Study: 6th mass extinction already underway -- and we're the cause

Katharine Lackey | USA TODAY

Show Caption Hide Caption How humans can try to prevent 6th mass extinction Scientists are warning the planet is in the early stages of a mass extinction, but they say there is something humans can do to try to prevent it.

The Earth's sixth mass extinction is already underway — and humans are the driving force behind it, according to a new study.

"Recent extinction rates are unprecedented in human history and highly unusual in Earth's history," according to a study published Friday in the journal Science Advances. "Our global society has started to destroy species of other organisms at an accelerating rate, initiating a mass extinction episode unparalleled for 65 million years."

Researchers used "extremely conservative assumptions" to determine extinction rates that prevailed in the past five annihilation events. Still, they found the average rate of vertebrate species lost over the past century was up to 114 times higher than normal.

For example, about 477 vertebrate species have gone extinct since 1900, according to the study. Based on previous extinctions, only nine species would have been expected to die off in the same time frame had it not been for mankind's involvement.

"The number of species that have gone extinct in the last century would have taken ... between 800 and 10,000 years to disappear," the study reported. "These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already underway."

The previous five mass extinctions happened well before mankind walked the Earth, and are believed to have been mainly caused by natural disasters, such as asteroid impacts and volcanic eruptions.

The last mass extinction happened some 65 million years ago, killing off the dinosaurs. Overall, each mass extinction event has rid the planet of up to 96% of its species each time.

In the past few decades, several animal species have been labeled extinct, including the Chinese paddlefish, Yangtze River dolphin, Pyrenean ibex and western black rhinoceros.

Earlier this week, the U.S. Fish and Wildlife Service announced it would push for the extinct eastern cougar to be removed from the endangered species list. The big cat likely vanished about 70 years ago, the agency said in a statement. Its disappearance is largely linked to over-hunting and loss of habitat from European immigrants dating to the 1800s.

Among the World Wildlife Fund's critically endangered species — those at the most at risk of going extinct today — are the Amur leopard, black rhino, leatherback turtle, Sumatran tiger, and western lowland gorilla.

In as little as three generations, the current extinction pace could dramatically alter the number of species on the planet — permanently, the study said. In previous extinction events it took hundreds of thousands to millions of years for the planet to rediversify.

Researchers said it's not too late to avoid a true sixth mass extinction, but it will "require rapid, greatly intensified efforts to conserve already threatened species and to alleviate pressures on their populations — notably habitat loss, overexploitation for economic gain and climate change."

"However, the window of opportunity is rapidly closing."