News in Science

Giant Antarctic glacier beyond point of no return

Thawing out Antarctica's Pine Island Glacier, one of the biggest single contributors to world sea-level rise, is melting irreversibly and could add as much as a centimetre to ocean levels in 20 years, say scientists.

The glacier "has started a phase of self-sustained retreat and will irreversibly continue its decline," says Gael Durand, a glaciologist with France's Grenoble Alps University.

Durand and an international team used three different models to forecast the glacier's future based on the "grounding line," which is the area under water where the ice shelf - a sea-floating extension of the continent-covering ice sheet - meets land.

This line has receded by about 10 kilometres in the past decade.

The grounding line "is probably engaged in an unstable 40 kilometre retreat," according to the study, published in the journal Nature Climate Change.

A massive river of ice, the glacier by itself is responsible for 20 per cent of total ice loss from the West Antarctic Ice Sheet today.

On average, it shed 20 billion tonnes of ice annually from 1992-2011, a loss that is likely to increase up to and above 100 billion tonnes each year, the study's authors write.

This is equivalent to 3.5 to 10 millimetres of global average sea-level rise over the next 20 years.

The global mean sea level rose by 3.2 millimetres in 2010 - itself a near-doubling from the rate of two decades earlier.

The European Space Agency said last month that the West Antarctic ice sheet was shedding ice at a much faster rate than before - currently at about 150 cubic kilometres per year.

Climate scientists are keeping a worried eye on the mighty ice sheets of Greenland and Antarctica, as continued losses could threaten vulnerable coastal cities with dangerously high sea levels.

Last year, the United Nations' climate science body, the Intergovernmental Panel on Climate Change (IPCC) projected sea levels would rise between 26 and 82 centimetres by 2100.