Humans Have Bogged Down the Earth with 30 Trillion Metric Tons of Stuff, Study Finds

Humans have produced a lot of stuff since the mid-20th century. From America's interstate highway system to worldwide suburbanization to our mountains of trash and debris, we have made a physical mark on the Earth that is sure to last for eons. Now a new study seeks to sum up the global totality of this prodigious human output, from skyscrapers to computers to used tissues.

That number, the researchers estimate, is around 30 trillion metric tons, or 5 million times the mass of the Great Pyramid of Giza. And you thought you owned a lot of crap.

The researchers refer to this tsunami of manmade stuff as the “technosphere.” The term "is a way of helping people recognize the magnitude and pervasive influence of humans on the planet," says Scott Wing, a paleobotanist at Smithsonian’s National Museum of Natural History and a co-author on the study published last week in the journal The Anthropocene Review. Wing is part of a group of scientists and climate leaders seeking to define a new geologic epoch reflecting the significant impact humans have had on Earth, known as the Anthropocene.

Part of defining a new epoch involves delineating its physical outlines in the Earth's layers of rock. As sediments build up over time, often with fossils and other remnants of life packed within, they provide a kind of timeline of the history of the Earth. For example, scientists were able to theorize that a large asteroid impact had wiped out the dinosaurs at the end of Cretaceous period years before finding the asteroid's crater, because they found a larger than normal amounts of iridium within sedimentary layers around the world. (Iridium is rarely found on Earth, but is much more common in comets and asteroids.)

Stratigraphers—geologists who study the strata, or layers, of the Earth—are used to thinking in time spans of millions of years, not decades. But the Anthropocene Working Group is urging the scientific community to recognize that humans are impacting the planet in unprecedented ways, and that it is time to formally recognize how significant that is. "We are now in some ways rivaling the great forces of nature in terms of the scale of our influence on the surface of the planet," Wing says.

To get a sense of that scale, members of the AWG set out to broadly estimate the mass of stuff that humanity has produced thus far. Using satellite data estimating the extent of various types of human development on the land, from cities and suburbs to railroad tracks, the researchers estimated (very roughly) that the physical technosphere comprises 30 trillion metric tons of material, and is spread over roughly 31 million square miles of Earth's surface.

In Earth’s biological ecosystems, animal and plant waste are generally reused by other organisms in an efficient cycle of life. "In the biosphere, there's no trash," Wing says. "The things that we produce become waste because there’s no part of the system that recycles those back to their original condition." Much of the material in the technosphere, by contrast, ends up in landfills where it often doesn’t decay or get reused.

This is exacerbated by the fact that humans today use up stuff very quickly. (Just think of how many new phones your friends have bought in the past few years.) "The evolution of the technosphere is exceedingly fast," says Jan Zalasiewicz, a paleobiologist at the University of Leicester in Great Britain and lead author on the new study. "Far faster than our own evolution."

Not all are convinced by the researchers’ interpretation, however. University College London climatologist Mark Maslin takes issue with the study, calling its methodology "incredibly weak." "I can pick holes in about half the numbers [in the study]," Maslin said. One example he offers is how the study uses an average density for cropland that is higher than the density of water.

Maslin and several other scientists published broader critiques of the efforts of the Anthropocene Working Group yesterday in the journal Nature. Though they agree that the Anthropocene should be considered a geologic epoch, they argue that the process of defining it as such should be much more transparent and should focus more on human impacts before 1950.

"They [the Anthropocene Working Group] instill a Eurocentric, elite and technocratic narrative of human engagement with our environment that is out of sync with contemporary thought in the social sciences and the humanities," Maslin and his colleagues wrote in their critique. "Defining a human-centered epoch will take time. It should be treated by scholars from all disciplines with the seriousness it deserves."

Wing and his co-authors acknowledge that their study's calculation is a very rough estimate. But they say that it is meant to help people think about how humans have produced nearly 100,000 times their mass in stuff to support our continued existence. "People will go 'wow,'" Wing says. "And maybe they’ll even take it a step further, and think about the trillion tons of carbon in the atmosphere that we put there."

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Ben Panko is a staff writer for Smithsonian.com