Last week, a group of Stanford researchers published a paper with a very simple, very terrifying message. The number of species that have gone extinct over the past few centuries is high—as in, up to 100 times higher than Earth's history suggests is normal. That drastically high rate means it's logical that the next mass extinction is starting now.
And because no natural disaster—say, for example, the splitting of a continent or an asteroid crash—has brought us to the brink, the fault must be ours. And based on the accelerated rate of extinctions, the end could come in as soon as 250 years. Simple, right?
Let's back up. So far, there have been five mass extinctions in Earth's history:
1. The End-Ordovician mass extinction wiped out between 82 and 88 percent of species. (445-440 million years ago)
2. The Late Devonian mass extinction killed 79 to 87 percent of species (375-359 million years ago)
3. The End-Permian mass extinction killed 93 to 97 percent of species, and is also referred to as the Great Dying (252 million years ago)
4. The End-Triassic mass extinction killed between 76 and 84 percent of all species (201 million years ago)
5. The End-Cretaceous mass extinction wiped out between 71 and 81 percent of all species, including all non-bird dinosaurs (66 million years ago)
The idea that we're at a sixth mass extinction is not a new one. Scientists have been warning that the enormous impact humans have on the Earth and its ecology could lead to a mass extinction for years. Consider this excerpt from a CNN article published back in 2002:
"There is virtual unanimity among scientists that we have entered a period of mass extinction not seen since the age of the dinosaurs, an emerging global crisis that could have disastrous effects on our future food supplies, our search for new medicines, and on the water we drink and the air we breathe."
In a video explaining the study's finding, co-author Paul Ehrlich says that his team's findings are a reaffirmation of earlier predictions: "[Our paper] shows without any significant doubt that we are now entering the sixth great mass extinction event."
In fact, one of the differences between Ehrlich et. al's study and previous ones is that his team takes a conservative approach to the likelihood that we're about to go the way of the dinosaurs. The Stanford researchers assumed a high normal rate of extinction (called background extinction) and made a low guess as to the amount of extinctions we've seen over the past few hundred years. So their results are even more troubling.
In the paper's abstract, the authors explain their approach:
"The oft-repeated claim that Earth’s biota is entering a sixth 'mass extinction' depends on clearly demonstrating that current extinction rates are far above the 'background' rates prevailing between the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction."
Using this methodology, they found that "these estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way."
There is a silver lining, however. Humans could theoretically turn things around—The Washington Post notes that we have about one generation to get it together. But, the researchers say, we have to act fast. Based on how our leaders are reacting to pleas to fight global warming, that seems like a long shot.
Danielle Wiener-Bronner is a news reporter.