Study: Humans 0.01% of World’s Biomass, Cause 83% of Extinctions


The world’s population of 7.6 billion humans represent only 0.01% of earth’s biomass, but contribute to 83% of extinctions and have caused domesticated mammals to represent the 60% of earth’s mammals

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Story Transcript

GREG WILPERT: It’s The Real News Network. I’m Greg Wilpert, joining you from our studios in Baltimore.

The world’s population recently reached 7.6 billion humans this month. Even though this number sounds incredibly large, a recent study of the relative weight of different forms of life on Earth found that humans make up only 0.01 percent of all living matter, or biomass. The vast majority of all life is plant life, actually, which makes up 82 percent of all biomass. The study also found that cultivated animals, such as poultry, cattle, and pigs, make up 60 percent of all mammals. Finally, despite humans being a very small representation in terms of biomass, they can be held responsible for the extinction of 83 percent of all mammal species and 50 percent of all plant species. The study, which is titled “The Biomass Distribution on Earth,” was published in May by the Proceedings of the National Academy of Sciences. It was authored by Yinon Bar-On, Rob Phillips, and Ron Milo.

Joining me now from Tel Aviv, Israel to discuss this study is Ron Milo. Ron is a professor at the Weizmann Institute of Science, where he studies the cellular highways of energy and carbon transformations in quantitative terms, both within the living cells and in the global environment. Thanks for joining us today, Ron.

RON MILO: My pleasure.

GREG WILPERT: So, what, to you, is the most surprising finding of the study?

RON MILO: So, in this census of life that we did we found several things that surprised me. One was whenever you ask a biologist, I just did it last week when I was giving a seminar to Princeton, what is the most abundant thing on earth? Is it plants, or bacteria, or animals? The majority of people would say it’s bacteria. And we found, after doing a quantitative survey, that it’s actually plants, as you mentioned before. Similarly, when I would think about, for example, birds, and you would, and you would ask the question, what do we have most in the world? Is it wild birds, like in the big flocks that we see on nature films? Or is it the domesticated birds? My tendency would be to think that it’s the wild birds that we see in flocks. But what we found, which surprised me, was it is threefold more biomass of domesticated birds, mostly in the form of chickens, which outweigh all wild birds combined together. So these were just two of the things that surprised me.

GREG WILPERT: So the study focused only on the relative weights of different types of living matter, or biomass, on earth. However, given what we know about human activity on Earth, what does your study allow us to conclude about how humans have shaped life on Earth?

RON MILO: Yes. We were looking at the absolute values, in terms of mass of basically every living form on Earth, and made our estimates on that. And we could also compare that to what are the best estimates to what was on Earth before humans came into the scene. And what we could find is that the overall biomass has already been halved. So we only have one half of what used to be in terms of the total biomass. That’s mostly because of clearing of forests in order to make place for agriculture and for grazing areas.

And the other thing is when we’re looking at, for example, wild mammals, we found the amount of wild mammals that we have left is only about one fifth of what it used to be. So somewhere around 80 percent of the mass of wild mammals is already lost, and we have only the remaining.

GREG WILPERT: So presumably you did not go around weighing, or even counting, every form of life. And your definition, like you mentioned, you also include bacteria, and even viruses. So how, in general terms, did you figure out the relative biomass of all life?

RON MILO: So what we did is what’s known as meta meta analysis, meaning that indeed we did not go into every corner of the earth and did all the measurements. We based our survey on many, many different studies, hundreds of different studies, each one collecting values from many locations around the earth, be it in the oceans or be it on land, and we integrated all of that information together. And the fantastic student Yinon Bar-On in his Ph.D. work found ways in order to extrapolate from the many measured points, also find mathematical relationships about the points that were not yet measured. And when you integrate over all that, you get the best values that we could report in the Proceedings of the National Academy of Sciences.

GREG WILPERT: So what are some of the, what you would say, are the more notable conclusions from your study? I mean, what, what does this allow you to conclude, and what makes it significant?

RON MILO: So it gives us a holistic picture of what exists on Earth. And there we could see, for example, that if you compare the mass of wild animals, that of humans and livestock, we see there’s about 30-fold more mass of domesticated mammals than old wild mammals combined. So for example, I have three small daughters at home, and I often read them a book about animals, or do a puzzle together. In the puzzle usually you have, like, an elephant next to a giraffe next to a deer. It now makes it clear to me that if we had to do it realistically, it would be a cow next to a cow next to another cow, and maybe be a pig somewhere, and a person.

So I think it gives us a new perspective on, you know, what we have on planet earth right now, and therefore maybe what we want to make sure to take care of. So that’s maybe one perspective. Another perspective that came out with regards the issue of how pyramids, biome pyramids are built. There is this notion of the ratio between how much consumers and how much producers there are. And through our study we found that in the oceans the pyramid of different life forms is very different from what we thought before.

GREG WILPERT: Can you say a little bit more about that? I mean, what is exactly different with the oceans and what we normally assumed?

RON MILO: So it’s a bit counterintuitive, but if you look on land, right, you would find that there’s more consumers than producers. You have many more animals, and it is much more mass of plants than the animals that feed on them. But in the marine environment, in the oceans, what we could show is that you have what’s known as an inverted pyramid. The picture is reversed. You have more biomass of fish and similar organisms in respect to what’s known as phytoplankton, the organisms that produce the energy from taking the sun. And this is a result of the fact that they are very productive and they live for a very brief period of time. They usually live for just a few days, whereas the fish that feed upon them live for several years, and therefore you have this inverted pyramid of the standing stock of of these lifeforms. So that gives a new perspective on the structure of life in our oceans.

GREG WILPERT: So just to conclude, I mean, what is some of the things that you would say in terms of the effect, or the impact, that humans have had on the planet? We already mentioned the extinctions. But in terms of, also, the large number of domesticated mammals, what would you conclude from that? I mean, based on what you’ve studied.

RON MILO: Yes. So we would conclude that even though in terms of mass we’re a pretty small fraction, about 0.01 percent, that is, one in ten thousand part, in terms of our impact on the biosphere it’s already pretty overwhelming in terms of decreasing the overall biomass by a factor of two, decreasing the mammalian biomass of all wild things by about a factor of six. So we already have very, very significant impact. It’s also what’s denoted is like a new geological era known as the anthropocene, meaning that we’re like in a geological period where we are a force of nature. And I think this gives us some food for thought about, you know, how much we consume, how we consume it, you know, how we produce our food. All of those things that have a big impact through us on land, on water, and on all living things.

GREG WILPERT: Yes, I guess that gives a new idea as to what it really means to be living in the anthropocene. But we’re going to have to leave it there for now. I was speaking to Ron Milo, co-author of the study “The Biomass Distribution on Earth.” Thanks again, Ron, for having joined us today.

RON MILO: Thank you. All the best.

GREG WILPERT: And thank you for joining The Real News Network.