nearly 3,000 miles. Reflecting these retreats are the ice sheets in Greenland and Antarctica, which have lost more than 6.4 trillion tons of ice in the last three decades. Both modern ice sheets are responsible for more than a third of the total rise in sea level.

“Our research provides a warning from the past about the rates at which ice sheets are physically capable of retreating,” Christine Batchelor, study co-author and a physical geographer at Newcastle University, said in a statement. “Our results show that rapid withdrawal pulses may be much faster than anything we’ve seen so far.”

[Related: We’re finally getting close-up, fearsome views of the doomsday glacier.]

For this study, an international team of researchers used high-resolution images of the seafloor to see how the ice sheet was changing. They mapped more than 7,600 small-scale landforms called “ripple ridges” on the seafloor around where the ice sheet once stood. The ridges are less than eight feet high and are between 82 and 984 feet apart. These types of ridges are thought to have formed when the ice sheet retreat margin moved with the tide. Seafloor sediments are pushed toward a ridge each low tide, so two ridges would have been produced during two daily tidal cycles. The space helped the team calculate the enormous speed of withdrawal.

This kind of data about how ice sheets reacted to past periods of warming can help inform computer simulations that predict future changes in ice cover and sea level. It also suggests that these periods of rapid melting may last only days to months, which are relatively short periods of time from a geological point of view.

“This shows how rates of ice sheet retreat averaged over several years or more can hide shorter bouts of more rapid retreat,” study co-author and University of Cambridge glaciologist Julian Dowdeswell said in a statement. “It is important that computer simulations can reproduce this behavior of the ‘pulsed’ ice sheet.”

[Related: Ice doesn’t always melt the same way—and these visuals prove it.]

Understanding these seafloor landforms also reveals the mechanics behind the rapid retreat of the ice. The study found that the old ice sheet retreated further across the flattest point of its bed where, “less melting is required to thin the overlying ice to the point where it starts to float,” explained co-author and glacier geophysicist Scott’s Cambridge Frazer Christie in a statement. “An ice margin can break away from the seafloor and retreat almost instantly when it becomes buoyant.”

The team believes similarly rapid receding pulses could soon be observed in some parts of Antarctica, including West Antarctica’s vast Thwaites Glacier. Nicknamed the “Doomsday Glacier,” Thwaites could be suffering from a similar pulse of rapid ice retreat, having recently retreated near a flat area of ​​its bed.

“Our findings suggest that current melt rates are sufficient to cause short pulses of rapid recoil in flat areas of the Antarctic ice sheet, including on Thwaites,” Batchelor said. “Satellites may well detect this style of ice sheet retreat in the near future, especially if we continue on our current trend of climate warming.”