First, some background: Twenty-six years ago, in one of the most famous wagers in the history of science, Paul Ehrlich, John Harte and John P. Holdren bet Julian Simon that the prices of five key metals would rise in the next decade. Mr. Ehrlich and his colleagues, all environmental scientists, believed that humankind’s growing population and appetite for natural resources would eventually drive the metals’ costs up. Simon, a professor of business administration, thought that human innovation would drive costs down.


Ten years later, Mr. Ehrlich and his colleagues sent Simon a check for $576.07 — an amount representing the decline in the metals’ prices after accounting for inflation. To many, the bet’s outcome refuted Malthusian arguments that human population growth and resource consumption — and economic growth more generally — would run headlong into the limits of a finite planet. Human inventiveness, stimulated by modern markets, would always trump scarcity.

Indeed, the 1990s seemed to confirm this wisdom. Energy and commodity prices collapsed; ideas (not physical capital or material resources) were the new source of wealth, and local air and water got cleaner — at least in rich countries.

But today, it seems, Mr. Ehrlich and his colleagues may have the last (grim) laugh. The debate about limits to growth is coming back with a vengeance. The world’s supply of cheap energy is tightening, and humankind’s enormous output of greenhouse gases is disrupting the earth’s climate. Together, these two constraints could eventually hobble global economic growth and cap the size of the global economy.