It’s not just your storage unit that’s packed to the gills. According to a new study, the mass of all our stuff—buildings, roads, cars, and everything else we manufacture—now exceeds the weight of all living things on the planet. And the amount of new material added every week equals the total weight of Earth’s nearly 8 billion people.
“If you weren’t convinced before that humans are dominating the planet, then you should be convinced now,” says Timon McPhearson, an urban ecologist at the New School who was not involved with the research. “This is an eye-catching comparison,” adds Fridolin Krausmann, a social ecologist at the University of Natural Resources and Life Sciences, Vienna, who also was not involved in the work.
There are many measures of humanity’s impact on the planet. Fossil fuels have sent greenhouse gases soaring to levels not seen in at least 800,000 years. Agriculture and dwellings have altered 70% of land. And humans have wiped out untold numbers of species in an emerging great extinction. The transformations are so great that researchers have declared we’re living in a new human-dominated age: the Anthropocene.
Systems biologist Ron Milo of the Weizmann Institute of Science went looking for a new gauge of our impact. He and his colleagues synthesized previous estimates of the biomass of living plants for each year between 1900 and 2017. Those estimates account for about 90% of all living things and are based on field research and computer modeling. From 1990 onward, they also include data from satellites, which researchers have used to track global vegetation.
Then the team added in the mass of all other living things—organisms from bacteria to whales—which they had tallied up in 2018, based on field surveys. (Humans make up roughly 0.01% of the planet’s biomass.) The yearly estimates of the mass of humanmade materials came from published research by Krausmann and colleagues, including objects such as cars and machines, and buildings and other infrastructure.
The change over the past 120 years has been dramatic. In 1900, the mass of human materials was just 3% of Earth’s total biomass. Since then, materials have doubled about every 20 years, the team reports today in Nature. The glut of concrete and asphalt began during the boom years between World War II and the oil crisis of 1973, when developed countries went on a building spree. In recent decades, even more has been added. Meanwhile, total biomass declined gradually since 1900 to about 1100 billion tons, because of deforestation and other reasons. The increase is humanmade mass is driven by the use of dense geological resources: rocks, minerals, and metals.
Humanmade mass finally exceeded Earth’s total living biomass this year—give or take 6 years. The timing of that transition hinges on whether biomass is tallied with or without water. If water is included, biomass will remain larger than human materials until about 2037. Even today, the comparisons are sobering: Buildings and other infrastructure weigh more than the world’s trees and shrubs, the researchers found. And the mass of plastic is double that of all animals. The findings add weight to the concept of the Anthropocene, the researchers conclude. “It is an indication that, indeed, the transition happened and the name is appropriate,” Milo says. He doesn’t have a strong opinion on whether the beginning of the new geological era should be this year or decades earlier.
The new research “helps us solidify the evidence of our impact on the planet,” says Josh Tewksbury, director of Future Earth, a network of sustainability scientists. But, he says, “It doesn’t help us on the details of what to do about it.” That’s because global mass of materials is a crude metric of impact. For example, Krausmann says, it doesn’t consider the toxicity of various substances. And location matters, too. The concrete in a dam has a much bigger environmental impact than the same amount of concrete in a city.
Eduardo Brondizio, an environmental anthropologist at Indiana University, Bloomington, points out that in developing countries, where cities lack adequate housing, sewage treatment plants, and other infrastructure, a dearth of human materials is unjust and environmentally damaging. “It’s not that infrastructure per se is bad,” he says. “It’s how we do infrastructure that is the problem.”
Infrastructure will continue to expand, fastest in developing cities, says Xuemei Bai, who studies urban sustainability at the Australian National University. All the energy involved in producing raw materials could jeopardize international climate goals, she notes. But cities offer an efficiency of scale not possible in rural locations, because they have fewer roads and water mains per person, for example. And technological and policy innovation could help reduce the environmental impact of humanity’s massive footprint, Bai says. “I’m hopeful. It is possible.”
sciencemag.org, 9 December 2020