It is widely believed that a nation's metal use plateaus when that country's gross domestic product (GDP) reaches a threshold of $15,000 per person; with rising affluence, the theory goes, nations achieve a new level of resource efficiency.
This might not be the case, a new Yale-led study finds. In an analysis of 43 large economies during the period of 1995 to 2015, a team of researchers found that GDP remains intrinsically linked with metal use even as affluence grows.
According to their findings, published in the journal Nature Geoscience, a 1 percent rise in GDP raises a nation's so-called metal "footprint" by as much as 1.9 percent during the same year.
Breaking this tenacious link between economic growth and metal use will be necessary to ensure global access to metals and a low-carbon future, the authors write.
A society's metal "footprint" includes the use of metal ores, across the supply chain, associated with the production of materials to meet domestic demands. (For instance, when evaluating the total impact of a factory, the metal footprint includes metals associated with the construction of that factory, with the vehicles that transported the materials, et cetera.)
"The metal footprint responds to the economy," said Edgar Hertwich, a professor of industrial sustainability at the Yale School of Forestry & Environmental Studies (F&ES) and senior author of the paper. "We found that a primary short-term driver of this is investments. People invest when things are going well and slow down when they see a recession coming.
"And when the economy grows rapidly, there is a surge in investment in construction and new machinery."
Conversely, they found that the effects of economic decline on metal use demands was twice that of growth -- possibly because consumers delay major purchases or curtail consumption when finances get tight.
The lead author is Xinzhu Zheng of Tsinghua University, who last year was a guest researcher at the Yale-based Center for Industrial Ecology.
"Our study reveals that investment accounted for the high sensitivity of a metal use to economic growth," said Zheng. "In developing countries, such as China, investment-driven development causes substantial metal use. In developed countries, such as the U.S., a stable or even decreasing investment rate resulted in the decoupling of per capita metal footprint from growth."
In the long term, the link between economic growth and metal use is not sustainable, the authors suggest. There are, of course, multiple problems associated with growing global demand for metals, including the environmental consequences of extraction and the long-term potential of metal scarcities. While metals are, in theory, infinitely recyclable, the recycling processes are often hampered social factors, inadequate technologies, product design, and the lack of separation and sorting facilities.
The analysis suggests that such factors as increased recycling, a shift to new construction materials and "saturation" of infrastructure might enable metal use to become decoupled from economic growth.
But current data suggests that that is not the trend currently.
Achieving this decoupling, the authors write, will require innovative solutions and policies. For instance, if the transportation sector one day shifts to a smaller fleet of self-driving vehicles and if builders are able to reduce steel demand by using alternate materials -- like, say, wood-framed buildings -- it could drastically reduce the overall metal footprint.
"Policies targeting material efficiency within construction and manufactured products may allow governments to achieve the desired decoupling of development from metal use and associated environmental impacts," the authors write.