Human stuff now outweighs all living things

Humanity has crossed an environmental milestone: the total amount of manmade materials has, this year, passed the point where it outweighs all life on Earth. This comes from a calculation by scientists at the Weizmann Institute in Israel, comparing the total dry biomass on the planet to all human-made constructions and materials. It reinforces the idea that we’re living in a new era - known as the Anthropocene - defined by our own changes to the planet. Jan Zalasiewicz is a geologist at the University of Leicester and took a look at the study - which came out in the journal Nature - for Chris Smith...

Jan - It's a very big number: it's a little bit over a trillion tons. Both all the stuff we've made, and also it's the weight of all life on Earth.

Chris - How did they arrive at these figures though? And how accurate are they? How do you go about weighing all of the life on Earth, and then weighing all the stuff we've made?

Jan - They're both sets of estimates; now they're estimates made as rigorously and honestly as possible. Let's say of all the life on Earth... that includes forests, which one can observe by satellite, measure, and the biologists get some idea of how many trees there are, let's say for a square kilometre of ground, and factor that in. There are more calculations: all the fish in the sea, all the bacteria in the soil, all the bacteria in the rocks beneath the soil. Now there are error bars on all of those figures, but taken together, the figures are a reasonable picture. And a very large proportion of the living weight are forests; they make up probably something of the order of 90%.

For the other measurements, the stuff we make, there are statistics around collected by government institutes, government surveys, industrial bodies; on things like the metals we pull out of the ground, the limestone and mud that we pull out of the ground to make cement, which goes into concrete. There are people who collect materials on industrial production. So this team has taken all of those diverse statistics and put them together to arrive at a headline global figure; not just one figure for today, but they've calculated back to the beginning of the 20th century. And one of the extraordinary things they've shown is just how, particularly since the mid-twentieth century, the amount of stuff we made has gone up and up. It's been doubling about every 20 years.

Chris - I was going to ask you how fast it was changing, because obviously the rate of change is the key thing. So that means literally by as soon as 2040, instead of there being 1 trillion tons of human-made stuff, there's going to be 2 trillion tons of human-made stuff. Now you were part of another study, historically, that's actually called the Technosphere study. That was in 2016, wasn't it? And that study attempted to put a weight, or a mass on all the stuff we've moved around on the Earth surface. That was a lot bigger; the results from that study suggested we've scraped up 30 trillion tons of sea floor, made that much concrete, metal, manufactured things and so on. So what's the distinction between that study and this one?

Jan - That's right. We were comparing two different aspects of the way we've changed the Earth. This present study is simply things we've made, but to make those things, you also need to get materials out of the ground. And also when we build things, we landscape the ground. To grow our food, we need to shift soil around. We scrape the sea floor too, when we trawl for fish and so on. So I think the difference between the two studies shows just much we waste, in the course of making all of the stuff we make, all of our constructions.

Chris - What are the take home messages in this? The fact that we can now say the things we've made outweigh all life on this planet? Is the intention of doing this study to make that poignant, very poignant point that we now need to watch this planet over which we have stewardship, because we're making a very serious dent in it?

Jan - Indeed. It's to give us a sense of the scale of what we're doing, which I think we lacked before. And of course there's a price for everything: there's a price in terms of pollution, in terms of the loss of biological species, in terms of global warming, global heating, perhaps of climate change.