Scientists have documented five main ones mass extinction events in Earth’s history during which at least three-quarters of life has disappeared. But with humans clearing habitats, destroying species and changing the climate, are we now in a sixth mass extinction?
Many researchers argue that a sixth mass extinction is underway, with one team describing “biological destruction ” and “mutilation of the tree of life ” in their research. However, others argue that the mass extinction has not yet begun .
Robert Cowie research professor at the University of Hawaii, told Live Science that, strictly speaking, you can’t declare a mass extinction until it actually happens — after 75 percent of the species are gone.
A 2022 study led by Cowie and published in the journal Biological examinations estimates that up to 13% of known species have gone extinct since 1500 – well below the 75% mass extinction threshold.
“It hasn’t happened yet,” he said.
Some researchers have estimated that we will reach the 75% threshold within 10,000 years, while other studies have concluded that we may be at this grim milestone in just a few centuries — with the potential for an even shorter time frame if things take a turn for the worse.
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According to Museum of Natural History in London. Centuries to millennia required to reach the mass extinction threshold are well within that time frame. So if you take these estimates as estimates, researchers can claim that the event has already begun.
“We are witnessing the sixth mass extinction in real time”, Anthony Barnoski professor emeritus of integrative biology at the University of California, Berkeley, told Live Science in an email.
Studies have estimated that species are currently going extinct between 100 and 1,000 times faster than the normal background extinction rate, calculated based on when species evolved and died out in the fossil record. “I think the rate will increase as we destroy more of the planet,” Cowie said.
Barnoski noted that species extinction rates can mask rapid declines in wildlife populations because we don’t consider species extinct until the last individual is gone. Species are often declared extinct decades after they were last seen in the wild, while others continue to implement conservation measures when most of their population is dead.
“We’ve killed almost 70 percent of the wildlife on the planet since I was born,” Barnoski said. “Obviously this can’t go on much longer without making the sixth mass extinction a reality.”
And 2022 WWF report found that observed vertebrate populations of mammals, birds, amphibians, reptiles and fish declined by an average of 69% between 1970 and 2018. This figure is a global average; Latin America had the largest regional decline at 94%. Moreover, this number does not include the more numerous species of invertebrates.
Data on invertebrate declines are lacking, but some groups have suffered huge losses. For example, a 2015 study co-authored by Cowie and published in the journal Conservation Biology highlighted the decline of Amastridae snails in Hawaii due to invasive species and habitat loss. Of the 282 species that historically inhabited Hawaii, researchers can only confirm that 15 are still alive. “It’s a mass extinction,” Cowie said.
Barnoski described the destruction of biodiversity and increasing mass extinctions as “the bad news”. But he said it is not too late to save most species headed for extinction and thus prevent us from reaching the sixth mass extinction threshold.
“Even though we’re exterminating populations and species at an astonishing rate, we’re not done yet,” Barnoski said. “We still have a chance to turn things around, but the window of opportunity to do so is closing fast.”
