According to a new study by the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE), now considered to be the most complete and up-to-date picture of the changes happening to the Antarctic ice sheet, satellites had been recording a fairly steady rate of ice loss from Antarctica, of around 76 billion tonnes per year, between 1992 and 2012. However, ice retreat today is about more than 20 times that rate - more than 3,200 feet (1 kilometer) per year.
"Some of the changes Antarctica will face are already irreversible, such as the loss of some ice shelves, but there is a lot we can prevent or reverse", said Martin Siegert, study co-author and professor at the Grantham Institute in London.
Scientists have acknowledged that these sad results surpassed their expectations.
"We took all the estimates across all the different techniques, and we got this consensus", Isabella Velicogna, an Antarctic ice expert at the University of California at Irvine, told The Washington Post.
They include Antarctic glaciers speeding up in the wake of ice shelf collapse, warming waters in the Amundsen sea-which lies to the west of the continent-and reduced ice sheet growth in East Antarctica. In light of the acceleration in ice loss we have observed over the past five years, we now find sea level rise from Antarctica to be tracking the IPCC's highest projection. Geological evidence indicates that some marine-based portions of the East and West Antarctic Ice Sheets retreated during parts of the Pliocene, but it remains uncertain whether ice grounded above sea level also experienced retreat.
The East Antarctic Ice Sheet is one of three major ice sheets closely watched by scientists as global temperatures and carbon dioxide levels increase, glaciers melt and sea levels rise.
The largest ice sheet on Earth was stable throughout the last warm period in geologic time, indicating it should hold up as temperatures continue to rise.
Covering twice the area of the continental United States, Antarctica is blanketed by enough ice pack to lift global oceans by almost 60 metres (210 feet). But clues from the geologic record suggest that the climate change driving ice loss in Antarctica is doing so much faster than during its periods of ice loss in the distant past, Shepherd told Live Science.
Regardless of the exact rate, these findings emphasize the importance of efforts to combat climate change.
Antarctica is one of the world's fastest-warming regions. Sea level rise is a threat to cities from NY to Shanghai as well as low-lying nations from the Pacific Ocean to the Netherlands.
From 1992 to 2012, sea levels were said to be rising at an average of 0.2mm each year due to ice loss.
"If you take a look at the first IPCC [Intergovernmental Panel on Climate Change] assessment report - 30 years ago, before we had satellite measurements of the polar regions - you'll see that the ice sheets were not expected to respond to climate change at all".
That might not sound like much, but what's particularly concerning is the way the ice loss has sharply accelerated over the course of the 25-year timeframe. "The good news is that limited climate change can slow the rate of ice loss, and there are many proven actions that can reduce climate change and be implemented immediately. And the ice sheet is now losing three times as much ice", Shepherd adds.
Antarctica's ice sheet is melting at rapidly increasing rate, now pouring more than 200 billion tons of ice into the ocean annually and raising sea levels a half millimeter every year, a team of 80 scientists reported Wednesday. "This has to be a concern for the governments we trust to protect our coastal cities and communities", said Shephard.