20 Apr 12

Summary

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More or Less – April 20, 2012

Episode Theme:
How Many Species Are Going Extinct? – Debunking Global Extinction Statistics

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Overview

In this nine-minute episode of "More or Less," host Tim Harford investigates the accuracy of alarming extinction statistics often used in environmental debates. Joined by experts including Professor Georgina Mace and Professor Stephen Hubbell, the program unpacks how these numbers are calculated, questions widely-quoted extinction rates, and highlights the difficulties in accurately measuring species loss. Listeners are left with both a sense of the seriousness of biodiversity loss and the complexity and uncertainty in quantifying it.

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Key Discussion Points & Insights

1. Background: The Convention on Biological Diversity

• Tim introduces the context by referencing the 1992 Earth Summit in Rio, which launched the Convention on Biological Diversity, aiming to preserve the planet's variety of life.
• He notes that although famous extinctions (e.g., dodo, Falkland Islands wolf, golden toad) occurred before the Convention, recent cases include creatures like the Pyrenean ibex and the Baiji river dolphin.
• (00:12–01:30)

2. Defining the Problem: How Many Species Are Disappearing?

• Braulio Dias (Executive Secretary, Convention on Biological Diversity) stresses that extinction rates have recently increased due to drivers like habitat loss, pollution, and unsustainable human consumption.

• The podcast highlights the striking claim often cited by the Convention:

  “Every hour three species disappear and every day up to 150 species are lost.”
  — Ahmed Joghlav, Special Advisor, CBD (02:15)

• The credibility of these numbers is immediately questioned:

  “Doesn't that suggest there are 50 hours a day?”
  — Georgina Mace (02:26)

• Tim Harford requests more rigorous estimates, revealing deep uncertainty.

• (01:28–02:40)

3. The Challenge of Measuring Species Loss

• Uncertainty in Species Count:

  • Braulio Dias admits the total number of Earth's species is unclear—estimates range from 2 million to as high as 100 million.

    “We even don't have a good estimate to an order of magnitude of precision.”
    — Braulio Dias (02:40)

• Unknown Extinctions:

  • Professor Georgina Mace explains that of an estimate of 7–10 million species, less than 2 million are formally described; most species disappear before we even know them.

    “Of those [species], we've described less than 2 million. So the rest we don't know what they are.”
    — Georgina Mace (03:16)

• Conclusions drawn from known extinctions are therefore severely limited.

• (02:40–03:37)

4. Methods for Estimating Extinction Rates

• Counting Confirmed Extinctions:
  • The IUCN’s “Red List” identifies 801 species conclusively labeled extinct since 1500—primarily larger animals and a few plants.
  • This is far fewer than the widely quoted “150 per day.”

    “801 extinct species since the year 1500.”
    — Georgina Mace (04:15)

• Mathematical Modelling:
  • Because of data gaps, models are used to extrapolate how many species are likely lost with shrinking habitat.
  • The “species-area relationship” is the basis for these estimates: the larger the area, the more species; reduce the area, fewer species.

    "The larger the area, the greater the number of species are said to be in it... you can calculate using the model how many species must be being lost..."
    — Tim Harford (04:47)

• (03:37–05:18)

5. Controversy: Are the Models Flawed and Overstating Extinction?

• Professor Stephen Hubbell’s Critique:

  • Hubbell argues the species-area model overestimates extinction rates—possibly by a factor of two—because it ignores the spatial range needed to wipe out a species entirely.

  “People have been using a method that we show is biased and... it overestimates the extinction rate.”
  — Stephen Hubbell (05:41)

  • Explanation: Discovering a species requires less area than fully eliminating it (i.e., individuals can persist in habitat fragments longer than models suggest).
  • “If you correct the mistake in the model, it shows about half as many species are going extinct.”
    — Georgina Mace (06:28)

• Debate among Scientists:

  • Hubbell notes he and colleagues faced pressure not to publish these findings for fear of undermining conservation urgency.

    “Scientists... are obligated to notify everyone we've made a mistake and need to fix things... we were warned... not to publish our paper, but that's not advice that I felt I was morally able to take.”
    — Stephen Hubbell (08:30)

• (05:18–08:57)

6. Species That Have Actually Gone Extinct and Focusing Beyond the “Charismatic”

• Most extinctions are among less conspicuous species, not just charismatic animals.
• Even senior biodiversity officials struggle to name recent, confirmed extinctions:
  • Example: Spix’s macaw went extinct in the wild in Brazil, survives only in captivity.

  “...the population went extinct in nature. Fortunately, there are still a few individuals kept in captivity...”
  — Braulio Dias (07:27)

• (06:54–07:55)

7. Key Takeaways

• No one can safely or accurately quantify the current true extinction rate.
• The oft-quoted statistic—“every day, up to 150 species are lost”—is not scientifically substantiated.
• While exact numbers may be in dispute, experts unanimously agree species loss is a real and significant problem.
• (07:55–end)

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Notable Quotes & Memorable Moments

• Tim Harford:

  “Pandas aren't extinct.”
  — Tim Harford & Georgina Mace joke about panda survival, highlighting the public focus on charismatic species (01:12).

• On Incomplete Knowledge:

  “We even don't have a good estimate to an order of magnitude of precision.”
  — Braulio Dias (02:40)

• On The Limits of Lists:

  “No, 801 extinct species since the year 1500. Mostly animals, a few plants. But remember, this list comes from the subset of known species...”
  — Georgina Mace (04:22)

• On Mathematical Modelling Issues:

  “If you correct the mistake in the model, it shows about half as many species are going extinct.”
  — Georgina Mace, referring to Hubbell’s research (06:28)

• On Scientific Responsibility:

  “Scientists... are obligated to notify everyone we've made a mistake and need to fix things.”
  — Stephen Hubbell (08:30)

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Timestamps for Important Segments

• 00:12 – Introduction and context of biodiversity convention
• 01:28 – Are species extinctions accelerating?
• 02:15 – The “150 a day” extinction claim
• 02:40 – How many species ARE there?
• 03:47 – IUCN’s confirmed extinction numbers
• 04:47 – How models estimate extinctions
• 05:27 – Hubbell critiques the models
• 06:54 – Focusing on more than charismatic species
• 08:30 – Scientific duty to correct flawed models
• 08:57 – Final takeaways and closing remarks

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Conclusion

The episode challenges popular claims about the scale of global extinction, revealing how much remains unknown. While the actual rate of species loss is debated and probably overstated by conventional models, there is agreement: biodiversity is in decline and urgently needs attention, albeit informed by honest and accurate science.

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Transcript

[BBC Announcer]

Thank you for downloading from the BBC. For details of our complete range of podcasts and our terms of use, go to bbcworldservice.com podcasts this is more or

[Tim Harford]

less the statistical spine of the otherwise floppy media. This nine minute episode focuses on global species extinction rates and was broadcast on the BBC World Service. Hello and welcome to More or less on the BBC World Service. Twenty years ago at the Earth Summit in Rio, 172 governments met to debate global warming. They also opened a convention, now signed by 193 nations, to protect the world's biological diversity. Choosing a name for it was pretty easy. It's called the Convention on Biological Diversity. Actually, protecting diversity has of course, proved to be a lot more difficult. You know, the dodo, the Falkland Islands wolf, the golden toad, although they were

[Georgina Mace]

all extinct before the Convention on Biological Diversity was created. More relevant examples are the Pyrenean ibex and the Baiji river dolphin.

[Tim Harford]

Ah, Ruth Alexander's here. Just when I thought you were extinct, Ruth. Anyway, thanks. Yes. The Baiji river dolphin, the Pyrenean ibex, the panda.

[Georgina Mace]

Pandas aren't extinct.

[Tim Harford]

It's just a matter of time, isn't it? They've got it coming. Ridiculously impractical creatures.

[Georgina Mace]

We're not here to disrespect one of the world's cutest species.

[Tim Harford]

No, we're not. This is serious. I know it's serious because I spoke to the top man at the Convention on Biodiversity, but Braulio Diaz, it's a big problem.

[Braulio Dias]

We know from certain sources of data that species extinction has increased in rate in recent times. So we know it is a problem. And we know that the drivers behind the species loss are mostly increasing. So land conversion and degradation, pollution, climate change, all these drivers are still around and increasing. And of course human population is still growing and consumption is growing and mobile. Most of that consumption is not sustainable.

[Georgina Mace]

So there's a problem. And we're here to figure out how big a problem it is. How many species are actually going extinct?

[Tim Harford]

Now, the Convention on Biological Diversity does put a number on it. Here's a quote from Brauley ODS Special Advisor Ahmed Joghlav from the convention's website.

[Ahmed Joghlav]

We are indeed experiencing the greatest wave of extinction since the disappearance of the dinosaurs. Every hour three species disappear and every day up to 150 species are lost.

[Georgina Mace]

Doesn't that suggest there are 50 hours a day?

[Tim Harford]

Up to 50 hours a day, yes. I asked Ahmed Droglav's boss, Braulio Dias, whether he could produce some slightly more rigorous numbers. And it turns out this isn't an easy question to answer.

[Braulio Dias]

We started to identify species in a more scientific approach since Linnaeus about 250 years ago, and we're still doing it because current estimates of number of species can vary from, let's say, 2 million species to over 30 or even 100 million species. So we even don't have a good estimate to an order of magnitude of precision.

[Georgina Mace]

I went to meet Georgina Mace at London's Natural History Museum. She's a professor in the Centre for Population Biology at Imperial College London. And she accepts there's a lot we don't know.

Let's say there are somewhere around 7 to 10 million species on the Earth. That's an estimate we don't know exactly. Of those, we've described less than 2 million. So the rest we don't know what they are. They have no names, we don't have descriptions of them.

[Tim Harford]

And if we didn't know a species existed in the first place, we can hardly notice when it's gone.

[Georgina Mace]

So there are two things you could do about that. You could create a mathematical model, or as Georgina told me, you could count what you know has gone extinct, even though you may well miss a lot.

The iucn, the International Union for the Conservation of Nature, has for many years maintained a list of threatened species. Now, if they're no longer around, they're called extinct. They've rolled off the end of that ladder to extinction, if you like. It's probably pretty good for birds and mammals. There's been a big effort over the last few years to ramp it up for amphibians and reptiles, but it's woefully inadequate. So that approach is never going to get us the answers we need.

Now, the IUCN has A list of 801 species which have gone extinct.

[Tim Harford]

And last week I thought it was 150 a day.

[Georgina Mace]

No, 801 extinct species since the year 1500. Mostly animals, a few plants. But remember, this list comes from the subset of known species, not from the huge variety of unknown species out there, which, as Bralio deer said, could be up to 100 million.

[Tim Harford]

Which makes it sound like the whole thing's complete guesswork.

[Georgina Mace]

Georgina, it's not exactly guesswork, it's modelling.

[Tim Harford]

Now, that model applies something called the species to area relationship to habitat loss. The simplest possible way to describe it is like an estimate is made of the number of species in a given area or habitat. The larger the area, the greater the number of species are said to be in it. Then the model gets worked Backwards, the smaller the area, the fewer species are said to be in it. In other words, if you measure habitat loss, you can calculate using the model how many species must be being lost in that area, even if you don't know what those species actually are.

[Georgina Mace]

It's this model which has generated some very alarming numbers. But more recently it's also generated a mathematical, mathematical row, thanks to this man.

[Stephen Hubbell]

My name is Stephen Hubble and I'm a distinguished professor at the University of California, Los Angeles.

[Georgina Mace]

Professor Hubble thinks that let's call him Stephen. Stephen thinks the species to area relationship model relies on poor maths. And as a result, he says there's a problem.

[Stephen Hubbell]

Well, for the past 40 years people have been using a method that we show is biased and it's biased too high, I.e. it overestimates the extinction rate. The basic problem is that there is an expected relationship as you increase area with an increasing number of species found in the area. And people thought, well, it's straightforward just to run that curve backwards. Reduce the area as if you were cutting down forest and losing habitat to find out how many species would be left. Well, it turns out that the method, when extrapolated backward, doesn't take into account the fact that you need to remove more area to get the whole range of a species. Then you need to remove area to find the first individual of species.

[Georgina Mace]

In other words, Stephen says the model assumes that if you add say a hectare to your five hectare field, then you'll find say five new species. And that that means that if you reverse the process and shrank the field, you'd lose five species. Stephen says that's not how it works, that in fact you need a larger area to eliminate a species than you do to discover one. He says if you correct the mistake in the model, you, it shows about half as many species are going extinct.

[Tim Harford]

And Professor Hubble did make, Stephen did make another interesting point about what kinds of species we're talking about in all this. He said that while many of us thinking about extinction might have in mind so called charismatic animals like rhinos or whales or those ridiculous pandas, in fact, the overwhelming majority of species in the world aren't like that. Braglio Dias agrees with Stephen Hubble that we shouldn't focus too much on big furry animals. And, but even so, it was striking that when I asked him to name something that had actually gone extinct in the last few years, he struggled.

[Braulio Dias]

I can give you example of Brazil, where I came from. We have some species of macaws that are very threatened. There's one particular species called the spix macaw, where the population went extinct in nature. Fortunately, there are still a few individuals kept in captivity and reproducing, so there's still hope in the future to increase their numbers and be able to return them to the wild habitats.

[Tim Harford]

However you look at all this, it's obvious that no one can safely quantify what's going on. When Ahmed Joghlav from the Convention on Biological Diversity told The Every hour, three

[Ahmed Joghlav]

species disappear, every day, up to 150 species are lost.

[Tim Harford]

He couldn't possibly know that to be true.

[Georgina Mace]

But let's be clear. Everyone we've spoken to in researching this item thinks there is a problem, and that includes Stephen Hubble, who says he worried about whether disputing the numbers would make people complacent about species loss. In the end, though, he thought it was more important to share what he'd found.

[Stephen Hubbell]

My bigger worry is that scientists not use flawed methods. So when you find a mistake, you are, as a scientist, obligated to notify everyone that we've made a mistake and we need to fix things. And so, yes, there's been a reaction from my colleagues about this. We were warned by some of them not to publish our paper, but that's not advice that I felt I was morally able to take.

[Tim Harford]

Stephen Hubble of the University of California, Los Angeles, if you see a fact you'd like us to check out, or a fascinating statistical odyssey on which you'd like us to embark, drop us an email at more or lessbc.co.uk. our website is bbcworldservice.com More or less the place to subscribe to our podcast. Or you could simply tune in same stat time, same stat channel next week. Goodbye. More or Less was presented by me, Tim Harford, the undercover economist at the Financial Times. The producer was Richard Knight and the editor, Richard Varden.

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