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Public Radio's Environmental News Magazine (follow us on Google News)

The Sixth Extinction

Air Date: Week of

This Saber-toothed tiger went extinct at the end of the Pleistocen Epoch, some 11,000 years ago. (Photo: Wikimedia Commons)

Elizabeth Kolbert’s new book, The Sixth Extinction, explores the many ways humans are helping cause the largest extinction event since an asteroid wiped out the dinosaurs. Elizabeth Kolbert discusses what's happening with host Steve Curwood.


CURWOOD: It's Living on Earth, I'm Steve Curwood. To research her book, “Field Notes from a Catastrophe”, New Yorker writer Elizabeth Kolbert traveled the world to find places where climate change is already having an impact. For her latest book, Elizabeth Kolbert again packed her bags, but with a different aim; to see how climate change, and other impacts of the human race are causing the largest mass extinction since an asteroid wiped out the dinosaurs some sixty-five million years ago. Elizabeth Kolbert says this book, The Sixth Extinction, An Unnatural History, is in many ways a sequel to her previous one.

KOLBERT: I actually went looking for a follow up, another book on climate change to do, because I thought climate change, wow, that’s such a huge story; surely I have not exhausted that story yet. And while I was looking around for that, I really came to the realization that climate change is just part of an even bigger story, which are the many ways in which people are changing the planet on a very grand geological scale that will be essentially permanent. We’re changing the world in ways that geologists in the very distant future will still be able to see that something very, very unusual happened at the moment that for us is the present.

CURWOOD: Of course, there’s a lot to talk about, but first let’s talk about a couple of the five extinctions, before this sixth one that humans are driving. It strikes me that these were all somewhat random.

KOLBERT: Yes, I think that’s a very important point to make. The worst of what are called the “big five” of the last half billion years occurred about 250 million years ago. It’s known as the end Permian extinction, and it wiped out something like 90 percent of the species on the planet. And people say, scientists who have studied it say, it came perilously close to wiping out multi-cellular life altogether and sort of pushing the planet back to the state of having only uni-cellular life.

The best hypothesis right now is that it was caused by this massive burst of volcanic activity that took place in what is now Siberia, and formed a formation known as the “Siberian Trap”, which is this huge lava flow that stretches over thousands and thousands of square miles, and that that released a lot of CO2 somehow, it’s not even clear exactly how because it doesn’t follow even from this massive burst of volcanism that that much CO2 would have been emitted, but a lot of CO2 was emitted into the atmosphere, it warmed the planet very radically and it acidified the oceans, it changed the chemistry of the oceans very radically. And one of the very sobering parallels between what we’re doing and what happened at the end of the Permian period is we are also emitting massive amounts of carbon dioxide into the atmosphere and doing it very very quickly.

CURWOOD: Now, talk to be about how you see climate change and the burning of fossil fuels as the driver of extinction for marine creatures.

KOLBERT: In the case of marine creatures, they’re being hit with at least a double whammy. I mean there are many other forces as you know affecting marine life these days. But two big effects of carbon emissions: one is climate change, which is warming oceans very very rapidly just as its warming our land masses but also what happens when you emit CO2 into the atmosphere is a lot of it gets dissolved in the oceans. It gets absorbed by the surface layer of the oceans and it dissolves in the water and when CO2 dissolves in water it forms an acid, carbonic acid. It’s a very weak acid, and you drink it when you drink Coke or club soda. But you pour enough of that into the water and it’s changing the water chemistry.

CURWOOD: Now, you went out with some researchers who are looking at the effects of carbon dissolving in the oceans.

KOLBERT: Yes, I went out with a guy named Jason Hall Spencer who had a really interesting revelation one day when he was taken to go swimming in this spot in the Bay of Naples where there are volcanic vents. So there are these vents at the bottom of the sea that are spewing what turns out to be almost pure carbon dioxide into the water and acidifying the water there - very much in the same way we are acidifying the water - and it occurred to him if he could map what lived in that area, you could sort of look forward in time. And as the chemistry changes, what’s going to happen to marine life.

And he did this very elaborate census, which required him to spend hours and hours sitting under the water counting every mollusk that was roaming by. You could see that when you were far away from the vent, several hundred yards away, you could see there were sea urchins and there were sea cucumbers and there were all sorts of seaweed and then as you got closer and closer to the vents, various things started to drop out, and then when you got right up close to the vents, it was sort of like a lunar landscape. And there were these sort of unfortunate creatures, these mollusks or limpets that had wandered in and their shells were starting to dissolve. You could see that they had these pitted shells, in some cases holes in them because the effect of the water was to actually eat away at their shells.

CURWOOD: And this is like a tenth of a decimal point change in the acidity of the ocean there.

KOLBERT: Well, so far we have affected a tenth of a decimal point change. We’ve already done that and because the Ph scale is a logarithmic scale, that represents a 30 percent increase in acidity already, so since the start of the Industrial Revolution. And if we continue on our present course, by the end of the century we will have affected basically a 0.4 change in the Ph scale, and that represents 150 percent increase in acidity.

CURWOOD: Now we know that the polar regions of the Earth are warming much more quickly that the Equatorial areas, Polar bears are a poster animal for climate disruption, but in your book you note that species in topical areas, including rainforests, are actually at more risk of extinction. Can you explain that?

KOLBERT: Yes, I mean it’s really interesting. As you pointed out the Arctic is warming very very fast, and that’s absolutely true, and if you’re a creature that’s dependent on Arctic sea ice which isn’t going to be there quite possibly in the summer within just a few decades from now, you are quite possibly a creature that’s in a lot of trouble. But the fact is that most organisms live in the tropics, the vast majority of species on Earth live in the tropics, and one of the defining characteristics of species that live in the tropics seems to be that you occupy this very narrow range of climate conditions.

So, for example, I went to the Andes with a scientist named Miles Silman, and what he had done was laid out these plots of trees where they’d literally counted every tree and identified what species they were from, and these plants ran down a ridge so that each of these plots has a different average annual temperature. And as we were walking down this mountain to look at these plots, he said to me, find a leaf on the forest floor that has an interesting shape and watch it, and you’re only going to find this leaf for a couple hundred yards because the range of this species is so narrow that you can follow it just as we walk along and let’s say an hour or half an hour. You have now gone through the entire range of this species. So these species seem to have very specific climatic conditions that they need, and as we change them, once again, what’s going to happen? Presumably some of them are going to move and he’s found that that’s the case. Some species are effectively moving up slope, but some are just sitting there. They don’t seem to have the ability to move. So we’re going to find out what’s going to happen to them.

CURWOOD: So let’s talk about some smaller extinctions for a moment. You note in your book that as early humans settled the Earth there were pulses of extinction of the large megafauna, you know, the mastodons, and the mammoths and the sabertooth tiger and all that followed them. You say that we didn’t really notice it at the time. Could you tell me the story and what it means?

KOLBERT: Sure, until relatively recently on Earth on all the different continents there had been these huge, huge animals which now on several continents, you didn’t find them anymore. You didn’t find them anymore in North America, you didn’t find them in South America, and in Australia you had these enormous marsupials, which are known colloquially as rhinoceros wombats. You didn’t find those anymore. They also in Australia had these giant tortoises that you didn’t find anymore, and what seems to be pretty clear from the evidence now is that the pattern and the timing does track when humans arrived in a continent.

CURWOOD: And so, what did we do as humans?

KOLBERT: The prevailing theory right now is that we simply hunted them. What large animals tend to share - certainly large mammals - is that they have a very low reproductive rate. So you don’t have to depress their numbers very much - you don’t have to cut into that reproductive rate very much before you start to see their numbers decline. So being very large and slow to reproduce is a really good strategy if you don’t have any predators. You’ve escaped predation, you’re so big and fierce that you don’t have any predators, but as soon as you have a predator like a human who can hunt something larger than itself, which is quite remarkable in evolutionary history, then your numbers can start to slide. And over many hundreds of years, you know it didn’t happen right away, but over hundreds of years of hunting pressure, they simply went extinct. And so as you suggested before, people didn’t realize that was happening as it was going on, but it seems pretty clear that people were responsible.

CURWOOD: By the way, in Africa, the region where modern humans evolved, we still have large animals like elephants and rhinos and big cats. Coincidence?

KOLBERT: There’s certainly a hypothesis that perhaps in Africa having co-evolved as I say, not just with modern humans, but with our early toolmaking pre-modern human ancestors, that they did evolve the appropriate defenses and so were not as vulnerable to us.

CURWOOD: Amphibians actually predate the dinosaurs, but they seem to now be the class of animals most at risk for extinction, I read in your book. Can you explain more why?

KOLBERT: What seems to be a big killer in the case of amphibians is a fungal disease that was presumably moved around the world by people somehow, because it popped up very quickly in very disparate places: in South America, in Central America, in Australia. So it seems that it must have been something that was moved around the world. And one theory which is intriguing is back in the 50s, there was a frog called an African clawed frog that was used for pregnancy tests, and many of them were exported from Africa, and what happens is if you inject an African clawed frog with the urine of a woman who’s pregnant then a female African clawed frog will lay eggs pretty quickly thereafter. So it was a pregnancy test, and those frogs were moved all around the world, and they seemed to carry this fungus, but not to be affected by it themselves. So one possibility is that that is the way this fungus was moved around the world.

CURWOOD: Now many people listening to us are, of course, very concerned about the notion of extinction. But some people will say, “Hey, extinction’s just part of nature. Why should be so worried?”

KOLBERT: Well, extinction is part of nature, once again if you’re taking the very very long view of things. But extinction at the rate that we’re seeing it is not. And it means if things are going extinct faster than new species are being created, which is evidently the case right now, it means that the variety and diversity of the Earth is shrinking.

CURWOOD: I imagine reporting this book had to be a lot of fun at times. I mean, you were in the rainforest in Peru, you got out on the Great Barrier Reef, you were all over Europe. So, along the way what signs of hope did you find?

KOLBERT: Well, I met a lot people who are incredibly dedicated to trying to save what’s left of the natural world, and that is a very hopeful thing. People are really concerned about endangered species, but we’re these very mixed creatures, you know on the one hand we do really care about the creatures with whom with we share the planet, and on the other hand, without really intending to, we are very good at changing the world in ways that make it very difficult for them.

CURWOOD: Elizabeth Kolbert’s book is called The Sixth Extinction, an Unnatural History. Thanks so much for taking the time with me today.

KOLBERT: Thanks for having me.



The Sixth Extinction


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