Satellite measurements have confirmed Antarctica is losing land-bound ice to climate change, ending years of uncertainty.
A milestone study has pinpointed the total contribution to sea-level rise of melting in the Earth's main ice sheets.
Until now the spread of possible scenarios by the Intergovernmental Panel on Climate Change meant it was impossible to say whether Antarctic ice sheets were growing or shrinking.
The study published in the US journal Science on Friday shows Antarctica losing a net 71 billion tonnes of ice each year - but still being vastly outpaced by the rate of ice loss in Greenland. There, about 152 billion tonnes of ice annually is turning to water.
"The importance of this work should not be understated," said Professor Matt King, of the University of Tasmania, part of a team led by the University of Leeds' Andrew Shepherd.
"This really is the first time the scientific community has reached consensus that Antarctica is losing mass, and hence raising sea levels," Professor King said. "But it's not losing mass anywhere near as fast as Greenland is."
The study found that in the past 20 years, combined losses from the ice sheets accounted for 11.1 millimetres, or about a fifth, of global sea-level rise. Expansion of heating seawater and the loss of continental waters also play strong roles in this increase.
The study discovered that between them, the Greenland and Antarctic ice sheets were now losing three times as much ice each year, as in the 1990s.
Professor King said Antarctic ice losses could well accelerate further into the future.
“The sea-level change we're seeing today is happening faster than it has for centuries with just a small contribution from the massive Antarctic ice sheet.
"What is sobering is that sea levels will rise even faster if Antarctica continues to lose increasingly more ice into the oceans.”
In the study, the Ice Sheet Mass Balance Inter-Comparison, a group of 47 international researchers, collected data including satellite radar altimeter, laser altimeter, and gravity measurements to reach their conclusion.
Professor King worked on gravity measurements from NASA's GRACE satellite, but warned this mission was nearing its end, and another key ice watching satellite, IceSat, had stopped working.
"Continuations of these sorts of missions, and field observations in Antarctica are really critical," he said. "But there is a strong chance there will be a data gap."
He said there was a particular need for scientists to focus on East Antarctica, which is mainly claimed by Australia. "Ice mass change (there) is even now not entirely understood," he said.
Morning & Afternoon Newsletter