To quantify all this stuff, the team scoured existing literature, aggregating previously available data sets covering the extraction of resources, industrial production, and waste and recycling. “It turns out that things that humans produce—in our industries, etc.—is something that has been relatively well characterized,” says Weizmann Institute of Science systems biologist Ron Milo, coauthor on the paper.

Quantifying the biomass of all the organisms on Earth was trickier, on account of the planet not keeping good records of exactly how much life is out there. The researchers had to tally everything from giant species like the blue whale all the way down to the microbes that blanket the land and swirl in the oceans. “The biggest uncertainties, actually, in the overall biomass, is in respect mostly to plants, mostly trees,” Milo adds. “It’s not easy to estimate the overall mass of roots, shoots, leaves.” But here, too, Milo and his colleagues could pull from previous estimates of biomass up and down the tree of life and incorporate data from satellite monitoring of landscapes to get an idea of how much vegetation is out there.

They also considered the change in biomass over time. For instance, they note that since the first agricultural revolution, humanity has been responsible for cutting plant biomass in half, from 2 teratonnes to one. At the same time—particularly over the past 100 years—people have been creating ever more anthropogenic mass. Not only has production been increasing exponentially, but as that stuff reaches the end of its usefulness it’s simply discarded if it isn’t recyclable.

In other words, all that crap is piling up while humanity continues to obliterate natural biomass, to the point where the mass of each is now about equal. “They produce this, I think, very eye-catching and also strong message that these two types of stocks—the biomass stock and anthropogenic mass—they are actually at a crossover point more or less in 2020, plus or minus a couple of years,” says social ecologist Fridolin Krausmann of the University of Natural Resources and Life Sciences, Vienna, who wasn’t involved in the research but was a peer reviewer for the paper.

The two stocks turn out to be intimately intertwined. The relentless destruction of biomass is largely a consequence of deforestation in pursuit of industrialization and development. But our built environment is also generally awful for wildlife: Highways slice ecosystems in half, birds fly into buildings, sprawling developments fester like scars on the landscape.

The buildup of anthropogenic mass is also linked to the climate crisis. The production of materials is extremely energy-intensive, for one. In the case of cement production, that climate effect comes from powering the manufacturing process and also from the chemical reactions in the forming material that spew carbon dioxide. If the cement industry were a country, according to the climate change website Carbon Brief, it’d be the world’s third most prolific emitter.

As economies the world over continue to grow, humanity has locked itself into a vicious cycle of snowballing the growth of anthropogenic mass. “On the one hand, economic growth drives the accumulation of this mass,” says Krausmann. “And on the other hand, the accumulation of this mass is a major driver of economic development.” China has been a particularly big contributor as of late, Krausmann adds, as the nation has rapidly and massively built up its infrastructure. Which is not to lay the blame on any one country—we’ve made this mess together as a species. And the modeling in the Nature paper was global, not on the scale of individual nations. “But I think it would be interesting to study that in the future, and really see those changes in different regions or in specific countries,” says Elhacham.

What’s abundantly clear at the moment is that anthropogenic mass has grown unchecked and become a nefarious crust over the planet. “This exponential growth of the anthropogenic mass cannot be sustainable,” says Krausmann, “even though we don’t know exactly where the threshold might be.”

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