Focus-Science and Technology - - Environment -

LL AROUND THE world, mankind is hack­ing enor­mous branches off the tree of life. Since the last ice age – which ended about 10,000 years ago – the ex­tinc­tion rates of plant, mam­mal, bird, in­sect, am­phib­ian and rep­tile species have sky­rock­eted, with one es­ti­mate putting the cur­rent rate of loss at up to 140,000 species per year. That’s a prob­lem – not just for the species that are dy­ing out but for hu­mans, too. We de­pend on our com­pan­ions for food se­cu­rity, clean wa­ter, cloth­ing and even the air we breathe (see p46) .

In 2009, the Stockholm Re­silience Cen­tre listed bio­di­ver­sity loss as one of nine ‘plan­e­tary bound­aries’ that can­not be crossed with­out the world suf­fer­ing ir­re­versible en­vi­ron­men­tal change (other bound­aries in­clude ozone de­ple­tion, cli­mate change and ocean acid­i­fi­ca­tion). With­out Earth’s bio­di­ver­sity, hu­mans wouldn’t be here at all. And even the most con­ser­va­tive es­ti­mates of species loss show cause for alarm. The lat­est cal­cu­la­tions come from a group of bi­ol­o­gists led by Stan­ford Univer­sity’s Paul Ehrlich and Ger­ardo Ce­bal­los from the Na­tional Au­ton­o­mous Univer­sity of Mex­ico, who have pub­lished re­sults show­ing that Earth is ex­pe­ri­enc­ing the beginnings of an ex­tinc­tion event at least as large as the one the killed the di­nosaurs, and per­haps as big as the other four ma­jor ex­tinc­tions in our planet’s history (see be­low). “We’re not there yet but we can eas­ily get there in a cen­tury,” Ehrlich says.

Their pa­per sets out a best- case sce­nario – one that only counts species as go­ing ex­tinct if we’ve seen them go ex­tinct, and where the ‘nor­mal’

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