Copper helps makes the modern world go. You use it every time you flick a light switch, drive a car, make a phone call, or send an e-mail. But fresh stocks won't be available forever. A team of researchers has calculated that if the entire world begins using copper at North American rates, we'll have mined it all in less than 50 years.
Humans have quarried copper for nearly 7000 years. Originally used for tools, weapons, and jewelry, the shiny orange metal became particularly valuable in the 20th century as an electrical conductor. Although it's essential for today's technologies, the amount of copper available in Earth's crust is limited. Sooner or later, recycling will be the only way to get it.
To figure out just when this will happen, industrial ecologist Thomas Graedel and colleagues at Yale University in New Haven, Connecticut, used two approaches. First, they calculated the total amount of copper mined in Canada, Mexico, and the United States during the 20th century, subtracted the amount lost to waste, and assumed the remainder was the total amount of copper in use today in North America. According to the researchers, this is a good estimate because North America imported very little copper during the 20th century. The second method added up all the copper in New Haven, Connecticut. In both methods the total amount of copper in use in the areas was divided by the respective populations--either all the people in North America, or all the people in New Haven --to get an average copper use per person.
The two averages agreed fairly well: There are about 150 kilograms of copper in current use for each person in North America. The researchers then multiplied the copper used per person by total world population, using standard population estimates to project into the future. By the mid-21st century, if everyone in the world used copper at North American rates, every scrap of known copper ore would be mined, the team reports online this week in Proceedings of the National Academy of Sciences.
"This is the first study of its kind, and they're doing the best one can do with what we know right now," says Matthias Ruth, an industrial economist at the University of Maryland in College Park. He says no previous analysis has looked at copper stocks over an area as large as North America, or for as long a time period as the whole 20th century. Still, Graedel cautions that his study does not look at whether the world actually has enough energy, water, and infrastructure to mine all of the metal people may eventually require. He predicts that for both economic and environmental reasons, the world may have to make do with significantly less copper per person than North American uses now.