Mark Car­war­dine

All you need to know about the sixth ex­tinc­tion

BBC Wildlife Magazine - - Contents - Mark Car­war­dine’s

WHAT IS THE SIXTH EX­TINC­TION?

Over the last half a bil­lion years, life on Earth has been nearly wiped out five times. These mass ex­tinc­tions were caused by cli­mate change, vol­canic erup­tions and, 65m years ago, a gi­ant as­ter­oid smash­ing into the planet. Many ex­perts be­lieve that the an­ni­hi­la­tion of wildlife we are wit­ness­ing to­day means that we are in the mid­dle of a sixth mass ex­tinc­tion. What makes this one dif­fer­ent is that we are to blame.

DOES EV­ERY­ONE AGREE?

No. Some sci­en­tists ar­gue that we are not yet in the throes of a sixth mass ex­tinc­tion, though even most doubters agree that we are on the brink. What is be­yond dis­pute is that we are liv­ing in a time of very el­e­vated ex­tinc­tion rates. The great fear is that mass ex­tinc­tions are be­lieved to un­fold grad­u­ally, and then sud­denly. So we’ll bump along where every­thing seems mod­er­ately okay and then, sud­denly, we’ll be past the tip­ping point.

ISN’T EX­TINC­TION NAT­U­RAL?

Yes. Some 99.9 per cent of all species that have ever lived are now ex­tinct. First, there is ‘back­ground ex­tinc­tion’ – the tick, tick, tick of species grad­u­ally dis­ap­pear­ing through nat­u­ral se­lec­tion be­cause they suc­cumb to com­pe­ti­tion, as Dar­win pre­dicted in his the­ory of evo­lu­tion. Sec­ond, there are mass ex­tinc­tions – pe­ri­ods in the Earth’s his­tory when Jan­uary 2018 a sig­nif­i­cant pro­por­tion of species are wiped out – when luck, not com­pet­i­tive in­fe­ri­or­ity or su­pe­ri­or­ity, plays a fun­da­men­tal role in de­ter­min­ing which species sur­vive and which don’t.

SO WHAT’S CAUS­ING THE SIXTH MASS EX­TINC­TION?

Quite sim­ply, hu­man over­pop­u­la­tion and over-con­sump­tion. There were 2.5 bil­lion peo­ple on the planet in 1950, there are 7.6 bil­lion to­day, and there are ex­pected to be more than 9 bil­lion by 2050. The more peo­ple, the greater the pres­sure from habi­tat de­struc­tion, di­rect ex­ploita­tion, pol­lu­tion, the spread of alien species and global warm­ing.

HOW MANY SPECIES ARE WE LOS­ING?

Es­ti­mates vary widely. The Mil­len­nium Ecosys­tem Assess­ment, which in­volved 1,360 ex­perts world­wide, es­ti­mated an ex­tinc­tion rate of 24 species a day. Sci­en­tists at the UN Con­ven­tion on Bi­o­log­i­cal Di­ver­sity re­cently con­cluded that the fig­ure should be 150 per day. Other es­ti­mates are much higher – be­tween 1,000 and 10,000 times the ‘nat­u­ral’ ex­tinc­tion rate (which is be­lieved to be roughly two out of ev­ery mil­lion species dis­ap­pear­ing per year – so slow that spe­ci­a­tion and ex­tinc­tion more or less equal out). How­ever, there is gen­eral agree­ment that ex­tinc­tion rates have reached lev­els un­par­al­leled since the di­nosaurs died out 65 mil­lion years ago – with no sign of a slow­ing down.

WHY DOES IT MAT­TER?

A study pub­lished in July 2017 in Pro­ceed­ings of the Na­tional Acad­emy of Sciences es­ti­mates that – shock­ingly – we have lost more than half of all in­di­vid­ual an­i­mals since 1970. The sci­en­tists found that more than a bil­lion pop­u­la­tions of mam­mals, birds, rep­tiles and am­phib­ians have been lost all over the planet. It’s not just about los­ing en­dan­gered species – we are swing­ing a wreck­ing ball through the Earth’s bio­sphere.

WILL WE BE AMONG THE SUR­VIVORS?

When a mass ex­tinc­tion oc­curs, it takes mil­lions or tens of mil­lions of years for life to re­cover and, when it does, it gen­er­ally has a new cast of char­ac­ters. Hu­mans are very adapt­able, but no one knows if we might be among them. Even if we can sur­vive, what sort of world would we be liv­ing in? And – this is the big ques­tion – do we re­ally want to keep go­ing down the same tra­jec­tory to find out?

WE ARE IN THE MID­DLE OF A SIXTH MASS EX­TINC­TION. WHAT MAKES THIS ONE DIF­FER­ENT IS THAT WE ARE TO BLAME.”

An as­ter­oid caused the ex­tinc­tion of the di­nosaurs 65m years ago.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.