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An article in Nature, "Global human-made mass exceeds all living biomass" in 2020 has recently gained some attention on social media (see this Twitter thread) possibly because of a striking visualisation of the data.

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The claim, if true, is certainly striking but, I suspect, many of the numbers are based on inherently vague sources. So, despite the claim appearing originally in a prestigious journal,is it a plausible or reliable claim?

Fizz
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matt_black
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    I'm struggling to see how this could be answered without the answer primarily comprising original research. I think all that is to be done is to understand the assumptions the paper makes which is just a matter of reading the actual paper, and checking their math which seems a bit trivial. – Bryan Krause Dec 02 '21 at 17:31
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    When you say human made objects are you counting objects made from biomass that could still be counted as biomass after they are made? – Joe W Dec 02 '21 at 17:34
  • @BryanKrause One could compare the assumptions the paper makes with other reasonable assumptions. And check whether the references used are plausible and themselves make reasonable assumptions. Even search for alternative estimates or criticisms of this paper. Comparing multiple sources is not original research, it is basic skeptical analysis. – matt_black Dec 02 '21 at 17:39
  • @JoeW I'm not saying it: i'm reporting the claim. The source details what they mean in some depth. I think what you say is covered there. – matt_black Dec 02 '21 at 17:40
  • How would you count a mine, Mt. Rushmore, or an oil well (creations that are dependent on *removing* mass? A pile of stones making a vague wall (really heavy but not "made" by some definitions)? Never mind checking the numbers in the paper. The claim itself is trivial, whether true or not, and necessarily based on arbitrary definitions of "human-made". –  Dec 02 '21 at 18:09
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    After pursuing the paper, they're even counting gravel (I guess roads and foundational substrate?), so it's really no surprise it's a literally massive number. Makes one wonder when an abandoned gravel road ceases to be "a man-made object" and starts being rocks again. –  Dec 02 '21 at 18:15
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    Plastics being lightweight, it's really far more surprising the paper claims the total mass of all plastic is *double* that of all animals. –  Dec 02 '21 at 18:16
  • @fredsbend The claim is getting attention for being shocking and, among greens, a huge indictment of human planetary destruction. Questioning their definition of what they consider to be "human made" is a reasonable skeptical approach. If their definition is crazy wide, their claim is a bad claim. – matt_black Dec 02 '21 at 18:18
  • @fredsbend That plastic claim struck me as pretty odd as well. I should have included it as an example in the question (might do later). – matt_black Dec 02 '21 at 18:19
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    Fair point. Never underestimate people's ability to apply gravity to issues that really have none. (see what I did there?) I take back that it's trivial, in light of the response. –  Dec 02 '21 at 18:20
  • I think it is an important part of the claim as some man made things are classified as bio mass and could fall into both categories – Joe W Dec 02 '21 at 18:26
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    To make my comment more clear, the problem is that the answer is entirely based on a combination of 1) trivial math, 2) estimation, and 3) definitions of human-made/biomass. (1) isn't interesting unless there is an arithmetic error, (3) isn't really related to skeptics, anyone can operationally define these things any way they like, to interpret you just have to know how they've done it and anyone can quarrel with any choice made, it's arbitrary. (2) is similar, though you could ask a specific question about a specific estimate the title question relies on many of these rather than one claim. – Bryan Krause Dec 02 '21 at 19:12
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    The article says: *Anthropogenic mass is defined as the mass embedded in inanimate solid objects made by humans (that have not been demolished or taken out of service, which we define as ‘anthropogenic mass waste’).* But gravel, for example, isn't made by humans. It is rock which has been excavated and/or crushed, yet they list **aggregates** and similarly **asphalt**. And in the case of concrete (which is made with aggregates) are they including the gravel *twice*? Mineral oil too, isn't manufactured, but extracted and refined. Do oil, coal and peat count as 'biomass'? – Weather Vane Dec 03 '21 at 07:11
  • @fredsbend Yeah, I suspect this revolves around definitions of "made". Even for stuff like cement / concrete (which I suspect is a large amount of that) it's a bit debatable, even though that clearly involves more processing than for gravel or sand (both of which are part of concrete, besides cement). A quick google search finds something like "A typical concrete mix contains 60 to 80 percent sand and gravel." – Fizz Dec 03 '21 at 09:50
  • @WeatherVane: "**embedded** in inanimate solid objects made by humans" is how they capture gravel (and sand) in their def, as "aggregates" like sand and gravel are the larger part of a concrete mix by weight; see brief quote in my comment above. – Fizz Dec 03 '21 at 09:56
  • @WeatherVane: and oil is no longer **living** biomass according to their def, although that's also slightly debatable as some bacteria do live in oil https://www.sciencedirect.com/science/article/pii/S1871678418316935 – Fizz Dec 03 '21 at 10:04
  • Frankly I'm not sure how they came up with 900Gt of trees when [the paper](https://www.pnas.org/content/115/25/6506) they cite for that seems to give half the figure at 450Gt. Might be an issue of dry vs wet or the latter paper using "Gt C", i.e. gigatons *of carbon*. Apparently it's C->dry conversion "All of our reported values can be transformed to dry weight to a good approximation by multiplying by 2, the characteristic conversion factor between carbon and total dry mass." – Fizz Dec 03 '21 at 10:44
  • Why is this so unbelievable. Your car weighs more than a tonne. Your house could weigh a few hundred tonnes. Add in your share of the buildings where you work and shop, and the roads and sidewalks you use, and the various utilities infrastructure, and so on. – Ray Butterworth Dec 08 '21 at 03:07
  • @RayButterworth The UK is a fairly crowded country. But only ~6% of land is actually built on. And there are a huge number of non-human animals. It is far from obvious that, because a typical human has a huge mass of non-living artefacts, the total human artefact mass exceeds all the biomass. – matt_black Dec 08 '21 at 10:35

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