Since the start of the twentieth century, extraction of iron ore around the world has increased more than thirtyfold; its yellow line on the graph above rises slowly during the first half of the 1900s, gets steeper during the 1950s, then finally shoots dramatically to the top of the Y-axis in the 2000s. In the same timeframe, global carbon dioxide (CO 2 ) emissions have increased more than fifteenfold, while water use, coal production and crop harvests have each increased between five- and tenfold. To follow the upward curves on the graph is to trace the some of the grandest growth spikes in modern history.

Societies, like organisms, have metabolisms. They require inputs of raw materials and energy, which are consumed or sometimes stored. Consumption of those materials also produces waste and emissions (also charted above). According to recent estimates, the global population will use nearly 90 billion tons of raw materials in 2018. Depending on the degree to which policies are put into place to favor remanufacturing, reuse and recycling, that consumption is projected to increase to between 150 billion and 180 billion tons by 2050, revving up the globe’s metabolism.

“Most of our current environmental problems or sustainability challenges ... are somehow related to this type of metabolism,” says Fridolin Krausmann, a sustainability researcher at the Institute of Social Ecology in Vienna, Austria. As global resource use nearly doubles in the coming years, so, too, will the pressures on the environment as well as conflicts over access to limited resources, Krausmann and his coauthors warn in the 2017 Annual Review of Environment and Resources, where this graph originally appeared.

In keeping track of the world’s resource inputs and waste, researchers find that countries undergo predictable metabolic transitions as they develop: The economies of low- and middle-income countries rely mostly on renewable biomass such as crops, and as they industrialize, their economies shift to nonrenewable resources such as fossil fuels and minerals. For instance, crop harvests and water extraction rose slowly and steadily in the first half of the 1900s, but beginning around 1950, iron ore extraction and CO 2 emissions show a rapid increase. That trend was caused by industrialization in high-income countries in Europe and North America after World War II, Krausmann says.

The next massive spike in iron ore extraction and CO 2 emissions occurred around the year 2000, reflecting the “massive growth” in emerging economies like China, which was developing a steel industry and investing in large infrastructure projects at the time. They, like the postwar countries before them, were shifting to higher metabolisms, which caused them to consume more nonrenewable resources and produce more waste.

Today, many low- and middle-income countries are similarly transitioning toward a more industrialized metabolism. But in high-income countries in Europe and North America, as well as Japan, where this transition has already occurred, resource extraction per capita is actually going down. It’s not that they’ve stopped consuming, but rather that these countries are relying more and more on resources extracted elsewhere in the world and then imported. In other words, rich countries are increasingly outsourcing the environmental impacts of their growth.

It’s unclear if such practices can be sustained, especially as emerging economies transition to fully industrialized and urban societies themselves. China, for example, was a net exporter of raw materials until about the year 2000; today, the country has become a net importer because of the huge uptick in domestic demand for resources such as iron needed to forge its fast-growing energy and transportation projects.

In addition to sustainability challenges, resource scarcity can also drive human conflicts. For instance, as Europe farms out metal extraction activities to countries such as Peru and Chile, land-related conflicts with indigenous peoples in Latin America have become more acute. Similarly, Europe’s high consumption of textiles imported from South Asia contributes to worsening water scarcity in Pakistan and India (growing cotton and dyeing and processing textiles require a lot of water). That scarcity in turn fuels conflicts over access to water.

“Given that we are already touching the planetary boundaries in many respects, I think that developing alternative models is urgently needed to avoid an ecological disaster in the long run,” says Stefan Giljum, an ecological economist at Vienna University of Economics and Business in Austria.

One alternative model is called the “circle economy.” Researchers envision a secondary metabolic transition in which more recycling could help stabilize a nation’s appetite for nonrenewable resources. For instance, 70 percent of steel is currently recycled and reused in the process of steelmaking, which reduces the demand for raw iron ore. In contrast, only about 1 percent of specialty metals found in cell phones, computers and batteries are recycled. By creating facilities to recycle those materials and keep them out of landfills, countries could reduce their metabolic input. Another tenet of a circle economy is “downcycling” — for instance, using the broken concrete from demolished buildings to make roads, thus reducing the amount of primary resources such as sand and gravel needed.

In the long term, circle economies could potentially reduce dependence on imports as well as environmental impacts, Giljum explains. That’s important, especially as other world regions develop and increase their demand, leading to increased competition for those limited resources. Developing a circle economy isn’t just good for the environment either, adds Heinz Schandl, an industrial ecologist at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Canberra, Australia. It also provides economic advantages.

China, for instance, has a circle economy policy and is investing heavily in renewable energies and public transport. Schandl predicts that those investments will create a competitive advantage in the decades to come, both in terms of economic growth and employment, compared with countries that continue to adhere to old industrial patterns. In theory, once China’s infrastructure for its circle economy is established, its material flows should stabilize or even decrease — but it’s hard to predict exactly when, or even if, that might happen. The quantities of raw materials flowing through China today are staggering.

“We’re talking about 1.3 billion people moving from one way of living — pre-industrial, agriculture-based — to a new model which is industrial and urbanized, needing more resources and creating more waste,” Schandl says. “That’s something that has never happened before at that scale and speed, and we see it in the global numbers.”