Sea lev­els may rise more rapidly due to Green­land ice melt

The Guardian Australia - - Environment - Jonathan Watts Global en­vi­ron­ment ed­i­tor

Ris­ing sea lev­els could be­come over­whelm­ing sooner than pre­vi­ously be­lieved, ac­cord­ing to the au­thors of the most com­pre­hen­sive study yet of the ac­cel­er­at­ing ice melt in Green­land.

Run-off from this vast north­ern ice sheet – cur­rently the big­gest sin­gle source of melt­wa­ter adding to the vol­ume of the world’s oceans – is 50% higher than pre-in­dus­trial lev­els and in­creas­ing ex­po­nen­tially as a re­sult of man­made global warm­ing, says the pa­per, pub­lished in Na­ture on Wed­nes­day.

Al­most all of the in­crease has oc­curred in the past two decades – a jolt up­wards af­ter sev­eral cen­turies of rel­a­tive sta­bil­ity. This sug­gests the ice sheet be­comes more sen­si­tive as tem­per­a­tures go up.

“Green­land ice is melt­ing more in re­cent decades than at any point in at least the last four cen­turies, and prob­a­bly more than at any time in the last seven to eight mil­len­nia,” said the lead au­thor Luke Trusel, of Rowan Univer­sity.

“We demon­strate that Green­land ice is more sen­si­tive to warm­ing to­day than in the past – it re­sponds non-lin­early due to pos­i­tive feed­backs in­her­ent to the sys­tem. Warm­ing means more to­day than it did even just a few decades ago.”

The re­searchers used ice core data from three lo­ca­tions to build the first multi-cen­tury record of tem­per­a­ture, sur­face melt and run-off in Green­land. Go­ing back 339 years, they found the first sign of melt­wa­ter in­crease be­gan along with the in­dus­trial rev­o­lu­tion in the mid-1800s. The trend re­mained within the nat­u­ral vari­a­tion un­til the 1990s, since when it has spiked far out­side of the usual nine- to 13-year cy­cles.

Green­land cur­rently con­trib­utes about 20% of global sea-level rise, which is run­ning at 4mm per year. This pace will prob­a­bly dou­ble by the end of the cen­tury, ac­cord­ing to the most re­cent mod­els used by the UN In­ter­gov­ern­men­tal Panel on Cli­mate Change. How the new study af­fects those pro­jec­tions will be the sub­jects of fu­ture study by the au­thors. If all the ice in Green­land melted, it would raise sea lev­els by seven me­tres. At the cur­rent pace that would take thou­sands of years, but the on­go­ing ac­cel­er­a­tion could bring this for­ward rapidly.

“At some point, sea-level rise will be too fast for us to adapt to, so we re­ally have to avoid this sit­u­a­tion by re­duc­ing emis­sions,” said the study’s co-au­thor Michiel van den Broeke of Utrecht Univer­sity. “I think this is one of the many wake-up calls that we have had in the last few decades. It clearly links man­made global warm­ing to sealevel rise.”

The re­search comes out as pol­i­cy­mak­ers from around the world are at­tend­ing UN cli­mate talks in Ka­tow­ice, Poland, where gov­ern­ments are try­ing to set new rules to keep global warm­ing to be­tween 1.5C and 2C. The au­thors said the pa­per un­der­lined the dan­gers of ex­ceed­ing even the lower fig­ure.

“On a per­sonal level it is wor­ry­ing to see this – along with the vast ar­ray of other sci­en­tific ev­i­dence show­ing that we’ve en­tered un­prece­dented or ex­cep­tional times,” said Trusel.

“The ice has no po­lit­i­cal agenda – it ei­ther grows or melts. To­day it is melt­ing as hu­mans have warmed the planet. The ice sheets have tip­ping points, and how quickly they im­pact our liveli­hoods through sea level rise de­pends on what we do now and in the very near fu­ture.”

Other aca­demics, un­in­volved in the pa­per, said the new study was an im­por­tant con­fir­ma­tion of what sci­en­tists have long sus­pected: that the re­cent in­crease in ice melt is omi­nously un­usual.

“The Green­land ice sheet is like a sleep­ing gi­ant who is slowly but surely awak­en­ing to on­go­ing global warm­ing, and there are sur­prises in its re­sponse. How­ever, the re­sponse may be more rapid than pre­vi­ously be­lieved,” said Ed­ward Hanna, pro­fes­sor of cli­mate science and me­te­o­rol­ogy at the Univer­sity of Lincoln.

Pho­to­graph: Sarah Das/Woods Hole Oceano­graphic In­sti­tu­tion/PA

A melt­wa­ter canyon on the Green­land ice sheet.

Newspapers in English

Newspapers from Australia

© PressReader. All rights reserved.