Our Ecological Footprint: Reducing Human Impact on the Earth.

• Author: Runyan, Curtis

In 1400 A.D., the Hohokam, a civilization of nearly 400,000 in what is now Arizona, simply disappeared. The Hohokam had developed one of the first purely agricultural civilizations in North America - in a desert where the average summer temperature is 94 degrees and the average annual rainfall is seven inches. Given the harsh desert climate, it might seem likely that a cyclical drought or some other "natural" disaster was responsible for their disappearance. But the evidence implicates the Hohokam in their own demise: by importing massive amounts of water through an extensive irrigation network of large canals, this rapidly growing society most likely promoted a catastrophic increase in salt levels in their croplands. As their demand for food increased, their fields were gradually poisoned by irrigation, which waterlogged the soils and increased the accumulation of salt beyond the desert's natural capacity to flush the soils clean. While the Hohokam people were able to thrive in the desert for more than 1,000 years, in the end their own growth and nearsighted resource use toppled their civilization.

Modern industrial society. is the heir of this legacy of ecological shortsightedness. As William Rees and Mathis Wackernagel have argued in their new book, Our Ecological Footprint, the economic paradigm of industrial society. does a poor job of accounting for the earth's ecological limits; it simply does not possess the vocabulary to weigh the biological and social costs accrued by the drive for growth. Success is measured by the quantity of profit, not the quality of that profit (i.e., whether resources are squandered, workers are exploited, or natural systems are degraded). If we don't have the ability to factor these "external" costs into our economic decisions, our choices regarding consumption, population size, and technology, like those of the Hohokam, will continue to ignore the limits of the earth to support us.

First developed 20 years ago by Rees, who is the director of the University of British Columbia's School of Community and Regional Planning, the ecological footprint aims to provide this missing ecological counterpart to traditional accounting: a way to assess the biological and social costs underlying our economic decisions. For example, in British Columbia, tomato plants grown in a hydroponic hothouse are nine times more productive than their intensive field-grown counterparts, but footprint analysis by graduate student Yoshihiko Wada shows that they actually require 10 to 20 times more land, for each tomato, to supply all the materials and energy needed to run the hydroponic operation. While economically viable in conventional accounting, the hothouse tomatoes are extremely inefficient when ecological costs are considered, such as the amount of land needed to produce additional fertilizers, water, and fuel to heat the greenhouse.

On a larger scale, the footprint is able to estimate the amount of land needed annually to provide materials, energy, and waste sinks for a given...