The Last Word

BBC Earth (Asia) - - Contents -

Robert Matthews on why nat­u­ral dis­as­ters don’t worry us more


hat would you think if a nu­clear-tipped mis­sile zoomed through space and nearly hit a satel­lite or two? That’s pretty close to what ac­tu­ally hap­pened on 12 Oc­to­ber last year – ex­cept that the ‘mis­sile’ was un­der no one’s con­trol.

Trav­el­ling at over 25,000 km/h, the hous­e­sized chunk of rock known as as­ter­oid 2012 TC4 packed the punch of a few dozen atomic bombs as it flew over­head, at a sim­i­lar al­ti­tude to many com­mu­ni­ca­tions satel­lites. Yet af­ter a bit of me­dia cov­er­age, the event soon went the way of all such ‘cos­mic close shave’ sto­ries, and dis­ap­peared off the news radar en­tirely.

Even when one of th­ese ob­jects ac­tu­ally does make it through the at­mos­phere – as one did over Chelyabinsk, Rus­sia in 2013, in­jur­ing over 1,000 peo­ple – we all soon for­get about it. But are we be­ing too com­pla­cent? Many scientists ar­gue that we are, and they claim to have ev­i­dence to prove it.

The trou­ble is, that ev­i­dence isn’t very com­pelling. Ex­hibit A is that the chances of dy­ing in an as­ter­oid im­pact that trashes the planet are around one in 75,000 – that’s dou­ble the risk of be­ing killed by light­ning. But wait, that can’t be right, surely? Af­ter all, the last time the Earth got to­talled was around 65 mil­lion years ago, when the di­nosaurs were wiped out.

The ex­pla­na­tion lies in the fact that this risk de­pends on more than just how fre­quent the event is. While mas­sive as­ter­oid im­pacts are far rarer than light­ning strikes, the likely death toll is mil­lions of times higher – lead­ing to that sur­pris­ingly high fi­nal risk fig­ure.

Mul­ti­ply­ing the fre­quency of the event by its con­se­quences has long been deemed the only sci­en­tific way to make de­ci­sions about risk – and the the­ory be­hind this is pretty solid. But as a way of get­ting peo­ple –and politi­cians – to take risks of nat­u­ral dis­as­ters se­ri­ously, it doesn’t re­ally work.

That’s be­cause the formula is only re­ally help­ful for de­cid­ing how best to pro­tect the whole of


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