Sea lev­els to rise as melt­ing of ice sheets con­tin­ues

Western Daily Press - - Uk & World News - EMILY BEA­MENT Press As­so­ci­a­tion

THE melt­ing of Green­land’s ice sheet has ac­cel­er­ated to un­prece­dented rates in the face of ris­ing tem­per­a­tures, anal­y­sis of ice cores has found.

Sur­face melt­ing across the the mile-thick ice sheet in­creased in the 19th cen­tury as hu­man ac­tiv­ity started to warm the cli­mate, but ramped up in the 20th and early 21st cen­turies and shows no signs of abat­ing, sci­en­tists said.

Ice loss from Green­land, in­clud­ing runoff from melted snow and ice on the top of the ice sheet, is con­tribut­ing to sea level rises.

If Green­land ice con­tin­ues to melt at un­prece­dented rates as a re­sult of warmer sum­mers, it could ac­cel­er­ate the al­ready fast pace of sea level rise, the re­searchers warned.

Anal­y­sis of ice core sam­ples from sites 6,000ft (1,829m) above sea level has en­abled the re­searchers to as­sess melt­ing dat­ing back 350 years.

The ice cores con­tain lay­ers that show how ice melted and re­froze on con­tact with the snow-pack un­der­neath each year, re­veal­ing the in­ten­sity of melt­ing.

The sci­en­tists com­bined the re­sults from ice cores with satel­lite data and cli­mate mod­els to re­con­struct melt-wa­ter runoff at lower el­e­va­tions on the edge of the ice sheet that con­trib­utes to sea level rise.

They found that in­creases in melt­ing closely fol­low the start of in­dus­trial-era warm­ing in the Arc­tic in the mid-1800s but the mag­ni­tude of the melt has ex­ceeded nat­u­ral vari­abil­ity in the past few decades.

Study co-au­thor Sarah Das, from Woods Hole Oceano­graphic In­sti­tu­tion in the US, said: “From a his­tor­i­cal per­spec­tive, to­day’s melt rates are off the charts, and this study pro­vides the ev­i­dence to prove this.”

To­tal ice sheet melt-wa­ter runoff had in­creased 50% com­pared with the start of the in­dus­trial era, and had seen a 30% in­crease since the 20th cen­tury alone, she said.

Sum­mer melt­ing in 2012 was at lev­els that rep­re­sented “ex­cep­tional highs” for the past 350 years.

And melt and runoff in the last decade are likely to be un­prece­dented in the past 6,800 to 7,800 years, a study pub­lished in the jour­nal Na­ture showed.

The re­searchers also warned that Green­land, which locks up the equiv­a­lent of around 30ft (7m) of sea level rise, is be­com­ing more sen­si­tive to warm­ing than it was in the past.

The world has al­ready warmed by al­most 1C since pre-in­dus­trial times, and there are con­cerns that the ice sheet could reach a tip­ping point at around 1.5C to 2C of warm­ing, lead au­thor Luke Trusel said.

At that point it could go into a state of ir­re­versible re­treat.

Dr Trusel said: “We see melt­ing and runoff from Green­land start tick­ing up as warm­ing ini­ti­ated in the Arc­tic in the 1800s, but only in the last few decades has it re­ally ac­cel­er­ated to lev­els we haven’t seen be­fore in the last few cen­turies.”

He said melt­ing had gone “into over­drive”, and as a re­sult Green­land melt was adding to sea level more than any time dur­ing the last three­and-a-half

cen­turies, if not thou­sands of years.

As the ice sheet melts it be­comes slightly darker, ab­sorb­ing more sun­light and melt­ing more, even if tem­per­a­tures do not change, while in­creased melt­ing can gen­er­ate im­per­me­able ice lay­ers which ex­ac­er­bate runoff.

Dr Trusel, from Rowan Univer­sity’s School of Earth and En­vi­ron­ment in New Jersey, US, said Green­land would melt more and more for ev­ery de­gree of warm­ing.

“The melt­ing and sea level rise we’ve ob­served al­ready will be dwarfed by what may be ex­pected in the fu­ture as cli­mate con­tin­ues to warm,” he said.

Mean­while the UK Met Of­fice has said that cli­mate change made this year’s sum­mer heat­wave around 30 times more likely than it would be un­der nat­u­ral con­di­tions.

This sum­mer was the equal warm­est in a se­ries dat­ing back to 1910, along with 2006, 2003 and 1976, with tem­per­a­tures reach­ing a peak on July 27 when 35.6C (96F) was recorded at Felsham, Suf­folk.

New anal­y­sis from the has found that the record-break­ing sum­mer tem­per­a­tures were about 30 times more likely as a re­sult of cli­mate change caused by hu­man ac­tiv­i­ties.

The UK now has around a 12% chance of sum­mer av­er­age tem­per­a­tures be­ing as high as they were in 2018, whereas they would have less than 0.5% chance of hap­pen­ing in a “nat­u­ral” cli­mate

Sarah Das/Woods Hole Oceano­graph

Melt­wa­ter on Green­land’s ice-sheet

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