Ice losses are spreading fast deep in the interior of Antarctica, new analysis of satellite data shows.
Global warming is causing glaciers to sink into the sea faster and faster, with ice now being lost five times faster than in the 1990s. The ice sheet of West Antarctica was stable in 1992, but is now dropping to a quarter of its vastness. More than 100 meters of ice thickness was lost in the most affected places.
A complete loss of the West Antarctic ice sheet would raise global sea level by about five meters, drowning coastal cities around the world. The current losses double every decade, scientists say, and the sea level rise is now running at the end of the projections made a few years ago.
The research, published in the journal Geophysical Research Letters, compared 800m satellite measurements of the ice sheet height between 1992 and 2017 with weather information. These distinctive short-term changes due to changing snowfall due to long-term changes due to the climate.
"From the beginning of the 1990s, thinning has gradually increased inland over the last 25 years – that is fast in glaciological terms," said Prof. Andy Shepherd of the University of Leeds in Great Britain, who led the study. "In the past people talked about the speed at which ice was pulled from an ice cap in geological timescales, but it has now been replaced by people's lives."
He said that the thinning of some ice flows had extended 300 miles inland along their 600-mile length. "More than 50% of the Pine Island and Thwaites glacier basins have been weakened by dilution over the past 25 years. We are halfway through and that is a concern."
Researchers already knew that ice was lost from West Antarctica, but the new work indicates where it takes place and how quickly. This will make it possible to make more accurate projections of sea level rises and can help prepare for these rises.
In the recent past, the snow that fell on the glaciers of Antarctica balanced the ice that was lost when icebergs came into the ocean. But now the glaciers flow faster than snow can fill them up.
"Along a 3,000 km [1,850-mile] piece of West Antarctica, the water for the glaciers is too hot, "he said. This causes the bottom of the glaciers to melt where they grind against the seabed. The melting reduces friction and leaves the glaciers in the ocean faster and therefore becomes thinner.
"In parts of Antarctica, the ice sheet has been thinned by extraordinary amounts," Shepherd said.
Separate research published in January showed that the loss of ice from the entire Antarctic continent had increased six-fold since the 1980s, with the largest losses in the West. The new study indicates that West Antarctica has caused a 5 mm rise in sea level since 1992, in accordance with the findings of the January study.
The expansion of the oceans as they warm up and the huge melting in Greenland are the main current causes of the rising oceans, but Antarctica is the largest supply of ice. The East Antarctic ice sheet contains enough ice to raise the sea level by approximately 60 meters. It was considered stable, but research in December showed that even this stronghold shows signs of melting.
Without rapid cuts in carbon emissions that affect global warming, the melting and rising sea level will continue for thousands of years.
"Before we had useful satellite measurements from space, most glaciologists thought the polar ice creams were quite isolated from climate change and did not change at all," Shepherd said. "Now we know that's not true."