CAR­BON DAT­ING

An im­por­tant new book con­sid­ers the long-term im­pli­ca­tions of our re­la­tion­ship with car­bon diox­ide, writes Tim Flan­nery

The Weekend Australian - Review - - Books -

EAR­LIER this year, the mem­bers of the Royal Ge­o­log­i­cal So­ci­ety met in Lon­don to con­sider whether a new divi­sion of the ge­o­log­i­cal time scale should be recog­nised. Such di­vi­sions mark pe­ri­ods of pro­found plan­e­tary change, such as the Cam­brian ex­plo­sion and the ex­tinc­tion of the di­nosaurs.

The pro­posed new divi­sion, known as the An­thro­pocene, will mark the mo­ment when hu­mans be­gan to ex­ert per­va­sive in­flu­ence on the earth. Reach­ing a de­ci­sion may take years, but if the pro­posal is ac­cepted, the be­gin­ning of the An­thro­pocene will be sig­ni­fied by a ‘‘ golden spike’’, driven into the rocks that mark the pe­riod’s dawn.

But where should the golden spike be placed? In rocks tens of thou­sands of years old, dat­ing to when hu­mans be­gan ex­ter­mi­nat­ing the me­gafauna? Or in sed­i­ments dat­ing to 1945, when the dawn of the atomic age left its in­deli­ble mark on the planet? Wher­ever its cho­sen start­ing point, it’s in­dis­putable that hu­mans have long ex­erted con­sid­er­able in­flu­ence on the earth.

Given our ever-more ca­pa­ble tech­nol­ogy, it seems that our ac­tions so far are just the be­gin­ning. Yet as Amer­i­can ecol­o­gist and pa­le­o­cli­ma­tol­o­gist Curt Stager points out in Deep Fu­ture, al­ready these are suf­fi­cient to in­flu­ence the earth for thou­sands of years to come.

Stager be­gins this ex­tra­or­di­nary book by tack­ling a mis­con­cep­tion of the sci­en­tists’ own mak­ing. The pro­jec­tions of the In­ter­gov­ern­men­tal Panel on Cli­mate Change gen­er­ally only ex­tend to 2100, which in Stager’s view mis­leads many to imag­ine that the in­flu­ence of the hu­man-pro­duced green­house gases will some­how cease at that point. The re­al­ity, he tells us, is that ‘‘ shock­ingly long-term cli­matic changes await us as a re­sult of mod­ern hu­man ac­tiv­ity’’.

Just how long term is spelled out by the work of David Archer, an oceanog­ra­pher who has de­vel­oped com­puter mod­els that run for­ward in time for hun­dreds of thou­sands of years. Ac­cord­ing to one of Archer’s col­leagues, quoted by Stager, the rea­son that ef­fects will be so long-lived is: ‘‘ Our car­bon emis­sions won’t be gone nearly as quickly as we once thought. In fact, they’ll stick around pretty much for­ever.’’

The pre­cise longevity and im­pact of the car­bon pol­lu­tion be­ing pro­duced this cen­tury de­pends on how much we emit. The IPCC has mod­elled a low-growth emis­sions sce­nario known as B1. It en­vis­ages that hu­mans will act ag­gres­sively to limit car­bon pol­lu­tion, so that the con­cen­tra­tion of CO in the at­mos­phere re­mains be­low 600 parts per mil­lion (up from 391 parts per mil­lion to­day). If such a course is fol­lowed, global emis­sions must peak in the next cou­ple of decades.

As Stager

de­tails,

Archer and

his

col- leagues es­ti­mate that if this oc­curs tem­per­a­tures will peak in 200 to 300 years, at 2C to 4C higher than present, and sea lev­els will stop ris­ing sev­eral cen­turies to sev­eral mil­len­nia from now, hav­ing peaked at 6m to 7m above present lev­els.

But the big sur­prise is what hap­pens to the CO . Be­cause the oceans and land have a fi­nite ca­pac­ity to ab­sorb CO , about onequar­ter of what we have emit­ted by 2100 ‘‘ lasts es­sen­tially for­ever’’. In­deed, even 50,000 years from now, that resid­ual car­bon pol­lu­tion will be acting to keep earth’s tem­per­a­ture above its pre-in­dus­trial level.

The con­se­quences of a busi­ness-as-usual ap­proach would see at least five times more car­bon pol­lu­tion reach­ing the at­mos­phere. In this sce­nario, emis­sions would not peak for more than a cen­tury and at­mo­spheric con­cen­tra­tions of CO would peak at 2000 parts per mil­lion three cen­turies from now. As a re­sult, the en­tire ocean would be acid­i­fied, be­com­ing ‘‘ a cor­ro­sive sol­vent to shell-bear­ing sea-crea­tures’’, and tem­per­a­tures would not peak for about a 1000 years, hav­ing reached 5C to 9C higher than to­day.

But again the as­ton­ish­ing thing is the longevity of the im­pact, with full re­cov­ery tak­ing a half-mil­lion years. Such long-term ef­fects would com­pletely dis­rupt the nat­u­ral cy­cle of ice ages that have char­ac­terised earth for the past sev­eral mil­lion years, with no new ice age oc­cur­ring for hun­dreds of thou­sands of years.

De­spite the long-term ef­fects that Stager sees from our present pol­lu­tion, he’s no catas­trophist. Fu­ture rises in sea level are be­lieved by some, such as cli­mate sci­en­tist James Hansen, to be pro­foundly dis­rup­tive. Stager finds no ev­i­dence in the fos­sil record

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