Melting ice sheets fuelling sea-level rise, warns Nasa

Melting ice sheets in Antarctica and Greenland could overtake mountain glaciers as the main contributors to rising sea levels, US scientists say.

A study lasting nearly 20 years has revealed that huge amounts of melted ice are pouring into the oceans.

This extra volume of water is probably surpassing that from mountain glaciers and ice caps, which have also been disappearing over the same period of time. Eric Rignot, of Nasa’s Jet Propulsion Laboratory in Pasadena and the University of California at Irvine, said: “That ice sheets will dominate future sea level rise is not surprising – they hold a lot more ice mass than mountain glaciers.

“What is surprising is this increased contribution by the ice sheets is already happening.

“If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007. Our study helps to reduce uncertainties in near-term projections of sea level rise.”

Satellite observations over two decades have led to estimate that the ice sheets of Greenland and Antartica lost on average 475 billion tons of ice each year.

This would be enough to raise global sea levels by an average of 1.3mm (0.05ins) a year, Nasa said.

The study also found that the melting of the ice sheets was accelerating significantly, with each subsequent year seeing more ice being lost. Each year over the course of the study, the two ice sheets lost a combined average of 36.3 billion tons more than the year before.

The scientists estimated that if the current rate at which the ice sheets are melting continues for the next four decades, the cumulative loss of ice could raise global sea levels by 15cm (5.9in) by 2050.

When this is added to the predicted sea level contribution of 8cm (3.1in) from glacial ice caps and 9cm (3.5in) from the thermal expansion of warmer seawater, the total sea level rise could reach 32cm (12.6in).

“While this provides one indication of the potential contribution ice sheets could make to sea level in the coming century, the authors caution that considerable uncertainties remain in estimating future ice loss acceleration,” according to a Nasa statement.

Isabella Velicogna, of Nasa’s Jet Propulsion Laboratory, said: “These are two totally independent techniques, so it is a major achievement that the results agree so well.

“It demonstrates the tremendous progress that is being made in estimating how much ice the ice sheets are gaining and losing and in analysing Grace’s time-variable gravity data.”

The study is to be published in the latest issue of the journal Geophysical Research Letters.

http://www.independent.co.uk/environment/climate-change/melting-ice-sheets-fuelling-sealevel-rise-warns-nasa-2237616.html