Study blames humans for most of melting glaciers

Global warming is the leading culprit; soot pollution, land use also play a role

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WASHINGTON — More than two-thirds of the re­cent rapid melt­ing of the world’s gla­ciers can be blamed on hu­mans, a new study finds.

Sci­en­tists look­ing at gla­cier melt since 1851 didn’t see a hu­man fin­ger­print un­til about the mid­dle of the 20th cen­tury. Even then, only one-quar­ter of the warm­ing wasn’t from nat­u­ral causes.

But since 1991, about 69 per­cent of the rap­idly in­creas­ing melt was man-made, said Ben Mar­zeion, a cli­mate sci­en­tist at the Univer­sity of Inns­bruck in Aus­tria. “Glaciers are re­ally shrink­ing rap­idly now,” he said. “I think it’s fair to say most of it is man-made.”

Sci­en­tists fault global warm­ing from the burn­ing of coal, oil and gas as well as changes in land use near gla­ciers and soot pol­lu­tion. Glaciers in Alaska and the Alps in gen­eral have more hu­man-caused melt­ing than the global av­er­age, Mr. Mar­zeion said.

The study was pub­lished Thurs­day in the jour­nal Science.

The re­search is the first to cal­cu­late just how much of the gla­cial melt­ing can be at­trib­uted to peo­ple, and “the jump from about a quar­ter to roughly 70 per­cent of to­tal gla­cier mass loss is sig­nifi­cant and con­cern­ing,” said Univer­sity of Alaska Fair­banks geo­phys­i­cist Regine Hock, who wasn’t part of the study.

Over the last two de­cades, about 295 bil­lion tons (269 bil­lion met­ric tons) of ice is melt­ing each year on av­er­age due to hu­man causes and about 130 bil­lion tons (121 mil­lion met­ric tons) a year are melt­ing be­cause of nat­u­ral causes, Mr. Mar­zeion cal­cu­lated.

Glaciers alone add to about four-tenths of an inch of sea level rise ev­ery de­cade, along with even-big­ger in­creases from melt­ing ice sheets — which are dif­fer­ent than gla­ciers — and the ex­pan­sion of wa­ter with warmer tem­per­a­tures.

Mr. Mar­zeion and col­leagues ran mul­ti­ple com­puter sim­u­la­tions to see how much melt­ing there would be from all causes, and then did it again to see how much melt­ing there would be if only nat­u­ral causes were in­cluded. The dif­fer­ence is what was caused by hu­mans.

Sci­en­tists aren’t quite cer­tain what nat­u­ral causes started gla­ciers shrink­ing af­ter the end of the Lit­tle Ice Age in the mid­dle of the 19th cen­tury, but do know what are hu­man-causes: cli­mate change, soot and lo­cal changes in land use.

There is a siz­able mar­gin of er­ror, so the 69 per­cent hu­man-caused can be as low as 45 per­cent or as high as 93 per­cent, but likely in the mid­dle.

“This study makes per­fect sense,” said Penn­syl­va­nia State Univer­sity gla­cier ex­pert Rich­ard Al­ley, who wasn’t part of the re­search. “The au­thors have quan­ti­fied what I be­lieve most sci­en­tists would have ex­pected.”

Not all of the hu­man-caused melt­ing is from global warm­ing from the burn­ing of fos­sil fu­els, but cli­mate change is the big­gest fac­tor, said Ted Scam­bos, a sci­en­tist at the Na­tional Snow and Ice Data Center.

The study showed that it took time for global warm­ing and other fac­tors to build up and cause melt­ing. That lag ef­fect means the world is al­ready locked into more rapid melt­ing from the warm­ing that has al­ready oc­curred, Mr. Mar­zeion and Mr. Al­ley said.

United States - North America - Alaska


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