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201305Mar18:46

Global tip­ping point not backed by science

Infor­ma­tion
pub­lished 05 March 2013 | mod­i­fied 05 March 2013
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worldmap landuseA group of inter­na­tional eco­log­i­cal sci­en­tists led by the Uni­ver­sity of Ade­laide have rejected a doomsday-​like sce­nario of sud­den, irre­versible change to the Earth’s ecol­ogy.

In a paper avail­able online on Feb­ru­ary 27 in the jour­nal Trends in Ecol­ogy and Evo­lu­tion, the sci­en­tists from Aus­tralia, US and UK argue that global-​scale eco­log­i­cal tip­ping points are unlikely and that eco­log­i­cal change over large areas seem to fol­low a more grad­ual, smooth pat­tern.

This opposes recent efforts to define ‘plan­e­tary tip­ping points’ — crit­i­cal lev­els of bio­di­ver­sity loss or land-​use change that would have global effect — with impor­tant impli­ca­tions for sci­ence and policy-​makers.

This is good news because it says that we might avoid the doom-​and-​gloom sce­nario of abrupt, irre­versible change
Prof Barry Brook, lead author, Uni­ver­sity of Ade­laide »


“A focus on plan­e­tary tip­ping points may both dis­tract from the vast eco­log­i­cal trans­for­ma­tions that have already occurred, and lead to unjus­ti­fied fatal­ism about the cat­a­strophic effects of tip­ping points. An empha­sis on a point of no return is not par­tic­u­larly help­ful for bring­ing about the con­ser­va­tion action we need. We must con­tinue to seek to reduce our impacts on the global ecol­ogy with­out undue atten­tion on try­ing to avoid arbi­trary thresh­olds.”

A tip­ping point occurs when an ecosys­tem attribute such as species abun­dance or car­bon seques­tra­tion responds rapidly and pos­si­bly irre­versibly to a human pres­sure like land-​use change or cli­mate change. Many local and regional-​level ecosys­tems, such as lakes and grass­lands, are known to behave this way. A plan­e­tary tip­ping point, the authors sug­gest, could the­o­ret­i­cally occur if ecosys­tems across Earth respond in sim­i­lar ways to the same human pres­sures, or if there are strong con­nec­tions between con­ti­nents that allow for rapid dif­fu­sion of impacts across the planet.

“These cri­te­ria, how­ever, are very unlikely to be met in the real world,” says Pro­fes­sor Brook. “First, ecosys­tems on dif­fer­ent con­ti­nents are not strongly con­nected. Sec­ond, the responses of ecosys­tems to human pres­sures like cli­mate change or land-​use change depend on local cir­cum­stances and will there­fore dif­fer between local­i­ties.”

The sci­en­tists exam­ined four prin­ci­pal dri­vers of ter­res­trial ecosys­tem change — cli­mate change, land-​use change, habi­tat frag­men­ta­tion and bio­di­ver­sity loss — and found they were unlikely to induce global tip­ping points.

Co-​author Asso­ciate Pro­fes­sor Erle Ellis, Uni­ver­sity of Mary­land, Bal­ti­more County, says: “As much as four fifths of the bios­phere is today char­ac­terised by ecosys­tems that locally, over cen­turies and mil­len­nia, have under­gone human-​driven régime shifts of one or more kinds. Recog­nis­ing this real­ity and seek­ing appro­pri­ate con­ser­va­tion efforts at local and regional lev­els might be a more fruit­ful way for­ward for ecol­ogy and global change sci­ence.”


(Source: The Uni­ver­sity of Ade­laide media release, 28.02.2013)
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Tiger range countries map

Tiger map” (CC BY 2.5) by Sander­son et al., 2006.

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