New report suggests Earth on the brink of a great extinction

HARI SREENIVASAN: Plant and animal extinctions are happening at a rate 1000 times greater than before humans walked the Earth. This according to new research published in the journal Science this week. The planet has been through five major extinctions before, and scientists now think we are on the cusp of a sixth. Earlier I spoke with lead researcher Stuart Pimm of Duke University.

STUART PIMM: Sixty million years ago an enormous asteroid plowed into the Yucatan peninsula of Mexico. I wouldn't want to be here in Miami when that happened. It sterilized much of North America and eliminated the dinosaurs. That kind of catastrophe will be what will happen over the next 100 years if we don't do something about the species extinction crisis. We will leave to our children and our grandchildren a much depleted planet.

HARI SREENIVASAN: So how do we know about the rate of extinction since humans have only been on the planet for a certain period of time>

STUART PIMM: Well, there's two parts to this. One of them is what's happening now or at least what's happened for the last 50 to 100 years. We can follow species from when we first learned about them to the present and see what fraction of them are dying off. And they're dying off at a pretty hefty rate. Working out what happened before humans came along is a little more difficult. But the fossil record can tell us a lot about that. We also learn a lot from their DNA, from the molecular evidence of how species are born and how fast they die off. And it's comparing those two things – what's happening to species now with what happened in the geological past that allowed us to come up with this statement of how fast species are going extinct.

HARI SREENIVASAN: So help us put this startling extinction number in perspective a bit.

STUART PIMM: Extinction is a death rate. We're used to think of human beings as dying off at a rate of one or two people a year. Species ought to die off at the rate of one species in 10 million every year. What's happening is that species are going extinct at a rate of 100 to a 1,000 species extinctions per million species. That's a rate that's very very much higher that we thought it was.

HARI SREENIVASAN: And what's causing these extinctions? Is it humans? Is it climate?

STUART PIMM: We are the ultimate problem. There are seven billion people on the planet. We tend to destroy critical habitats where species live. We tend to be warming the planet. We tend to be very careless about moving species around the planet to places where they don't belong and where they can be pests.

HARI SREENIVASAN: One of the things you mentioned in your paper is that people are assisting in conservation efforts with technology already in their hands today.

STUART PIMM: Absolutely. There are millions of people around the world who are passionate about orchids, about frogs, about birds, about dragonflies. And that crowd-sourcing is giving us an enormous source of detailed information about where species are and we can use that detailed information to set very precise, very crisp conservation priorities. It helps us know where we need to act, where we need to invest our scarce conservation dollars.

HARI SREENIVASAN: Stuart Pimm of Duke University, thanks so much.

STUART PIMM: Thanks so much for having me on the program.