Case closed, says study: CO2 melted Ice Age glaciers


Green­house gases were the driv­ing force be­hind global glacier re­treat at the end of the last Ice Age, echo­ing cur­rent cli­mate change, ac­cord­ing to a study pub­lished Fri­day.

More than 11,000 years later, the re­searchers say, global warm­ing is on track to wipe out 80-90 per­cent of re­main­ing glaciers within a few hun­dred years un­less car­bon diox­ide emis­sions are held in check.

Such an out­come would push sea level rise and rob hun­dreds of mil­lions of peo­ple in Asia and South Amer­ica of a crit­i­cal source of wa­ter.

Us­ing new tech­niques to re­solve an old de­bate, re­searchers showed that it was a 55-per­cent in­crease of CO2 in the at­mos­phere — from 180 to 280 parts per mil­lion (ppm) — over some 7,000 years that melted the world’s glaciers to a level that re­mained sta­ble un­til the start of our in­dus­trial era.

Higher lev­els of green house gasses, such as CO2, trap more of the sun’s heat on Earth caus­ing global tem­per­a­tures to rise.

Up to now, sci­en­tists dis­agreed on the cause of Ice Age glacier de­cline, with some at­tribut­ing it mainly to so­lar ra­di­a­tion and re­gional in­flu- ences such as ice sheets and ocean cur­rents.

A team of sci­en­tists led by Jeremy Shakun of Bos­ton Col­lege re-ex­am­ined the ages of more than 1,100 pre­vi­ously stud­ied gla­cial boul­ders by mea­sur­ing a par­tic­u­lar iso­tope — Beryl­lium-10 — pro­duced by ex­po­sure to cos­mic rays.

They com­pared their find­ings, the most ac­cu­rate so far, to the tim­ing of the rise of car­bon diox­ide in the at­mos­phere, data gleaned from ice bub­bles trapped in ice cores. The re­sults were un­equiv­o­cal. “The only fac­tor that ex­plains glaciers melt­ing all around the world in uni­son dur­ing the end of the Ice Age is the rise in green­house gases,” said Shakun.

Sci­en­tists are still not sure what trig­gered the grad­ual re­lease of CO2 into the at­mos­phere start­ing 19,000 years ago, or ex­actly where it came from.

“It’s fair to say that the rea­son CO2 went up and down over the Ice Ages is one of the big­gest palaeo­cli­mate mys­ter­ies out there,” Shakun said by email.

The most likely sce­nario, ac­cord­ing to co- au­thor Peter Clark of Ore­gon State Univer­sity is that huge quan­ti­ties of car­bon

bub­bled up from the sea.

50 Times Faster

“The car­bon was likely re­leased be­cause of changes in the ocean and its cir­cu­la­tion that were trig­gered by changes in the Earth’s or­bit around the sun,” he wrote in an email ex­change.

The im­pact of green­house gas emis­sions on glaciers to­day, both sci­en­tists say, is sim­i­lar to the Ice Age endgame, ex­cept that — af­ter 10,000 years of rel­a­tive sta­bil­ity — the process is hap­pen­ing 50 times faster.

“Just in the past 150 years, CO2 lev­els have surged from 280 to about 400 ppm, far higher than was re­quired to put an end to the last Ice Age,” said Shakun.

And even un­der the most op­ti­mistic sce­nar­ios for slash­ing car­bon pol­lu­tion, he added, those lev­els will in­crease by at least another 20 per­cent, though how long it will take is un­clear.

The con­se­quences of glacier loss are mul­ti­ple.

The U.N.’s cli­mate science panel says melt­ing glaciers will ac­count for a quar­ter of to­tal sea level rise, which is pegged at 26 to 98 cen­time­ters by 2100.

This is enough to swamp many small is­land na­tions and sev­eral highly pop­u­lated river deltas in Asia and Africa.

But the great­est threat is to the nearly one bil­lion peo­ple who de­pend di­rectly on glaciers — his­tor­i­cally a re­new­able re­source — for wa­ter to drink and ir­ri­gate crops.

“When you pull back and look at the pa­leo-record of car­bon diox­ide and re­al­ize that a 180 to 280 ppm rise was enough to help drive a ma­jor global melt­down, it give you pause for thought on where 400, 500 or 600 ppm leads,” said Shakun.

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