Scientists warn of sixth mass extinction threat

The biodiversity crisis is “as serious as climate change” but is not well known to the general public, laments Gerardo Ceballos, a professor at Mexico’s National Autonomous University and co-author of the study, published in the journal PNAS.

But there is “urgency” because what is at stake is “the future of humanity,” he told AFP.

There are already many studies on species extinction, but this one is unique in that it looked at the extinction of entire species.

In the classification of organisms, genus lies between the ranks of genus and family. For example, dog is a species belonging to the Canis genus in the Canidae family.

“I think this is the first time we’ve tried to assess the rate of extinction on a larger scale than species,” Robert Covey, a biologist at the University of Hawaii who was not involved in the study, told AFP. “It demonstrates the loss of entire branches of the tree of life,” the representation of life originally created by Charles Darwin.

“We’re not just cutting branches, we’re using chainsaws to remove large branches,” said Anthony Barnoski, professor emeritus at the University of California, Berkeley.

73 extinct species

The researchers relied specifically on the International Union for Conservation of Nature (IUCN) lists of endangered species. They focused on vertebrate species (except fish), and had more data.

Of about 5,400 species (comprising 34,600 species), 73 of them have gone extinct in the last 500 years — most in the last two centuries. Birds first, followed by mammals, amphibians and reptiles.

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To understand whether this rate was higher than normal, the researchers compared this result with extinction rates estimated using fossil traces over a much longer period of time.

“Given the rate of extinction in the last million years, you would expect two species to go extinct, but we lost 73,” said Gerardo Ceballos.

According to the study, the extinction of these 73 species should have taken 18,000 years, not 500.

These estimates remain uncertain, many species are not even known, and the fossil record is incomplete. But according to the researcher, they may be underestimated.

The reason for these destructions? Human activities that destroy habitats for crops, infrastructure, and other needs, but also overexploitation (overfishing, poaching, animal trafficking, etc.).

However, the loss of one species can have consequences for the functioning of an entire ecosystem. A possible “collapse of civilization” in the long run, argues Gerardo Ceballos.

“If you have a wall made of bricks, each brick is one of a kind, removing one brick will not collapse the wall,” he compares. “But if you take too many more, the wall falls.”

Five Great Mass Extinctions ©Our World in Data

“Still Time” to Act

According to him, there is no doubt that this is the sixth mass extinction. However, whether it has already started remains a matter of debate, although all experts agree that the current rate of extinction is alarming.

The last mass extinction was 66 million years ago, when an asteroid impact wiped out the dinosaurs.

“An arbitrary value of 75% of species lost in a short period of time is widely used to define a mass extinction,” explains Robert Covey. According to this threshold, the sixth mass extinction “has not yet occurred.”

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But “if species continue to die out at the current rate (or faster), this will happen,” he says. “Let’s say we’re at the beginning of a possible sixth mass extinction.”

His uniqueness? It is fueled by a race, humans, and has the power to address it.

“The window for action is closing quickly, but we still have time to save many species,” warns Gerardo Ceballos.

Stopping the destruction of natural habitats and restoring what’s been lost is a priority, insists the researcher, who hopes for faster awareness: “Governments, businesses and people need to know what’s going on. What’s going to happen, and what the consequences are.”

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