Study identifies 6th mass extinction event, lists human activity as primary cause

Ariel Hayat/Senior Staff
The Steller's sea cow went extinct only 27 years after being discovered in the North Pacific in 1741. It acts as an example of modern species extinction caused by human-related activities.

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After years of warnings from ecologists about the dangers of biodiversity loss, a new study has quantified an ongoing mass extinction event — the sixth in our planet’s history — and suggests humans are largely to blame.

The paper, published June 19 in the journal Science Advances, takes a “conservative” approach to measuring the extent of the situation because previous estimates have been criticized for overestimating the severity of the extinction crisis.

The primary researchers — from institutions such as UC Berkeley, Stanford University and the National Autonomous University of Mexico — compared current extinction rates with a normal baseline rate of two mammal extinctions per 10,000 vertebrate species per 100 years. Based on this measure, about nine vertebrate species should have disappeared from the earth since 1900. But the paper’s “conservative” extinction count stands at 477, which should have taken as many as 10,000 years to occur.

Paul Ehrlich, senior fellow at the Stanford Woods Institute for the Environment and co-author of the study, notes that the species extinction rate is the highest it has been in 65 million years.

“We’re essentially doing to the planet what the meteor did that took care of the dinosaurs,” he said of the data’s implications.

Seth Finnegan, an assistant professor in UC Berkeley’s integrative biology department who specializes in mass extinction, said the researchers’ study contrasts with other studies that tend to estimate modern extinction rates indirectly. For example, some measure areas of destroyed habitats and then extrapolate extinction predictions based on how many species are believed to exist in those areas.

“This study doesn’t take the inferential approach,” he said. “They are tallying up well-documented, well-observed extinctions of mammals.”

Though extinction can occur because of a variety of environmental factors, the study emphasizes humans’ effect on the alarming rate of species loss. According to Finnegan, industrialization has “drastically accelerated humans’ impact on Earth’s ecosystems.”

Co-author Anthony Barnosky, a campus professor of integrative biology, cited a high per-capita use of fossil fuels and the over-exploitation of ecosystems for economic gain as major contributing factors.


“In one or two human lifetimes, we are the ones wiping out what evolution took millions of years to create,” he said.

In addition to being the driving force behind the sixth mass extinction, humans will ultimately face “high moral and aesthetic costs” in as little as three lifetimes, according to Barnosky. Crucial ecosystem services, such as crop pollination and water purification, will suffer if high rates of extinction persist, the study says.

Considering that it took up to millions of years for the planet to rediversify after the previously recorded mass extinctions, the study says, these consequences would be effectively permanent on human time scales.

Ehrlich said that some conservation efforts could potentially slow the process of mass extinction but said he agrees with the study’s conclusion that “the window of opportunity is rapidly closing.”

“Conservation biologists are hard at work trying to stop it,” he said. “But there’s not a hope of changing this in the long run if human populations keep increasing and we maintain a pattern of perpetual growth on a finite planet.”

Contact Ariel Hayat at [email protected] and follow her on Twitter @ArielHayat.