Our Ecological Footprint: Reducing Human Impact on the Earth.

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 population (a household, city, or country). To make this possible, Rees and Wackernagel have calculated the amount of land required to provide the goods and services we consume - from the amount of farmland needed to grow a pound of coffee to the amount of forest needed to produce a newspaper.

Interestingly, when Rees and Wackernagel add up the entire human population's footprint, they find that it is 30 percent larger than the world's available amount of ecologically productive land. That is not to say that we are consuming resources that don't exist, but that we are consuming resources much faster than the earth's systems can renew them - and in some cases, we are consuming resources that will not be renewed at all. Essentially, we have dipped into the earth's principal, rather than living sustainably off the interest - and to continue this level of consumption without further depleting the future potential of ecosystems, we would need a planet 30 percent larger or more ecologically productive.

This estimation is not simply an academic exercise. In fact, the ecological fallout of our excess already has reached epidemic proportions: each year desertification encroaches on 6 million hectares of productive land, deforestation claims more than 17 million hectares, soil erosion exceeds soil formation by 26 billion tons, and an estimated 17,000 species are forced into extinction. The ozone hole has reached record size, atmospheric carbon dioxide levels have increased by 28 percent since the turn of the century, and many fisheries are near collapse. And yet, as the population continues to increase by 80 million people per year, modern industrial society remains largely unable to face up to its role in this environmental malaise.

In nature, when a patch of land is disturbed, opportunistic and aggressive weeds quickly take hold. But the use of resources by these high-growth "pioneer" communities, which are usually annuals like thistles or ragweed, is thermodynamically inefficient: life cycles are explosive and short, diversity is minimal, and energy is rapidly consumed. The "mature" ecosystems that slowly develop out of these pioneer communities, however, are geared toward long-term growth: they conserve energy, are better suited to their surroundings, and create more biomass with less resources. Pioneer communities, with their boom and bust reliance on net growth, are eventually beaten out by the more efficient and complex "mature" organisms that use available energy to cultivate growth that can be sustained.

Human history has seen numerous examples of "immature," rapid-growth civilizations that have cashed in their future stability for the sake of rapid, immediate, and often-times violent growth. The Roman empire, for example, based much of its existence on a policy of unbridled territorial expansion and conquest. Rome's expansion became self-perpetuating as the empire's stability became dependent on its ability to conquer and grow. Many of its outlying provinces were turned into granaries to supply large standing armies and the citizens of Rome with free grain. Huge amounts of topsoil were lost as provinces from North Africa to Asia Minor cut down forests and converted vulnerable hillsides to agriculture to supply increasing Roman demands. As the prospects of expansion and conquest waned, and as production from the degraded environment tapered off, the empire's moorings in unchecked growth and resource consumption contributed to internal disintegration and collapse.

Paul Hawken observes in his 1993 book, The Ecology of Commerce, that the current economic intensity of industrial nations, like the relentless expansion of the Romans, is akin to the furious growth of pioneer community weeds. Today, we have temporarily increased the human share of the earth's carrying capacity - the maximum population an ecosystem can sustain - only at great future expense; by eliminating competing species, importing locally scarce resources, consuming nonrenewable fossil fuels, and relying on unproven technological fixes. To comprehend the current scale of human consumption, it is revealing to look at Stanford University biologist Peter Vitousek's 1986 study that found the human species alone has appropriated 40 percent of the solar energy the earth receives through photosynthesis - leaving only 60 percent for the millions of other terrestrial plants and animals. If the human population doubles in the next 40 years as expected, it is doubtful that we could increase that share further without crippling many of the critical services that nature provides, such as forests' regulation of the hydrological cycle, or wetlands' filtering of pollutants. As ecological economist Herman Daly explains, "sustainable growth" is a contradiction. The earth is not increasing in size, and energy inputs from the sun remain constant, so we are limited in our ability to grow. Daly envisions "development" as a sustainable alternative to sheer growth, one that emphasizes the realization of fuller and greater potential rather than increased acquisition of resources - a transformation that mirrors the shift from pioneer to mature communities.

It is difficult to tell at what point human demands on resources and waste disposal will pass critical thresholds, but as Hawken warns, "every natural system in the world today is in decline." Our ability to temporarily exceed carrying capacity does not prove that nature has no limits, but simply that we have the ability to momentarily dodge those limits, while further degrading ecological stability for future generations. Technology and increased efficiency have been an integral part of increasing abundance in the past and will continue to be an important part of developing a sustainable future - but at current levels of consumption they can no longer be counted on to further push the limits of nature. In his 1798 essay on population, Robert Malthus observed that human population and economies are able to grow exponentially, while "subsistence," or the natural resource base that supports them, does not. While Malthus may have vastly underestimated the human potential to stretch our carrying capacity, his recognition of the earth's limits, and the fact that humans are ultimately subject to them, is prophetic.

But Malthus was not the first to observe these limits - observers in civilizations from Babylon to early China have written about the destruction of habitat and alarming increases in population. In fact, many cultures have been able to heed such warnings, and to live within nature's limits. Today, understanding and measuring those limits is one of the first steps modern industrial society must make if we plan on reducing the size of our footprints - individually and globally. Of course, a measurement alone won't change human patterns of consumption, but having a way to track ecological costs will help policymakers, the business community, and individuals begin to weigh the inherent, but often ignored, environmental costs underlying economic decisions.

Wackernagel, who studied under Rees and is now with the Center for Sustainability Studies in Veracruz, Mexico, has formulated two useful footprint applications with broad personal and policy applications since writing Our Ecological Footprint - measuring an individual's household footprint, and ranking the overall footprint of most nations. According to these studies, the average U.S. citizen appropriates 8.4 hectares of cropland, forests, pasture, built-up areas (such as buildings and roads), marine production, and land for energy to support his or her annual consumption of goods and services. The average Indian uses only 0.8 hectares. India's population may be 3.6 times as large as the United States, but the country's total ecological footprint is 3 times smaller.

Not surprisingly, footprints in affluent, developed countries are significantly larger than those in the developing world. In fact, say the authors, if the entire human population lived like the average North American, we would require at least two additional planets to live sustainability. According to footprint analysis, if all of the earth's biologically productive land were to be divided equally between humans - except for a 12 percent setaside for the earth's approximately 30 million other species - each person would get about 1.7 hectares. But as it stands, the most wealthy 20 percent of the world's population consumes 80 percent of the available resources - far beyond a fair share of 1.7 hectares. If we are exceeding global carrying capacity by 30 percent as Rees and Wackernagel estimate, the wealthy 20 percent alone occupies a footprint larger than the planet's carrying capacity, leaving no room for the less fortunate or impoverished majority to grow without further damaging nature's life-support systems.

While offering a new vocabulary for individuals and policymakers alike to weigh ecological costs, footprint analysis is not without its limitations. Like economics, the footprint is simply a model, an abstraction that is limited in its ability to accurately reflect the value of all of nature's services. The authors repeatedly emphasize that they have made "conservative" estimates of consumption (within a range of 5 percent too large and 30 percent too small), most likely to quell potential criticism of the one or two conceptual leaps the book has taken in assessing energy use. For example, they say the footprint of fossil fuel energy can be calculated in terms of the amount of land needed to sequester in trees the C[O.sub.2] produced from combustion (they estimate that every 1.8 tons of carbon emitted requires one hectare of biologically productive land annually to absorb it). Some skeptics may question the legitimacy of measuring fossil fuel footprints based on the amount of land needed to absorb the wastes they produce, since that may oversimplify the still poorly understood dynamics of carbon sequestration and global warming.

U.S. geographer George Perkins Marsh warned in his 1864 book, Man and Nature, that human impact on the earth could cause unprecedented species loss and ultimately threaten the existence of humans themselves. Since then, our population has grown from 1 billion to 5.8 billion, and our consumption of resources has increased to a level that Marsh could only have begun to imagine. But in response to this increase, a growing number of researchers like Rees and Wackernagel are providing glimpses of a sustainable alternative - charting new courses away from outlandish levels of consumption, based on honest accounting of our dependence on nature. Living sustainably, they find, will require deliberate, informed, equitable, and reduced levels of consumption.

By 600 BC, Greece was largely deforested and overgrazing had caused alarming rates of topsoil loss. Despite the Greeks' knowledge of soil-saving techniques, increased resource demands from a surging population proved too great - grazing and harvesting carried on at an unsustainable rate. Some attempts were made to halt cultivation on steep, fragile slopes, and a bounty was paid for farmers to help stabilize the soil by planting olive trees - the only tree that would grow on badly eroded land. Plato observed in his Critias. "What now remains compared with what then existed is like the skeleton of a sick man, all the fat and soft earth having wasted away, and only the bare framework of the land being left." But unlike Plato's proto-footprint observation, Rees and Wackernagel's ecological footprint offers at least a rough means of measuring our next steps toward a more sustainable level of consumption.

Curtis Runyan is assistant editor of WORLD WATCH.