"The increasing mass loss that they're finding is really worrying, particularly looking at the West Antarctic, the area that's changing most rapidly and it's the area that we're most anxious about, because it's below sea level, " said Christine Dow, a glaciologist at the University of Waterloo in Canada who was not involved in the research. Since then, however, the melt rate has increased dramatically from an average of about 84 billion tons a year between 1992 and 2011, to more than 241 billion tons a year from 2012 to 2017.
At the rate that Antarctica is melting, the sea level could rise by 15 centimeters or six inches by 2100 - enough to flood Brooklyn 20 times per year, according to Shepherd.
By mapping our measured sea level contribution on top of these projections, we found that our previous assessment of Antarctic sea level contribution, which measured ice loss until 2012, was tracking the IPCC's lowest projection.
"Based on this evidence from the Pliocene, today's current carbon dioxide levels are not enough to destabilize the land-based ice on the Antarctic continent", said Jeremy Shakun, an assistant professor of Earth and Environmental Science at Boston College and a lead author on the paper.
Researchers say floating ice-shelf loss has triggered the faster loss of West Antarctic ice. Ice shelf collapse in the Antarctic Peninsula is another major contributor, whereas less certain estimates of East Antarctica's mass change suggest the region may have gained a negligible amount of ice.
Between 60 per cent and 90 per cent of the world's fresh water is frozen in the ice sheets of Antarctica, a continent roughly the size of the United States and Mexico combined. Coastal communities along the USA could feel the impact of a continued increase as melting ice adds to sea level rise, say experts.
Ekwurzel at the Union of Concerned Scientists said the study's findings mean "we have to go back and tell coastal planners that it may be worse than scientists thought before". The melting is the result of warmer ocean waters undermining glaciers grounded on sea bottoms around Antarctica and increased surface melt from warmer air temperatures.
"The next piece of the puzzle is to understand the processes driving this change", Durham University's Pippa Whitehouse said. However, a period of heavy snowfall between 2005 and 2010 masked some of the immediate effects of the ice loss, accounting for the sudden, steep increase in more recent years.
"The satellite measurements tell us that the ice sheet is much more dynamic than we used to think", he said.
And the ice losses quickened to 219 billion tons a year since 2012, from 76 billion previously.
In 2017, that number had risen to 0.6mm per year.
Although the general trend was of reduction, there was some increase in ice cover in East Antarctica.
The study was conducted by a group of researchers as part of the Ice Sheet Mass Balance Inter-comparison Exercise, or IMBIE, and published today in the journal Nature.
Those signs help researchers to gauge the pace of ice retreat in Antarctica - estimated in the past to be about 164 feet (50 meters) each year - between glacial cycles, Shepherd said. You can see ice loss in that area over time in the video above. "Things are happening. They are happening faster than we expected". "The future of Antarctica is tied to that of the rest of the planet and human society", said Steve Rintoul, of the Centre for Southern Hemisphere Oceans Research in Hobart, Tasmania, and one of the research team.
The research was done by taking data from satellites that have been flying over the Antarctic region for 25 years. "And the ice sheet is now losing three times as much ice", Shepherd adds.