"We have gathered together the information on these metals that is the stock in use," says team leader Thomas Graedel of Yale University. "This tells you how much copper it really takes to provide electricity, plumbing, road systems. We can say considerably better than people have been able to say in the past how much does it take if the world is going to live like a person from a developed country."
Graedel and his colleagues drew on archaeological, historical and modern data to determine how much new copper has been brought out of the ground and into use as well as how much has been discarded over the course of the 20th century. North America alone mined 164 million metric tons of the reddish-brown metal. Then, based on current discovery rates and existing geologic surveys, the researchers estimated that 1.6 billion metric tons of copper exist that could potentially be brought into use. This figure relies on the broadest possible definition of available copper as well as a lack of energy constraints and environmental concerns. In contrast, the U.S. Geological Survey predicts there is only 950 million metric tons of the metal that could be recovered.
"Certainly every square meter of earth hasn't been dug up but there aren't many places that haven't been investigated pretty thoroughly," Graedel notes. "We're not going to suddenly discover a new continent."
The researchers went on to examine per capita use of copper in the U.S. and other developed countries. While some theorists had predicted that metal use would decline as economies advanced beyond building metallic infrastructure, the teams' data showed that overall copper use in the U.S. climbed to a high of 238 kilograms per person by 1999. Declines in areas like manufacturing and railroads were more than offset by increases in areas like motor vehicles and domestic devices. In fact, residents of Canada, Mexico and the U.S. required an average of 170 kilograms of copper per person. Multiply that by overall population estimates of 10 billion people by 2100 and the world will require 1.7 billion metric tons of copper by that date--more than even the most generous estimate of available resources.
The same dynamic also holds true for other critical metals such as platinum, required for catalytic converters and other pollution control devices, and zinc, used to galvanize steel. While iron, aluminum and other more abundant metals could conceivably be used as substitutes, more research would need to be directed into such technology shifts, the team writes in the paper published online this week in the Proceedings of the National Academy of Sciences. And certainly as much currently processed copper, platinum and zinc should be conserved as possible; the world needs it. "Either the rest of the world can't live like the developed world or we need, as a society, to think more about the technology of providing these services with less intensive use of at least certain materials," Graedel explains. "We need to do a more diligent job of good housekeeping."