Part of Antarctica has begun thawing unusually fast, leaving scientists unsure whether a natural cycle or human-caused climate change is responsible. By Tim Radford

Antarctic glaciers once thought relatively stable are starting to melt. Evidence from a five-year satellite study of the frozen rivers on the southern Antarctic Peninsula now reveal that these are shedding ice at the rate of 60 cubic kilometres a year: altogether around 300 trillion litres of water has moved from the frozen continent to the oceans.

Bert Wouters of the University of Bristol, UK, and colleagues report in the journal Science  that they used data from two very different research satellites to confirm their findings.

The European Space Agency’s CryoSat-2 has been orbiting the polar world since April 2010, bouncing radar signals off the surface and measuring the return travel time. An examination of five years of results shows that the glacial surfaces are sinking, in some places by as much as four metres a year. There could be two reasons for that: either the snow is compacting or the ice is flowing faster.

But results from the US space agency Nasa’s GRACE mission – the acronym stands for Gravity Recovery and Climate Experiment – settle the matter. The mass of ice lost in the region is so large that it changes the local gravity field, and the changes in the sheer weight of 750 kilometres of glaciers in the region can be measured from space.

“To date, the glaciers added roughly 300 cubic km of water to the ocean. That’s the equivalent of the volume of nearly 350,000 Empire State Buildings combined,” Dr Wouters said.

“The fact that so many glaciers in such a large region suddenly started to lose ice came as a surprise to us. It shows a very fast response of the ice sheet: in just a few years the dynamic regime completely shifted.”

Melting maintained

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