Ehrlich was the author of a popular book, The Population Bomb, which argued that mankind was facing a demographic catastrophe with the rate of population growth quickly outstripping growth in the supply of food and resources. Simon, a libertarian, was highly skeptical of such claims.
The face-off occurred in the pages of Social Science Quarterly, where Simon challenged Ehrlich to put his money where his mouth was. In response to Ehrlich's published claim that "If I were a gambler, I would take even money that England will not exist in the year 2000" — a proposition Simon regarded as too silly to bother with — Simon countered with "a public offer to stake US$10,000 ... on my belief that the cost of non-government-controlled raw materials (including grain and oil) will not rise in the long run."
You could name your own terms: select any raw material you wanted — copper, tin, whatever — and select any date in the future, "any date more than a year away," and Simon would bet that the commodity's price on that date would be lower than what it was at the time of the wager...
Ehrlich and his colleagues picked five metals that they thought would undergo big price rises: chromium, copper, nickel, tin, and tungsten. Then, on paper, they bought $200 worth of each, for a total bet of $1,000, using the prices on September 29, 1980, as an index. They designated September 29, 1990, 10 years hence, as the payoff date. If the inflation-adjusted prices of the various metals rose in the interim, Simon would pay Ehrlich the combined difference; if the prices fell, Ehrlich et al. would pay Simon...
Between 1980 and 1990, the world's population grew by more than 800 million, the largest increase in one decade in all of history. But by September 1990, without a single exception, the price of each of Ehrlich's selected metals had fallen, and in some cases had dropped through the floor. Chrome, which had sold for $3.90 a pound in 1980, was down to $3.70 in 1990. Tin, which was $8.72 a pound in 1980, was down to $3.88 a decade later.
As a result, in October 1990, Paul Ehrlich mailed Julian Simon a check for $576.07 to settle the wager in Simon's favor.
In 1980, Julian Simon repeatedly challenged environmental scientists to bet against him on trends in prices of commodities, asserting that humanity would never run out of anything... Paul and the other scientists knew that the five metals in the proposed wager were not critical indicators and said so at the time... They emphasized that the depletion of so-called renewable resources — environmental resources such as soils, forests, species diversity, and groundwater — is much more indicative of the deteriorating state of society's life-support systems... Nonetheless, after consulting with many colleagues, Paul and Berkeley physicists John Harte and John Holdren accepted Simon's challenge in late 1980...
It's not clear if Ehrlich consulted with economists. If he had, the flaw in using commodity prices as the best way to understand biophysical limits might have become obvious. Many economists understand the principle of substitution and the dynamic influence of technology with respect to commodity prices. For example, in the absence of any new technologies, copper prices would indeed be expected to increase as growing economies demanded more copper to meet the needs of expanding communications networks and plumbing infrastructure. Technological changes mitigated much of this expected demand as fiber optics replaced copper wire networks and various plastics replaced the once ubiquitous copper pipes throughout the construction industry.
Julian Simon won because the price of three of the five metals went down in absolute terms and all five of the metals fell in price in inflation-adjusted terms, with both tin and tungsten falling by more than half. So, per the terms of the wager, Ehrlich paid Simon the difference in price between the same quantity of metals in 1980 and 1990 (which was $576.07). The prices of all five metals increased between 1950 and 1975, but Ehrlich believes three of the five went down during the 1980s because of the price of oil doubling in 1979, and because of a worldwide recession in the early 1980s.
Yet, it is significant that, according to an article in Wired:
All of [Ehrlich's] grim predictions had been decisively overturned by events. Ehrlich was wrong about higher natural resource prices, about "famines of unbelievable proportions" occurring by 1975, about "hundreds of millions of people starving to death" in the 1970s and '80s, about the world "entering a genuine age of scarcity." In 1990, for his having promoted "greater public understanding of environmental problems," Ehrlich received a MacArthur Foundation Genius Award."
[Simon] always found it somewhat peculiar that neither the Science piece nor his public wager with Ehrlich nor anything else that he did, said, or wrote seemed to make much of a dent on the world at large. For some reason he could never comprehend, people were inclined to believe the very worst about anything and everything; they were immune to contrary evidence just as if they'd been medically vaccinated against the force of fact. Furthermore, there seemed to be a bizarre reverse-Cassandra effect operating in the universe: whereas the mythical Cassandra spoke the awful truth and was not believed, these days "experts" spoke awful falsehoods, and they were believed. Repeatedly being wrong actually seemed to be an advantage, conferring some sort of puzzling magic glow upon the speaker.
Exponential population growth cannot continue indefinitely for any species, whether it exists as microbes in a petri dish, wild salmon at sea, caribou in the taiga, or a global human society. However, world population is no longer growing exponentially; it has been decelerating for the last half century or so, and UN projections show that it may actually decline after 2040.
Simon offered to raise the wager to $20,000 and to use any resources at any time that Ehrlich preferred. Ehrlich countered with a challenge to bet that temperatures would increase in the future. The two were unable to reach an agreement on the terms of a second wager.
Inflation-adjusted price movements of the commodities in the wager between Simon and Ehrlich may be seen in the larger 1950–2002 context in the following chart . Prices were generally rising from 1960 up until 1978, and generally falling thereafter.
The trends they bet would continue to worsen were:
Simon declined Ehrlich and Schneider's offer to bet, and used the following analogy to explain why he did so:
Simon's thesis is that humanity's life-style will continue to improve, and several of the points of Ehrlich's second bet may increase for wholly benign reasons. For instance, the prediction of less agricultural soil per capita is a trend that Simon observed in The Ultimate Resource which Simon attributed to long-term rises in agricultural productivity.
In 1996, Simon bet $1000 with David South that the inflation-adjusted price of timber would decrease in the following 5 years. Simon paid out early on the bet in 1997 (before his death in 1998) based on his expectation that prices would remain above 1996 levels (which they did).
In recent years, there have been many bets and bet challenges related to global warming. For instance, J. Scott Armstrong challenged Al Gore to a climate-related bet in 2007, focused on year-to-year variation in temperatures , but not betting on longer term changes in global average temperatures.