Antarc­tica ice loss has tripled in 5 years, threat­en­ing coast­lines

Shanghai Daily - - WORLD - (AFP)

ANTARC­TICA has lost a stag­ger­ing 3 tril­lion tons of ice since 1992, ac­cord­ing to a land­mark study pub­lished Wed­nes­day that sug­gests the frozen con­ti­nent could re­draw Earth’s coast­lines if global warm­ing con­tin­ues unchecked.

Two-fifths of that ice loss oc­curred in the last five years, a three-fold in­crease in the pace at which Antarc­tica is shed­ding its kilo­me­ters-thick cas­ing, a con­sor­tium of 84 sci­en­tists re­ported in the jour­nal Na­ture.

The find­ings should dis­pel any lin­ger­ing doubts that the con­ti­nent’s ice mass is shrink­ing, the au­thors said.

They also high­light the ex­is­ten­tial threat fac­ing low-ly­ing coastal cities and com­mu­ni­ties home to hun­dreds of mil­lions of peo­ple.

“We now have an un­equiv­o­cal pic­ture of what’s hap­pen­ing in Antarc­tica,” said co-lead au­thor Eric Rig­not, a sci­en­tist at NASA’s Jet Propul­sion Lab­o­ra­tory who has been track­ing Earth’s ice sheets for two decades.

Up to now, sci­en­tists have strug­gled in de­ter­min­ing whether Antarc­tica has ac­cu­mu­lated more mass through snow­fall than it loses in melt­wa­ter run-off and ice flows into the ocean.

But more than two decades of satel­lite data — the new find­ings draw from 24 sep­a­rate space-based sur­veys — have yielded a more com­plete pic­ture.

Cov­er­ing twice the area of the con­ti­nen­tal US, Antarc­tica is blan­keted by enough ice pack to lift global oceans by nearly 60 me­ters.

More than 90 per­cent of that frozen wa­ter sits atop East Antarc­tica, which has re­mained mostly sta­ble even as cli­mate change has driven up Earth’s av­er­age sur­face tem­per­a­ture by a full de­gree Cel­sius.

Some stud­ies had sug­gested a net gain in mass over re­cent decades.

West Antarc­tica, how­ever, has proven far more vul­ner­a­ble to global warm­ing, es­pe­cially the Antarc­tic Penin­sula, where more than 6,500 square kilo­me­ters of ice shelves have sheared off into the sea since 1995.

Al­ready float­ing, ice shelves break­ing off into ice­bergs do not add to sea level. But mas­sive glaciers on West Antarc­tica slowly glid­ing sea­ward hold enough wa­ter to push oceans up by 3.5 me­ters.

Two of these glaciers — Pine Is­land and Th­waites — have ac­cel­er­ated and are to­day seen as un­sta­ble. To­gether, they act as corks hold­ing back ice mass fur­ther in­land from fall­ing into the ocean.

Nearly all of the mass shed over the last quar­ter cen­tury has come from West Antarc­tica, the study found.

Ice loss of 2.7 tril­lion tons since 1992 added about 8 mil­lime­ters to sea level.

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