It's official: the planet is entering a "sixth great extinction" that even the most conservative estimates show is killing off species at rates far higher than the previous five mass die-offs—and humanity is both at fault...and at risk.

A joint study by scientists from several North American universities published last week in Science found that the rate of extinction for species in the 20th century was up to 100 times higher than it would have been without impacts of human activity, such as climate change, deforestation, and pollution.

Moreover, if those rates are allowed to continue, "life would take many millions of years to recover, and our species itself would likely disappear early on," said lead author Gerardo Ceballos of the Universidad Autónoma de México.

"[The study] shows without any significant doubt that we are now entering the sixth great mass extinction event," said co-author, Paul Ehrlich, the Bing professor of population studies in biology and a senior fellow at the Stanford Woods Institute for the Environment. "There are examples of species all over the world that are essentially the walking dead."

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Scientists have long agreed that extinction rates have reached unparalleled levels since the last mass extinction, when the dinosaurs were killed off 65 million years ago, likely by a meteor crashing into Earth. For years, conservation groups have warned of increasing extinction risks faced by mammals, birds, and amphibians, which Harvard University ecologist Edward O. Wilson in 2010 called "the backbone of biodiversity."

But Friday's study shows "even with extremely conservative estimates, species are disappearing up to about 100 times faster than the normal rate between mass extinctions, known as the background rate."

The Stanford Report elaborated:

Focusing on vertebrates, the group for which the most reliable modern and fossil data exist, the researchers asked whether even the lowest estimates of the difference between background and contemporary extinction rates still justify the conclusion that people are precipitating "a global spasm of biodiversity loss." The answer: a definitive yes. ...As species disappear, so do crucial ecosystem services such as honeybees' crop pollination and wetlands' water purification. At the current rate of species loss, people will lose many biodiversity benefits within three generations, the study's authors write. "We are sawing off the limb that we are sitting on," Ehrlich said.

"We were very surprised to see how bad it is," Ceballos told the Guardian on Friday. "This is very depressing because we used the most conservative rates, and even then they are much higher than the normal extinction rate, really indicating we are having a massive loss of the species."

"It's really signalling we’ve entered a sixth extinction and it's driven by man," Ceballos said.

Avoiding a "true" sixth mass extinction, the researchers concluded, "will require rapid, greatly intensified efforts to conserve already threatened species, and to alleviate pressures on their populations—notably habitat loss, over-exploitation for economic gain and climate change. All of these are related to human population size and growth, which increases consumption (especially among the rich), and economic inequity."

There is still time to take fast action to conserve species, ecosystems, and populations—but that window is rapidly closing, the researchers warned.