Study confirms sixth mass extinction is currently underway, caused by humans

Since 1500, Earth may have lost about a tenth of its 2 million known species, say scientists

Vishwam Sankaran
Monday 17 January 2022 08:27 GMT
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Louise Thomas

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The sixth mass extinction of the planet’s biodiversity is currently underway, according to a new study confirming previous warnings that the Earth’s species have been dying off at an accelerated rate in the last few centuries.

The planet has so far undergone five major species die-offs – extinction events marked by mass biodiversity loss due to extreme natural phenomena. But the current one is entirely caused by human activities, said the study published last week in the journal Biological Reviews.

The research estimated that since the year 1500, Earth could already have lost between 7.5 per cent and 13 per cent of its 2 million known species.

“Drastically increased rates of species extinctions and declining abundances of many animal and plant populations are well documented, yet some deny that these phenomena amount to mass extinction,” Robert Cowie, lead author of the study from the University of Hawaii at Manoa, said in a statement.

Similar to climate denial, many still do not accept that the ongoing species die-offs amount to a sixth mass extinction, experts said. They added that this denial was due to a biased view of the unfolding crisis that focuses only on mammals and birds, ignoring the die-off rate of invertebrates, which constitute about 95 per cent of known animal species.

“Often, they use the International Union for Conservation of Nature’s (IUCN) Red List to support their stance, arguing that the rate of species loss does not differ from the background rate,” the researchers wrote in the study. “However, the Red List is heavily biased: almost all birds and mammals but only a minute fraction of invertebrates have been evaluated against conservation criteria.”

With invertebrates, such as insect species, being less likely to be assessed than better-known species in other groups, researchers said these creatures may well be the “most likely to be threatened” and therefore to have gone extinct.

“Thus the numbers assessed as Extinct on the Red List are under-estimates, and inappropriate to use to estimate true levels of extinction,” they wrote.

While the Red List suggests that about 900 species are extinct, researchers said the true number of die-offs vastly exceeds the normal background rate of extinctions on the planet. They estimated that between 150,000 to 260,000 of the nearly 2 million known species may already have gone extinct since around the year 1500.

Among the life forms on Earth undergoing extinction, the study found more evidence that land species, particularly island species, are suffering far greater die-off rates than continental ones.

While some said this mass extinction is a natural trajectory and that humans are just another species playing their role on Earth, researchers argued that humans are the only species that have a conscious choice regarding the planet’s future.

They called on scientists to collect and document as many species as possible before it is too late to study them.

“Denying the crisis, accepting it and doing nothing about it, or embracing it and manipulating it for the fickle benefit of people, defined no doubt by politicians and business interests, is an abrogation of moral responsibility,” the researchers added.

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