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Drastic speedup in Arctic melting forecast

Dec. 11, 2006
Courtesy National Center for Atmospheric Research
and World Science staff

Re­cent melt­ing of Arc­tic sea ice is like­ly to speed up so rap­id­ly that Arc­tic Ocean sum­mers could be near­ly ice-free as ear­ly as 2040, ac­cord­ing to new re­search.

A study pub­lished last year claimed that this would hap­pen by this cen­tu­ry’s end. Thus the new fore­cast moves the date for­ward a few decades.

Two frames from a sim­u­la­tion show­ing the ap­prox­i­mate ex­tent of Arc­tic sea ice in Sep­tem­ber. The top im­age  is from 2000; the bot­tom, from 2040. This is a like­ly sce­nar­i­o un­less green­house gas emis­sions are sig­nif­i­cant­ly cur­tailed, re­search­ers say. (Cour­te­sy NCAR)

The stu­dy, pub­lished in the Dec. 12 is­sue of the jour­nal Ge­o­phys­i­cal Re­search Let­ters, is by sci­en­t­ists from the U.S. Na­tion­al Cen­ter for At­mos­pher­ic Re­search in Boul­der, Co­lo., and oth­er in­s­ti­tu­tions.

The research an­a­lyzes the im­pact on the Arc­tic of “green­house gas” emis­sions. These are gases, inc­lu­d­ing car­bon di­ox­ide, pro­duced part­ly by hu­man ac­tiv­i­ties and be­lieved to be large­ly re­spon­si­ble for dra­ma­t­ic glo­b­al warm­ing in re­cent de­c­ades.

Sci­en­tists be­lieve the trend may lead to en­vi­ron­men­tal cat­a­clysm. The Arc­tic is one of the earl­iest re­gions af­fect­ed. Among other things, drown­ings of po­lar bears and wal­rus pups have been re­ported with the melt­ing of ice on which the an­i­mals live.

Su­per­com­puter sim­u­la­tions show that sea ice each Sep­tem­ber could shrink so ab­rupt­ly that, with­in two dec­ades, it may beg­in re­treat­ing four times fast­er than at any time in the ob­served rec­ord, the au­thors of the new stu­dy say.

“We have al­ready wit­nessed ma­jor losses in sea ice, but our re­search sug­gests that the de­crease over the next few decades could be far more dra­mat­ic than an­ything that has hap­pened so far,” said the cen­ter’s Marika Hol­land, lead au­thor of the stu­dy. “These changes are sur­pris­ing­ly rapid.”

Arc­tic sea ice has re­treated in re­cent years, es­pe­cial­ly in the late sum­mer, when ice is at a min­i­mum. 

The re­search team cited sev­er­al rea­sons for the ab­rupt loss of ice. Open wa­ter ab­sorbs more sun­light than does ice, so grow­ing re­gions of ice-free wa­ter would ac­cel­er­ate the warm­ing trend. And glob­al cli­mate change is ex­pected to in­flu­ence ocean cir­cu­la­tions and drive warm­er ocean cur­rents in­to the Arc­tic. It’s a “feed­back loop with dra­mat­ic im­pli­ca­tions for the en­tire Arc­tic re­gion,” Hol­land said.

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Recent melting of Arctic sea ice is likely to speed up so rapidly that Arctic Ocean summers could be nearly ice-free by early as 2040, according to new research. A study published last year claimed that this would happen by this century’s end. Thus the new forecast moves the date forward a few decades. The study, published in the December 12 issue of the journal Geophysical Research Letters, is by scientists from the U.S. National Center for Atmospheric Research in Boulder, Colo., and colleagues at other institutions. It analyzes the impact on the Arctic of “greenhouse gas” emissions. Such emissions, produced primarily by human activities, are believed to be largely responsible for dramatic global warming in recent decades. The most important greenhouse gas is carbon dioxide. Scientists believe the trend could lead to environmental cataclysm. The Arctic is especially affected, with drownings of polar bears and walruses reported with the melting of sea ice on which the animals live. Supercomputer simulations show that sea ice each September could shrink so abruptly that, within two decades, it may begin retreating four times faster than at any time in the observed record, the authors of the new study say. “We have already witnessed major losses in sea ice, but our research suggests that the decrease over the next few decades could be far more dramatic than anything that has happened so far,” said the center’s Marika Holland, leaud author of the study. “These changes are surprisingly rapid.” Arctic sea ice has retreated in recent years, especially in the late summer, when ice thickness and area are at a minimum. The research team poined to several reasons for the abrupt loss of ice in a gradually warming world. Open water absorbs more sunlight than does ice, meaning that the growing regions of ice-free water will accelerate the warming trend. And global climate change is expected to influence ocean circulations and drive warmer ocean currents into the Arctic. It’s a “feedback loop with dramatic implications for the entire Arctic region,” Holland said.