Antarctica's melting ice sheet could retreat much faster than previously thought, new research suggests.
The evidence comes from markings on the seafloor off Norway that record the pull-back of a melting European ice sheet thousands of years ago.
Today, the fastest withdrawing glaciers in Antarctica are seen to retreat by up to 30m a day.
But if they sped up, the extra melt water would have big implications for sea-level rises around the globe.
Ice losses from Antarctica caused by climate change have already pushed up the surface of the world's oceans by nearly 1cm since the 1990s.
The researchers found that with the Norwegian sheet, the maximum retreat was more than 600m a day.
"This is something we could see if we continue with the upper estimates for temperature rise," explained Dr Christine Batchelor from Newcastle University, UK.
"Although, worryingly, when we did the equations to think about what would be needed to instigate such retreat in Antarctica, we actually found there are places where you could get similar pulses of withdrawal even under the basal melt rates we know are happening at the moment," she told BBC News.