A rough assessment . . . shows that current appropriations of natural resources and services already exceed Earth’s long-term carrying capacity. . . . If everybody on Earth enjoyed the same ecological standards as North Americans, we would require three earths to satisfy aggregate material demand, using prevailing technology. . . . To accommodate sustainably the anticipated increase in population and economic output of the next four decades, we would need six to twelve additional planets. —MATHIS WACKERNAGEL AND WILLIAM REES, 1996
