Julian Simon was a senior fellow at the Cato Institute and a professor of business and economics. In his book The Ultimate Resource 2 (first printed in 1981 and reprinted in 1998), he extensively criticizes the notion of "peak resources", and uses copper as one example. He argues that, even though "peak copper" has been a persistent scare since the early 20th century, "known reserves" grew at a rate that outpaced demand, and the price of copper was not rising but falling over the long run. For example, even though world production of copper in 1950 was only one-eighth of what it was in the early 2000s, known reserves were also much lower at the time – around 100 million metric tons – making it appear that the world would run out of copper in 40 to 50 years at most.
Simon's own explanation for this development is that the very notion of known reserves is deeply flawed, as it does not take into account changes in mining profitability. As richer mines are exhausted, developers turn their attention to poorer sources of the element and eventually develop cheap methods of extracting it, raising known reserves. Thus, for example, copper was so abundant 5000 years ago, occurring in pure form as well as in highly concentrated copper ores, that prehistoric peoples were able to collect and process it with very basic technology. As of the early 21st century, copper is commonly mined from ores that contain 0.3–0.6% copper by weight. Yet, despite the material being far less widespread, the cost of, for example, a copper pot was vastly lower in the late 20th century than 5000 years ago.