Several of Antarctica's glaciers have already begun an unstoppable meltdown, two studies suggest.

Eric Rignot at the University of California, Irvine, and his colleagues used satellite radar to measure the retreat of five glaciers in West Antarctica and found that there is nothing holding the ice sheets back from catastrophic collapse, leaving them more vulnerable than previously thought. These glaciers hold enough water to raise the global sea level by 1.2 metres.

A team led by Ian Joughin at the University of Washington in Seattle modelled the behaviour of one of these glaciers, the Thwaites Glacier, and found that it is permanently destabilized. The melting of Thwaites will probably raise sea levels by 2.5 centimetres over the next century and by more than a millimetre per year within two to nine centuries, the team says.

Geophys. Res. Lett. http://doi.org/srf (2014); Science 344, 735–738 (2014)