Earth Heading for Another Mass Extinction, Scientists Warn

Last year, a U.S. government study found that amphibians in the U.S. are dying off so quickly that they could disappear from half of their habitats within the next two decades Guillermo Granja/Reuters

Five times in the history of the Earth, mass extinction events have wiped out the vast majority of life. Now it appears to be happening again.

A study published Friday in the journal Science found that plant and animal species are now going extinct at least 1,000 times faster than they did prior to humanity's arrival. That means that species are disappearing 10 times more rapidly than biologists believed before this study.

"We are on the verge of the sixth extinction," Stuart Pimm, a Duke University conservation ecologist and a lead author of the study, told the Associated Press. "Whether we avoid it or not will depend on our actions."

The study found that for every million species, between 100 and 1,000 species are dying out, mostly due to human-caused habitat destruction and climate change. According to Pimm and his team, the pre-human death rate was around .1 species lost per million per year—not one per million as researchers previously thought.

This study follows numerous recent reports that document the rapid loss of whole groups of plants and animals. Last year, a U.S. government study found that amphibians in the U.S. are dying off so quickly that they could disappear from half of their habitats within the next two decades. Warming oceans and acidification mean coral reefs may face extinction within the century, and in 2006, a study concluded that saltwater fish will be entirely extinct by 2048.

In a new book, The Sixth Extinction, New Yorker writer Elizabeth Kolbert dives deep into the stories behind several of the sudden mass die-offs in the Earth's history, and the new era of extinction and radical environmental change, referred to by many scientists as the Anthropocene, that we appear to be living in now.

The term anthropocene presents the idea that 5,000 years of human activity has so drastically altered the planet that humanity in itself is the defining environmental influence of our time. The term, according to Kolbert, was first put into scientific use by Dutch chemist Paul Crutzen, who won a Nobel Prize in 1995 for discovering what chemicals caused a hole to open in the ozone layer. Officially, at least, we have been living in the Holocene geologic period for the past approximately 12,000 years. But in a short essay, "Geology of Mankind," Crutzen argued that humans have so altered the geology of the planet so as to usher in an entirely new geological epoch.

One of the scientists on Crutzen's Nobel-winning team came home from his lab one night in the midst of studying the ozone, Kolbert writes, and told his wife, "The work is going well, but it looks like it might be the end of the world."

The idea that the natural world as we know it may be quickly slipping away is the heart of the recent studies documenting rapid species decline. The concentration of carbon dioxide in the atmosphere is the highest it has been in at least 800,000 years, and the ocean, which absorbs vast amounts of that gas, is acidifying at an alarming rate. According to Kolbert's research, if human activity continues in a business as usual manner, the oceans will be 150 percent more acidic than they were in 1800, and the ecosystems that make up the base of the marine food chain will crash.

But carbon dioxide emissions aren't the only human input driving the apparent sixth extinction: the unprecedented transport of organisms between continents are introducing nonnative fungi, disease, and invasive species to every corner of the globe. Habitat loss, identified by Pimm's study and the No. 1 driver of species extinction, will only accelerate as the climate warms and hospitable areas become inhospitable to their specific inhabitants, and as development continues to fragment previously whole habitats like forests and plains.

Kolbert ends her book on a somber note, observing that the uniquely human capacity to change the world "is also the capacity to destroy it."

And that destructive capacity, she writes, "is probably indistinguishable from the qualities that made us human to begin with."