Lightening the tread of population on the land: American examples

Full Text, Tables, and Figures

FOR THE PLANET to continue at least its present hospitality for Nature as people multiply in number and wealth, the human tread must lighten and narrow. Remembering that land for habitat is the preeminent need for living things and that Americans are often excoriated for heavy feet, we concentrate here on the American footprints of building, forestry, and farming.

Many of the Earth’s present 5.8 billion people look at the landscape, its waters and creatures, and hope no more hectares will be built upon, logged, or tilled. Because the number of persons has risen inexorably for centuries and most want to be wealthier, the hope of a steady environment must be realized by lightening the intensity of the tread per person and per dollar. Do American examples show promise for the world that, while people and wealth multiply, invention and changing habits can come close to holding constant the extent of paving and building, publishing and packaging, tilling and cropping? Let us search back through this century for principles, rates, and trends that may carry forward the same range of time, when Americans might number perhaps 100 million more than today and the number of all humans might be 10 billion.

The broad categories of present land use in the United States set the stage. The Food and Agriculture Organization (FAO 1994) of the United Nations classifies land use into cropland, pasture, forest, and “other”–the land not in the preceding three categories and including built-up and barren land. The US land use percentages in Table 1 can be grasped by comparing them, for example, to the 14 percent in forest and 10 percent in cropland in China, the 58 percent in forest and 7 percent in cropland in Brazil, the 68 percent in forest and 7 percent in cropland in Sweden, and the 27 percent in forest and 35 percent in cropland in France.

The spreading of the built environment

The weeds in the Roman Forum and on the Appian Way prove roofing and paving do not extinguish Nature forever–but almost. If twice as many people press onto the planet, will they cover twice as much land? The view from above the Chicago or Mexico City airport suggests at least twice.

The sprawling settlements where more and more people choose to build, commute, and engage in commerce frighten many reporters and analysts. Rationalizing the fears of land development in terms of famine comes easily to some. Periodically, news about grain supply prompts alarm. For example, “As Asia industrializes, the construction of thousands of factories, roads, parking lots, and new cities is wiping once-productive cropland off the map” (Brown 1995: 12).

In America after World War II, wealth, automobiles, and the construction of highways and “Levittowns” caused a burst of suburban land covering. By the 1970s, a national survey estimated “development” was each year covering about 1.2 million hectares, the area of the state of Connecticut (US Department of Agriculture 1990). The transformations experienced in Connecticut from farms to mill towns and then to suburbs caused by proximity to New York City make it an emblematic unit for measuring modern land development.

The amount of land covered or “developed,” of course, depends crucially on definition.1 A farmer might set the moment of the development of land early, perhaps when the perimeter of a city’s suburbs reaches his farm, while a town dweller might perceive it later, perhaps when paving and building erase photosynthesis. The US Bureau of the Census defines “Developed Land” as “A combination of urban and built-up land and roads, railroads and associated right-of-way.” By that definition, the census in 1991 reported 31 million hectares of non-Federal land developed. This total, which is 5 percent of non-Federal land in the United States, equals the territory of Poland. About 20 percent of US land is owned by the Federal government and thus not subject to typical private development. Drawing on the census and its own estimates, the US Department of Agriculture estimated that development annually during 1958-82 overtook 0.6 million hectares. Instead of a full Connecticut, Americans evidently only covered half a Connecticut in one year (Baden 1984; US Bureau of the Census 1986, 1991a; US Department of Agriculture 1990).

To understand the dynamics of covering land and bring more precision to the matter, analysts compared photographs of the same places over time and computed the frequencies of conversions among half a dozen land uses in 135 fast-growth US counties, representing 12 percent of the US population in 1970 and nearly half its increase from 1970 to 1980. The analysts found that new people were adding to urban area at nearly the same rate as the 1,000 m2 per person already living in those counties.2 In more familiar units, that is one-quarter acre, or one-tenth hectare, per person for roads, shopping centers, lawns, and dwellings.

For those who feared urbanization was eliminating cropland differentially, especially in the suburbs, the studies of fast-growth counties turned up surprises. Conversions of forest and other rural land countered cropland losses to urbanization.3 Urbanization did not consume prime agricultural land disproportionally. In the 29 fastest-growing counties, farmers shifted to more valuable products and actually sold more in constant dollars, and farmland shrank slightly less, compared with the rest of the country. As population grew in the counties, urbanization used less land per added household, unsurprising if land values rise. Our extrapolation for the indefinite future of the transitions observed among uses in the fast-growing counties suggests that less than two-thirds of their land will be eventually developed.4

Although the human tread was less than anticipated, development still spread. Ultimately it must stop. As the extrapolation just noted suggests, the limit is likely to be well below 100 percent. Present cities also hint at development’s limits. Although wedged in Manhattan’s 6,000 hectares with 1.5 million residents plus countless others during the day in its offices and shops, much of Central Park’s 340 hectares still photosynthesizes. Clearly, a limit less than 100 percent tempers a proportionality between population and development. Looking at the United States as a whole, the percentage of land set aside for public parks in 17 American cities with densities of 320 to 9,000 people per km2 ranges from 0.3 percent in Jacksonville, Florida to 19 percent in Dallas, Texas.5 Embedded in cities, the green parks let people visit Nature with little trespass on Nature.

The ratio of developed land per person varies among the 48 contiguous American states despite their similar wealth, further indicating that development does not simply track population. The tread or square meters of the land actually covered per person is less in more populous states (see Figure 1). It ranges from a high of 7,900 m2 per person in North Dakota to a low of about 400 in Rhode Island and New Jersey. Because the vast tracts of Federal land in the Rocky Mountains, Great Basin, and Pacific states are generally unavailable to private development, we eliminated Federal land by expressing the population density along the x-axis as people per km2 of non-Federal land. Measured in non-Federal land, Nevada, for example, is less than half the size of Indiana. About half of California is Federal land, leaving the area of its non-Federal land available to private development little larger than in Kansas or Nebraska and less than twice that of New York or North Carolina. On its non-Federal land, California has about the same population density as New York, and, as we shall see, the two states exhibit similar development.

In the 48 American states the covered land per capita falls from more than 2,000 m2 (about a half acre) in states where travel is fast, like Montana or Nebraska, to about 600 m2 in slower, more urban California or New York with their similar population densities. The covered land per dollar of gross state product is also less in the more populous states.

The causes and consequences of the lighter tread include crowded roads in densely settled regions. A denser population lessens the kilometers of road per person, just as it lowers the number of developed hectares per person. Slower travel shortens the practical trip and compacts the metropolis. Also, dwellers in apartments and workers in skyscrapers have small footprints on the soil. In contrast, speed spreads.

If Californians and New Yorkers used land at an average level of 2,000 m2 of developed land per person found in less densely populated states, they would claim as developed land another fifth of the non-Federal land in their states.6 The four most densely populated states would so claim another 40 to 75 percent of their uncovered land. The actual pattern of development in these populous states has thus spared a lot of land from residential, industrial, and commercial uses, and from highways and other uses included in the Census Bureau’s definition of developed land. By enduring crowding, urbanites spare land for Nature.

To grasp the scale of the land spared from development by, say, the lighter tread of Californians, who have so far developed 628 rather than 2,000 m2 each, think of the expanse spared to date as three times the area of Connecticut. Similarly, by developing at a rate of 560 m2 for each resident, New Yorkers spared twice the area of Connecticut. Californians and New Yorkers spared these multiples of Connecticut by developing fewer square meters per person than their fellow Americans in Arkansas or Iowa.

Metropolis will spread its net when transit quickens, and people will continue filling in the net. Greater wealth will enable more Americans to buy higher speed and thus cover more Connecticuts. But the example of American states depicted in Figure 1 indicates that the land covered will increase more slowly than in proportion to population.

The sparing of forests

We have written so far of people covering land for domicile, commerce, industry, and transport. They also tread on the forest, taking lumber, paper, and fuel wood–uses whose combined mass is twice that of all metals used (Wernick and Ausubel 1995). This source of products, however, exemplifies habitat for Nature. In 1992, US forests covered nearly 300 million hectares (ha), or one-third of all US land and about two-thirds of the area that was covered by forests in the year 1600.7

Most of the conversion of forest to other uses occurred in the nineteenth century. By 1920 clearing for agriculture had largely stopped. The Federal government owns about a third of all US forest land, and 6 percent of all forest land is reserved from timber harvest as parks, wilderness areas, and other places. During the past quarter-century, reservation of forest land rather than deforestation has shrunk the area classified as timberland by a few percent. Can changing consumption, recycling, and innovations in forest management and products lighten the American tread represented by logging?

Between 1904 and 1990 Americans tripled their numbers and multiplied their GNP 14-fold.8 Meanwhile total lumber production crept up by one-quarter, but paper use exploded 29-fold. These changes over 86 years can be translated into annual percentage changes, which contrast the carpenter and saw with the office worker and copier.

Relying on the identity between the national consumption of a mass of product (in tons of paper or lumber), and population, GNP per person, and product per GNP (in both cases GNP measured in constant dollars)–Product = (Population) x (GNP/Population) x (Product/GNP)–we can ferret out the determinants of total US consumption. Although the determinants multiply together to set the national consumption, their percentage changes per year add up to the change in the national consumption. In the adding and subtracting of the components of change, one can see the challenge of steadying national consumption by lightening “intensity of use,” the mass of product consumed per dollar of national economic activity.9 One can see the challenge of lessening the impact on Nature by invention and ingenuity rather than by scarcity and poverty.

Between 1904 and 1990, packaging, publication, and memos consumed more trees. Figure 2 shows the annual percentage change in US consumption of paper and lumber. The component changes in population, GNP (in constant 1982 dollars) per person, and mass of product consumed per dollar of GNP yield the average change represented by the solid bars. Expressed as an annual change, use of paper per dollar of GNP rose 0.9 percent per year. The combination of US population growing at 1.3 percent and per capita income rising 1.8 percent per year raised GNP 3.1 percent annually. Adding the 0.9 percent greater annual paper use per dollar of GNP indicates that total national paper use rose 4.0 percent annually. Lumber was a different story. Its intensity of use per dollar of GNP fell 2.8 percent per year, nearly counteracting growing population and income. The 2.8 percent fall reflects the fact that in 1990 the average American consumed about 60 percent less lumber than his counterpart in 1904.

The declining intensity of lumber use helped American forests expand. The abandonment of farmland returned relatively productive sites to forest. The control of fires, restocking, plantations, and imports helped as well. Mills lost less wood, converting former wastes into pulp for paper, composites such as plywood which Americans substituted for solid lumber, and heat and electricity; by 1980 American mills converted more than 96 percent of the wood entering their doors into useful products and energy (US Congress, Office of Technology Assessment 1984). Together, these changes caused an expansion of American forests commencing in the early 1920s. The trend continues: by 1992 the inventory of growing stock in US forests was 27 percent larger than in 1952, the first year of comprehensive data collection (Sedjo 1991; Smith, Faulkner, and Powell 1994).

The ultimate goal of a lighter tread lies beyond saving paper cups and wooden pallets. The goal, sparing Nature, brings into consideration the recycled paper and residue from sawmills that are fed into the manufacture of paper. Residues from sawmills now supply more than one-third of the pulpwood used in the manufacture of paper. Driven by the costs of disposing of the full one-third of US municipal solid waste that currently is paper, recycling burgeons. It may soon contribute half the raw material for paper, an amount that would replace 10 to 15 percent of the current annual harvest of wood.10 Recycling reaches limits because the manufacture of paper always costs the pulp some of its needed fiber and because less harvest would lower stumpage prices and thus favor use of lumber. The inevitable losses during recycling and other costs make a lower intensity of use of paper a greater potential means of sparing trees.

We can translate the harvest of fewer trees into forest area saved, the saving of diverse habitats. The simplest translation uses the ratio of all timber standing to the area of American forest land. We express the spared expanse as multiples of the area of an exemplar of Nature, Yellowstone National Park, the first national park created in the United States. Using the ratio of standing timber to land, the 15 percent harvest spared by making half of American paper from recycled paper spares about 900,000 hectares, the area of Yellowstone, every year.11

A further route to sparing Nature lies in foresters raising yields so that less habitat is disturbed by harvesting the wood demanded. For example, one-quarter of American forest land could grow an average of 6 to 8 m3 per hectare annually, or two to three times the present average annual growth. Harvesting only this potential annual growth on one-quarter of the forest land–not clear cutting the forest–would yield somewhat more than the annual removals from all American forests today and would demonstrate how foresters could spare habitat.12 Tree farms in warm places annually yielding 5 to 90 m3 per hectare (Carpentieri, Larson, and Woods 1993) could shrink the harvested area even more, and the promise of genetic engineering beckons ahead (Moffat 1996).

The sparing of cropland

US farmers use an expanse for growing crops far wider than urban development and nearly as wide as forests. After rising about a quarter from 1900 to the 1920s, US cropland has remained steady. While population grew by nearly one-fifth from 1975 to 1992, US cropland and pasture shrank by one percent. Like the forest, cropland yields products–food, feed, fiber, and flavoring.

Animal feed (corn, oats, barley, and sorghum) is grown on one-third of US cropland. The diet of consumers, their numbers, the efficiency of converting feed to meat, and the yield grown per hectare affect this expanse of cropland. Analyzing the components of change in the amount of cropland used to raise feed crops shows how a diet of meat affects the use of cropland area. Much meat, largely beef, comes from grazing rather than from feed crops, and to neglect grazing exaggerates the impact of beef consumption on cropland use and ignores its impact on pasture or range. By assuming that all meat comes from feed, however, we can calculate roughly how much the changing components of meat consumption and yield have lightened the tread on cropland and so countered the rising numbers and wealth of Americans.13 Because meat typifies the diet of the rich and beans that of the poor, growing wealth and growing populations elsewhere lend special importance to this American example.

As with the example of paper and lumber, in Figure 3 the components of change in US cropland used to raise feed crops yield the average annual change represented by the solid bar. The first three components of change in national use of land for feed are the annual changes in population, GNP, and intensity of use–in this case the quantity of meat per dollar of GNP. The components of change in Figure 3, however, must be extended to reach land use.

Annually on average from 1967 to 1992, US population rose 1.0 percent, and GNP per person 1.5 percent, lifting GNP growth to just over 2.5 percent. But, surprising environmentalists and cattlemen alike, consumers lowered their annual meat consumption per dollar of GNP by 1.5 percent. Americans held average consumption per person steady by lowering their consumption per GNP as fast as they grew wealthier.

At the same time, Americans changed the mix of meats they ate, consuming somewhat more poultry, about the same amount of pork, and less beef. Because poultry convert feed to meat efficiently and because we assumed all beef is produced from grain, the calculated feed to produce a unit of meat fell at an annual rate of 0.9 percent. The declining amount of meat consumed per dollar and the declining mass of feed used to produce a unit of meat measure how much consumers lightened their tread.

Also, farmers raised yields of feed grain, lessening the area of land used per unit of feed produced by 2.4 percent annually. They did not tarnish this achievement by using more and more energy, pesticides, or fertilizer, or by eroding soil. For over a decade American farmers have lowered their consumption of energy and held steady the total quantity of organic pesticides and fertilizer. They have lessened erosion.14

When the lightening of steps wrought by consumers and those by farmers are summed, they outweigh the multiplication of people and their incomes. The cropland calculated for grain-fed animals to produce meat for Americans shrank 2.2 percent annually. (Other calculations that allow for grazing temper this estimated shrinkage.) The 2.2 percent annual shrinkage adds up to 21 million hectares between 1967 and 1992, or one and a half times the area of the agricultural state of Iowa or 24 Yellowstones.15


Sparing Nature challenges people to lighten their individual tread as fast as or even faster than population and wealth multiply. The American experience in meeting this challenge offers enough hope that fear about our impact on land and natural habitat need not transfix us–or the Chinese (Smil 1995).

If during coming decades 100 million more people arrive on American land, how much land will they cover? In several less-populous states today, development covers more than 2,000 m2 per person. Urbanization, however, seems destined to pack the 100 million into the more populous states. A more logical scenario than 2,000 m2 of development per person, therefore, envisions the new arrivals developing land nearer the present lighter rate of 600 m2 in populous California and New York rather than at 2,000 m2. Indeed, history hints that, while development will spread at a rate modified by wealth and the speed of travel, it will not crush the countryside and Nature in a simple proportionality with population. One hundred million people developing land at 600 m2 each would consume 6 million hectares or 7 Yellowstones. Nevertheless, the difference between 600 and 2,000 m2 would spare 14 million hectares or 16 Yellowstones.

Should the new arrivals raise the number of Americans to 350 million and should all of them cause the same per capita removal of wood from timberland as in 1991, removal would then exceed the present net growth of timberland.16 Although the tempered use of lumber brightens hope for no greater impact on Nature, the limited effect recycling can have on harvest and the expected rises in the use of paper dim the hope. Thus the burden for sparing forest habitat rests heavily on foresters raising the yield per hectare. The excess of potential above actual production on forest land and experiments with tree clones show that the foresters’ task of sparing land is achievable. At the modest goal of annual net growth raised to 4 m3 per hectare, the wood to be removed to satisfy the needs of 350 million Americans at the 1991 per capita rate could be grown on 82 percent of the present expanse of 198 million ha of timberland. The 18 percent of present timberland that could be thus protected equals 40 Yellowstones.17

During the past two generations, Americans cut cropland use per person in half while doubling their numbers and multiplying their GNP eightfold. They also exported much food and ate better. If American farmers accommodate the next 100 million people by raising yields rather than expanding cropland, they will lighten the human tread enough to spare more than 70 Yellowstones.18

The weight of the tread modifies the impact of population on the environment. While humanity grows richer and multiplies toward 10 billion, it has work to do, reserving diverse Central Parks and shaping sprawling settlements, taming the copiers in offices, lifting timber yields, and continuing to raise crop yields. Past American successes in sparing Nature through invention, innovation, and changing habits rather than the negative checks of scarcity and poverty encourage this work. Its benefit may exceed 100 Yellowstones, equivalent to one Nigeria or one Bolivia.


An earlier version of this article was prepared for the Annual Meeting of the American Association for the Advancement of Science, Baltimore, 9 February 1996.


1. The uncertainty of estimating developed land can be read clearly on pp. 18-21 of US Department of Agriculture (1990), and the base amount to which the 1.2 million ha of the earlier appraisal was presumably added is uncertain. The US Bureau of the Census (1986) definition reads: “Urban and built-up land areas cover land used for residences, industrial sites, commercial sites, construction sites, railroad yards, small parks of less than 10 acres within urban and built-up areas, cemeteries, airports, golf courses, sanitary land fills, sewage-treatment plants, water-control structures and spillways, shooting ranges, and so forth. Rural transportation is land used for roads and railroads in rural areas.” Publication of the developed area is a fairly new feature of census reports; in 1991 the Census Bureau combined urban, built-up, and rural transportation in the single class of developed land.

2. Vesterby, Heimlich, and Krupa (1994: 44) calculated conversion of land per household. When calculated per person, their rates of conversion from 1960 to 1980 ranged from 600 to 900 m2. Whether calculated per person or per household, the rates of conversion were less than, say, the inventory of 900 to 1100 m2 of urban land per person established by all the earlier settlement of the counties. The authors wrote, “Both U.S. population and the amount of urban land increased in the 1960s and 1970s, but the marginal rate of urban land conversion per household remained constant.”

3. In terms of Table 1, the conversion of cropland (the top category) to urban (in the bottom or “other” category) was countered by conversions from the range and forest segments. From 1970 to 1980 in the fast-growth counties, some 5.6 percent of cropland and pasture was reportedly transformed, 0.5 percent to forest, 1.4 percent to range, and 3.7 percent to urban. In the same counties, gains of 1.0 percent from forest and 3.1 percent from range countered the loss of cropland and pasture.

4. Regarding prime land, gains from forest and other rural land, and urbanization per household see pp. 36, 40, and 48 of Vesterby, Heimlich, and Krupa (1994). About selling more and shrinking less land see p. 107 of Vesterby and Krupa (1993). Extrapolating the transitions among uses in the fast-growing counties in the United States as a stationary Markov chain gives a steady state of two-thirds of the land urbanized after several centuries. The state of the land is extrapolated by multiplying the matrix of transitions among the land use categories by itself. Underlying the extrapolation are two assumptions: (1) that the probabilities of conversions or transitions from one category to another are constant; and (2) that the probabilities depend not upon how land enters a category but only upon the class it is in. Because events will inevitably change the transition probabilities estimated from only a decade or two of experience, the outcome of the calculation is only an orderly extrapolation of recent experience.

5. The cities are Atlanta, Baltimore, Boston, Cincinnati, Dallas, Jacksonville, Kansas City (Missouri), Los Angeles, New Orleans, New York, Omaha, Philadelphia, Phoenix, St. Louis, San Jose, Seattle, and Washington, D.C. The low of 0.3 percent is in Jacksonville’s 600 ha and the high is attained by the 19,000 ha of public parks in Dallas. Six of the 17 cities have more than 10 percent of their land in public parks. The park areas were transcribed from pp. 754 et seq. of Information Please Almanac (1989).

6. For example, the 30 million Californians average 628 m2 of developed land each. At 2,000 each, i.e., 1,372 m2 more, they would have developed another 4 million hectares, which is about one-fifth of the 22 million hectares of non-Federal land in California.

7. Smith, Faulkner, and Powell (1994) provide a full glossary and data for US forests. For example, forest land is at least 10 percent stocked by trees, including formerly forested land where trees will be regenerated. About two-thirds of forest land is timberland, which is not reserved and is capable of producing more than 1.4 m3 per ha per year. Sedjo (1991) gives information about trends.

8. Sources for population, GNP, and quantities of forest products are US Bureau of the Census (1991b) and US Department of Agriculture (1993a) and other volumes. GNP was measured in 1982 dollars. For the initial year of our series we chose 1904, the first year with a report of all components of paper and board production, imports, apparent consumption, and waste paper consumption. We call the pulp products of paper and board simply “paper.”

9. As Wernick et al. (1996) illustrate, “intensity of use” is a core concern of industrial ecology.

10. If a ton of pulp equals 2 m3 of wood, a flow chart of wood products in 1993 (Ince 1994a) indicates 258 million m3 entering pulp and paper manufacturing. Increasing the present 53 million m3 recycled to half the input of 258 (or 129 million m3) would save 76 million m3, which equals 15 percent of the harvest of 501 million m3. An economic model that incorporates the impact of saving on price and lumber consumption projects a saving of only 10 percent (Ince 1994b).

11. The yield per land determines how much habitat will be spared by saving 76 million m3 by recycling. A simple estimate of yield is the ratio of the 24,269 million m3 of all timber standing on all 298 million hectares of US forest land (Smith, Faulkner, and Powell 1994). At that rate, not harvesting 76 million m3 annually spares 0.9 million hectares, the area of Yellowstone Park. Another conversion of wood saved into area spared uses the increment of growth rather than the inventory of standing trees. The two-thirds of US forest land called timberland is producing or is capable of producing crops of industrial wood and is not set aside by the government. The average annual growth on this timberland is 3.1 m3 per hectare. At that rate, not harvesting 76 million m3 spares the annual growth on 24.6 million hectares or 25 Yellowstones.

12. Foresters judge that the 67 million hectares of US forest land capable of growing 6 to 8 m3 of wood per hectare annually could produce 515 million m3 in all. The 67 million hectares are 23 percent of forest land. In 1992, 462 million m3 of wood were removed (Smith, Faulkner, and Powell 1994).

13. Waggoner (1996) calculated the use and production of meat, feed, and grain. He calculated the quantity of meat from the slaughter of beef and swine and the average weights of their carcasses as reported by FAO in its annual production yearbooks and by the US Department of Agriculture (1993b). Because reports of poultry meat in the United States in the latter reference began in 1967, he chose 1967 as the initial year. The ratio of feed to meat was assumed to be 12, 6, and 3 for beef, swine, and poultry; this is consistent with values reported by the US Department of Agriculture (1993a). By converting meat into grain equivalents and so neglecting grazing by cattle, we magnify the effect on cropland of changes in beef consumption. See Council for Agricultural Science and Technology (1980) for proportions of grazing versus feed grains for production of meat. Finally, land per feed was calculated from the yield of coarse grain reported by the US Department of Agriculture (1993b).

14. Rising yields and opportunity for more are described by Waggoner (1994). Between its maximum (in 1977) and 1991, total energy use in agriculture fell by 30 percent, while use per output of agricultural product fell by 45 percent (US Department of Agriculture 1994). The steady quantity of organic pesticides can be read in Table 367 of US Bureau of the Census (1991b). FAO reports fertilizer consumption in its annual yearbooks. Keeney and DeLuca (1993) showed that nitrate concentration in Iowa’s Des Moines River was about the same in 1945, 1955, and 1976 as in 1980-90. The 1992 National Inventory shows that from 1982 to 1992 annual sheet and rill erosion per cultivated acre in Iowa declined by 28 percent and in Kentucky by 31 percent; in the entire nation during the decade, water plus wind erosion declined by one-third (US Department of Agriculture 1995).

15. The cropland calculated for feed fell from 50 to 29 million hectares between 1967 and 1992; this decline (21 million ha) is 1.5 times the 14.6 million ha of Iowa and 23.8 times the 0.9 million ha of Yellowstone. Because we calculated meat consumption from slaughter, assumed constant meat-to-feed ratios, and neglected grazing, our results need the test of comparison with other reports. Although the absolute quantity of meat consumed differed between our calculations and the reports of the US Department of Agriculture (1993b), the relative rise of poultry and decline of beef are similar. Further, the number of cattle in the United States has fallen by one-quarter since its peak in 1975. Our calculated 1.5 percent annual decline in meat per dollar of GNP agrees with the change reported by the US Department of Agriculture. The 0.9 percent annual decline we calculated for meat per feed, however, does not agree with the Department’s report of a 0.1 percent rise for concentrates fed to animals per unit of meat produced. Our neglect of grazing likely caused this disagreement. As beef consumption lessened, the contribution of grazing declined, countering the theoretical improvement in the meat-to-feed ratio in our calculation. This in turn lessened the shrinkage of cropland to produce meat from our calculation of 2.2 percent to 1.2 percent per year. Our calculation of 2.2 shows the impact on cropland envisioned when feed ratios are quoted; the calculation of 1.2 indicates the impact when grazing played a real role.

16. Smith, Faulkner, and Powell (1994) report that in 1992 the area qualifying as timberland was 198 million hectares out of the 298 million hectares of forest land in the United States. They also reported that on the timberland in 1991 net growth was 612 million m3 and removals 462. At the present annual per capita removal of 462/250 or 1.9 m3, 350 million people would remove 647 million m3, exceeding the net growth of 612 million m3.

17. We calculated use [(Future population) / (Present) x (Million m3 present removals)] or [350/250 x 462] = 647 million m3. At 4 m3 per hectare net growth, the 647 million mcould be grown on 162 million hectares, 82 percent of the present 198 million hectares of timberland. The difference between 198 and 162 million hectares is 40 times the area of Yellowstone Park.

18. In 1992 cropland in the United States was 0.63 hectares per capita. At that rate, 100 million more people would require 63 million additional hectares for raising crops. Conversely, assuming the rise in population, a static American diet, and an annual one percent rise in the average crop yield in the United States over the next century, the land spared from raising crops would be equal to over four times the area of Iowa and 70 times the area of Yellowstone Park. Note that this sparing is from all crops, not just feed, and that grazing complicates its calculation little.


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——. 1995. Summary Report. 1992 National Resources Inventory (Revised). USDA Natural Resources Conservation Service. Washington, D.C.

Vesterby, Marlow and Kenneth S. Krupa. 1993. “Effects of urban land conversion on agriculture,” in Eric M. Thunberg and John E. Reynolds (eds.), Urbanization and Development Effects on the Use of Natural Resources. Southern Rural Development Center Publication 169. Gainesville: University of Florida, pp. 85-114.

Vesterby, Marlow, Ralph E. Heimlich, and Kenneth S. Krupa. 1994. Urbanization of Rural Land in the United States. Agricultural Economics Report 673. Washington, D.C.

Waggoner, Paul E. 1994. How Much Land Can Ten Billion People Spare for Nature? Report 121. Ames: Council for Agricultural Science and Technology.

——. 1996. “How much more land can American farmers spare?” in Burton C. English, R. White, and Liu-Hsiung Chuang (eds.), RCA III Symposium on Crop and Livestock Technologies: Proceedings. Washington, D.C.: US Department of Agriculture.

Wernick, Iddo K. and Jesse H. Ausubel. 1995. “National materials flows and the environment,” Annual Review of Energy and Environment 20: 462-492.

Wernick, Iddo K., Robert Herman, Shekhar S. Govind, and Jesse H. Ausubel. 1996. “Materialization and dematerialization: Measures and trends,” Daedalus 125, no. 3: 171-198.

Materialization and Dematerialization: Measures and Trends


“Revenge theory” postulates that the world we have created eventually gets even with us, twisting our cleverness against us.1 Helmets and other protective gear have made American football more dangerous than its bare predecessor, rugby. Widened roads invite more vehicles, which mitigate gains in average traffic speed and flow. In short, human societies face unintended and often ironic consequences of their own mechanical, chemical, medical, social, and financial ingenuity.

In 1988 Robert Herman, Siamak Ardekani, and Jesse Ausubel began to explore the question of whether the “dematerialization” of human societies is under way.2 At that time, dematerialization was defined primarily as the decline over time in the weight of materials used in industrial end products or in the “embedded energy” of the products. More broadly, dematerialization refers to the absolute or relative reduction in the quantity of materials required to serve economic functions.

Dematerialization matters enormously for the human environment. Lower materials intensity of the economy could reduce the amount of garbage produced, limit human exposures to hazardous materials, and conserve landscapes. From time to time, fears arise that humanity will imminently exhaust both its material and energy resources. Historically, such fears have proven exaggerated for the so-called nonrenewable resources such as metals and oil. Yet if the human economy were to carelessly metabolize large amounts of Earth’s carbon or cadmium, the health and environmental consequences could be dire. Meanwhile, the so-called renewable resources, such as tropical woods, are proving difficult to renew when demand is high. Thus, a general trajectory of dematerialization would certainly favor sustaining the human economy over the long term.

Is dematerialization occurring? Certain products, such as personal computers and beverage cans, have become smaller and lighter over the years. However, revenge effects may still countervail. A vexing case is that total paper consumption has soared despite claims that the electronic information revolution would create a paperless office. Americans now use about a kilogram of paper per day on average, twice the amount used in 1950.

In this essay we report further analyses of materialization and dematerialization, mostly for the United States during this century, and lay the basis for a systemwide assessment. We segment our analysis to consider measurements: 1) at the stage of resource extraction and the use of primary materials, such as minerals, metals, and wood; 2) in industry and industrial products; 3) at the level of the consumer and consumer behavior; and 4) in terms of the waste generated. At each stage one can ask whether dematerialization is taking place, what drives it, and what are its future trajectories and their consequences. Our studies consider materials in absolute terms, per unit of economic activity (measured by means of gross national product, GNP, or its slight “domestic” variant, GDP), and per capita. We assess changes in both volume and weight.

Materials consumption is analytically less tractable than energy use. It cannot be satisfactorily reduced to single elementary indicators such as kilowatt-hours or British thermal units. To illustrate this point, a pound of gold cannot be simply compared with a pound of lead, to the frustration of the alchemists. And neither one can be easily compared with a pound of plutonium. Materials possess unique properties, and those properties provide value, define use, and have environmental consequences. To capture these and other interactions, we must consider an ensemble of measures under the rubric of dematerialization.

The pattern of materialization and dematerialization, and the database from which it is drawn, helps frame the new field of industrial ecology.3 Industrial ecology is the study of the totality of the relationships between different industrial activities, their products, and the environment. It is intended to identify ways to optimize the network of all industrial processes as they interact and live off each other, in the sense of a direct use of each other’s material and energy wastes and products as well as economic synergism. The macroscopic picture of materialization can help raise key research questions and set priorities among the numerous studies of materials flows and networks that might be undertaken. It puts these in a dynamic context of both technical and market change.

Dematarialization and Primary Materials

In analyzing primary materials, it is helpful to begin with a profile of the total “basket of stuff” that a human society consumes. For this purpose, let us consider first “demandite,” an imaginary, composite material representative of the nonrenewable resources we use. Demandite reveals our elemental preferences. All the materials that make up demandite are quantified in terms of the total moles of each element (or selected compounds) they contain; demandite is characterized by the fraction of moles for each element or compound divided by the total mole number. First proposed by Goeller and Weinberg,4 demandite includes both the energy materials (the hydrocarbon fossil fuels: coal, oil, and gas) and other materials, such as iron, copper, sulfur, and phosphorus, that are mined and used in the production of goods. Demandite omits some (crushed) stone that is used to build roads and other structures; the amount mobilized is quite large (about 1 billion metric tons in the United States in 1990) but this stone resource is practically infinite, and its elemental composition is more or less the average of the Earth’s crust. Following Goeller and Weinberg, we recalculated the percentage of moles of the composite materials in demandite for the United States for 1968 and estimated these percentages for 1990 (see Table 1).5 Table 1. Demandite (United States).

The hydrocarbon compounds dominate demandite. They swelled from about 83 percent of US demandite in 1968 to over 86 percent in 1990. In fact, total US consumption of hydrocarbons in 1990 was over 1.9 billion metric tons (t) or about 7.8 t per capita (20 kg per capita per day). The extraction and use of hydrocarbons pose problems such as global warming and oil spills, as well as health threats from urban, vehicular, and groundwater pollution.

The carbon, not the hydrogen, of course, is the “bad” element in the environmental story. The “decarbonization” of the economy is thus clearly of paramount environmental importance. As discussed by Nakicenovic,6 relative to GNP and energy production, decarbonization is occurring steadily. Yet absolute carbon consumption by weight in the United States grew at a compound rate of 1.8 percent per year between 1950 and 1993.

Excluding energy materials, US material flows, including crushed stone and all other physical materials as well as renewables (with the exception of food), amounted to about 2.5 billion metric tons in 1990 or about 10 t per person (28 kg per capita per day).7 Construction materials dominated with 70 percent of total apparent US consumption (see Table 2). Materials in this category may be associated with local environmental issues as excavations and structures transform the landscape, for better or worse. A striking fact is that 30 percent of the industrial minerals consumed dissipated into the environment and thus were rendered practically unrecoverable.

Table 2. Non-Fuel Materials Flows (United States, 1990).

Fluctuations but no trend in absolute consumption by weight of physical materials are evident for the United States for the past twenty-five years.8 However, an assessment of consumption per unit of economic activity shows a dematerialization in physical materials of about one-third since 1970. The oil shocks of 1973 and 1979 appear to have ratcheted the ratio down.

Table 3. Material Densities in Metric Tons/Cubic Meter.

A complete current accounting of materials consumption in America, including renewables, nonrenewables, and both energy and nonenergy materials, reveals a total of more than 50 kg per capita per day.9 (We have excluded the consumption of water and air.) This equals about 20 t/yr. If we assume a constant consumption over eighty years, an individual American’s lifetime consumption would be 1,600 t. If the average material has the density of water (see Table 3), the volume of material consumed in one person’s lifetime would be equivalent to a cube measuring about 13 meters on a side.

Disaggregation reveals that the intensity of use of diverse materials has changed dramatically over the twentieth century (see Figure 1).10 In terms of the weight of material used, normalized by GDP, timber sloped steadily down from its top position in 1900. Steel, copper, and lead also slid from their earlier heights. Plastics and aluminum followed upward trajectories, as did phosphates and potash, key ingredients in agricultural fertilizers.

Wood remained the preeminent material in the United States into the 1930s. It was used for fuel and as the structural material to build homes, workshops, vehicles, and bridges. It provided both ties and rolling stock for railroads as well as lamp, electric, and telephone poles for the utility infrastructures. Wood was gradually replaced by other materials and made more durable by creosote and other preservatives. Since 1930, annual US per capita consumption of commercial lumber has remained stable at about 200 board feet, down from about 500 board feet per capita at the turn of the century. An 80-foot spruce measuring 15 inches in diameter at breast height typically yields 200 board feet and is about sixty years old. The wood pile in earlier times was much larger, of course, because of the noncommercial use of wood for fuel.

In 1900, less than 2 percent of the timber cut in the United States produced pulp and paper. Today that fraction is over 25 percent. Absolute paper consumption has climbed steeply (see Figure 2), while consumption per capita has risen more slowly. Amidst the electronic revolution, paper remains a preferred carrier of information. New technologies for information storage supplement the range and augment the amount of information stored, rather than reduce the use of paper. But, as Figure 2 also shows, paper consumption per unit of GNP has stayed essentially flat since 1930. During World War II, America briefly and drastically reduced its paper use relative to GNP or, rather, increased GNP without increasing its paper use.

Newly exploited materials now complement traditional ones, fortifying and enhancing their properties like vitamins. Materials such as gallium, the platinum-based group, vanadium, and beryllium have come into use in electronics and in the production of steel alloys and other “designer materials.” The absolute amounts are small (10-4-10-2 kg per capita per year) and relatively steady.11 The small amounts of these new materials understate their importance both economically and environmentally. Extensive processing before final use may involve large ore bodies and mine wastes. Near optimal use is then made of the elemental physical and chemical properties of the refined materials. Precisely because of their potency, these are distributed in small amounts that are sometimes difficult to recover, thereby frustrating efforts to recycle other materials “contaminated” by them.

Although the weight of materials employed may be stable or declining, the volume of materials is gradually increasing in the United States. Average density values (Table 3) can be combined with consumption data for individual materials to estimate the total volume of materials consumed. As shown in Figure 3, since 1970 volume per capita of the combination of paper, wood, metals, and plastics has increased along with economic growth, according to a linear best fit of the data and notwithstanding the oil price shocks of 1973 and 1979. Within five years of each shock, the system had resumed its long-term volumetric expansion. Individual items in the American economy may be getting lighter, but the economy as a whole is physically expanding.

Plastics, as a result of their increased consumption, account for much of the growth in volume; they are the preferred lower density materials. Polymer plastics are a “manufacturer friendly” material because they can be shaped into complex geometric forms with relative ease, are chemically inert, and can be created with a wide range of properties. Plastics have occupied market niches from car bumpers to soft-drink containers to furniture and plumbing parts.

Although commercial plastics were introduced early in the century (Bakelite, in 1909), they did not seriously enter the economy until 1940. About 500 billion kilograms of plastic have been produced so far in the United States, or, in terms of the current US population, about 2,000 kg per capita.12 Extrapolating the historical production, we estimate that the cumulative amount of plastic resin produced in the United States will roughly double by 2030. The primary feedstocks for plastic are oil, the dominant hydrocarbon, and, more recently, natural gas. One might say that plastics have been a by-product of the automobile. As long as cars run on oil, new plastic resin will be cheaply available. However, the decarbonization of the energy system and the growth of the plastic endowment will encourage much greater recycling of plastics over the next three or four decades, countering the mounting problem of plastic waste disposal. The high level of customization of plastics complicates matters, as this diversity makes effective separation and reuse more difficult.

Dematerialization in Industry and Industrial Products

We can readily assess two relevant aspects of the materials used in industry: the dematerialization of individual end products and the use of recycled materials in production. More complete “life-cycle analyses” of products must embrace such partial examinations and extend them. For example, knowing the complete material and energy demand of a typical milk container throughout this century would be revealing. At present, we are unaware of life- cycle analyses repeated over time that provide an indication of trends.

Several individual end products manifest dematerialization. Containers, for example, have generally become lighter. At mid-century, beverage containers were predominately made of steel or glass.13 In 1953 the first steel soft-drink can was marketed. The public accepted it, resulting in the erosion of the market share of the heavier glass containers. Cans of aluminum, a material one-third the density of steel, entered the scene a decade later and grew from a 2 percent market share in 1964 to almost 90 percent of the soft-drink market and about 97 percent of the beer market by 1986. The aluminum can was itself lightened by 25 percent between 1973 and 1992.14 In 1976, polyethylene terephthalate (PET) resins began to occupy a significant portion of the market, especially for large containers, where glass had previously dominated.

Cars have also become lighter on average, although the recent sales growth of light trucks and sport vehicles counters this trend. The car is an interesting object for study because it represents a full market basket of the products of an industrialized economy, including metals, plastics, electronic materials, rubber, and glass. Cars have become more materially complex as well, an important factor in the difficulty of disassembly and reuse. Only recently have legislative and engineering efforts, particularly in Germany, been directed toward the design and eventual production of car components that can be replaced and recycled with minimal effort. In the early 1970s, the amount of carbon steel in the average US car began to decline and then fell sharply by about 300 kg or 35 percent (see Figure 4). A combined increase of about 100 kg in plastics and composites and in high-strength steel helped “downmass” the automobile while maintaining its structural integrity, with the new materials substituting for the old in a ratio of about one to three.

Although aircraft use a tiny fraction of all materials, the aerospace sector, where performance demands are exceptionally stringent, has foreshadowed trends that later appear in the rest of the economy. The drive to downmass aircraft while improving their performance has placed the aerospace industry at the forefront of materials research. Each kilo safely shaved in design saves both fuel and money. The aerospace industry provides the strongest market for composite materials of carbonaceous fibers mixed with aluminum and titanium, which have excellent strength-to-weight ratios. Materials with greater thermal resistance also yield higher performance. An increase of 80°C in the operating temperature of a jet engine can yield a 20 percent increase in engine thrust.15 Engines once formed from pure nickel now include nickel and cobalt-based superalloys, aluminum-lithium alloys, and ceramics, all having superior thermal properties. Specialized coatings and paints used on aircraft now provide significant environmental handling challenges. The mounting trend here is toward complexity, not only in the final product, but in the processing stage as well as ultimately in disposal.

The closure of materials loops through the reuse of materials complements the downsizing route to dematerialization. While smaller and lighter products can reduce the amount of materials required by future generations to operate the economy, reuse and recycling can also minimize fresh inputs and waste outputs.16 At present, secondary inputs to production have difficulty competing with virgin materials in many markets.

Successful secondary materials recovery relies on two basic factors: ease of isolation of the desired materials and consumer demand for reprocessed materials. The difficulty of isolation explains why only 7 percent of cadmium-loaded waste was recycled from hazardous waste streams in 198617 and an even smaller fraction of arsenic and thallium. The ease of isolation explains why lead now enjoys a recovery rate exceeding 70 percent of its demand. Lead is used mainly for automobile batteries, which are readily separated from the general waste stream. Dissipative uses of lead (e.g., paint and gasoline) have been substantially curtailed over the last few decades. The supply of wastepaper, also easily separated, has proved responsive to market demand, with a growing number of paper mills now accepting this source of fiber.

Steel is another material that is readily separated. The secondary supply neatly meets the demand created in large part by the technology of electric arc steel production, which relies primarily on scrap inputs. Electric arc steel production has risen steadily throughout the century and now constitutes about 40 percent of all steel production. Trace contaminants in scrap piles may confound future gains in this method of steel production, however. Contaminants, such as zinc, can be problematic even at a level of tens of parts per million and can result in substandard finished steel.

Demand for secondary materials, like all demand, is to a large degree a function of price. Precious metals such as gold and silver are commonly recovered from circuit boards. However, even the recovery of precious metals has limits. In the late 1980s, platinum prices needed to exceed $500 an ounce to make platinum recovery from catalytic converters economical.18 Energy prices can spark secondary materials recovery trends in opposite directions. Recycled aluminum requires only 5 to 10 percent of the energy necessary for primary production, and this difference has spurred secondary recovery when energy is costly. At the same time, cheap and plentiful energy is often the obvious technical requirement for economical reversal of the dissipation of many materials, even when diluted to concentrations found in sea water.

The fraction of the total production of given materials supplied by secondary materials recovery broadly indicates the extent to which the economy functions with closed materials cycles (Figure 5). This measure shows little change for paper and zinc since early in the century. Copper rose rapidly in the early part of the century but has not been able to sustain an upward trend since 1940. Aluminum jumped in the late 1970s but may have plateaued again. Steel has climbed and points toward 50 percent. As noted, lead has surpassed 70 percent. World War II elicited peaks of materials reuse in the United States for several materials. These levels of reliance on recovered materials, often about 40 percent, may represent the current practical upper limit for many materials. The reasons appear to be not so much physical as economic. For example, suppliers of virgin materials can adjust their prices to undercut recycled supplies. Economic and population growth, of course, tend to draw new materials into the system.

Dematerialization and Consumers

The number of consumers and their individual and collective behaviors drive materialization. An obvious fact is that there are more and more consumers. During the twentieth century the population of the United States has more than tripled, from about 80 million to more than 250 million. The absolute number is only part of the story. Life-styles also shape demand. Today, only a small fraction of consumption in wealthy nations (or communities) is actually for basic survival; most is for pleasure and to express one’s standing in society.

Although fast modes of travel have enabled settlements to spread, Americans on average appear to be increasing the density of their built environment over time. An analysis of data from many diverse neighborhoods in Austin, Texas, indicates that the average size of a residential plot decreased between 1945 and 1985 (Figure 6). Meanwhile, the average floor area of an Austin residence increased by 50 percent or more. The fraction of a plot covered with a structure also increased by about 50 percent in both the mean and the aggregate.

A steady increase in land value over the years could contribute to the decline in plot area in some zones. “Market forces” may adjust the size of the plot area to reduce the impact of higher costs of land. In any new development, most of the land parcels are not portioned off by prospective buyers but rather by the developers. Hence, apart from making a binary decision whether or not to purchase, the buyer has limited influence on the subdivision planning and design process. The process of fixing the size of plots may be driven primarily by the economics of the situation as perceived by the developer.

Our hankering for a domicile in idyllic settings was what drove us to suburbia. Contrary to conventional belief, once we get there, we do not seem to care about how small the plot area is. Notwithstanding professed tastes for open space, we seem to build, enclose, and accrete steadily. We also seem to display a preference for larger and larger floor areas. This would also suggest that we have enough money to spend on larger houses or the material goods to fill up all the new (or “extra”) floor area, but we are not perceived as having the desire to spend on larger plot areas.

Today’s enlarged homes house fewer people. The number of residents per housing unit has declined monotonically in the United States from five in 1890 to fewer than three today (Figure 7). Interestingly, when the increase in floor area over time is viewed in conjunction with the decrease in the average number of residents per occupied housing unit, one could conclude that the floor area available per person almost doubled in forty-five years. This hypothesis should be treated with caution because it combines national aggregate data with data only for the city of Austin.

The trend toward larger floor areas housing fewer people implies that our consumption of building materials on a per capita basis is increasing, as is our requirement for energy services such as heating and cooling.19

National data on the weight of household moves corroborates the Austin data of an increase in floor area. Data on the weight of household goods transferred in intercity moves implies that Americans on average possess more stuff over time. The average load increased by almost 20 percent to 3,050 kg (about a sixty-day stock of accumulated materials at the American rate of 50 kg/day) from 1977 to 1991.20 Intercity freight transport, measured in ton-miles, also aggregates a great deal of material. This measure indicates that as time goes by, Americans either ship more tons, ship each ton farther, or both. In 1990 Americans on average shipped freight 11,000 ton-miles; this compares with about 7,200 ton-miles in 1950. An increase in the weight, and therefore very likely the bulk, of possessions moved implies a need for more household space. Conversely, an increase in household floor space would always be filled by our insatiable appetite for possessions.

We also ship more information. The number of pieces of mail per capita in the United States has more than tripled since 1940 and stands today at more than 650 pieces per capita annually. Conservative estimates of the growth rate of electronic mail transmission and use in the United States is a phenomenal 10 percent per month. The information economy does not appear to substitute for the materials economy but may rather be required to manage its growth.

Whatever the reasons, from the vantage point of building materials, structures, and household amenities per capita, wealth appears to be a materializer. The shift from larger to smaller families materializes. Each housing unit is built of materials and in turn is filled with more objects to be used by fewer people.

The “individuation” of products also materializes. The dominant American social model is not simply to own one’s home but to have access to products and services customized for more and more niches. Packages of “portion-controlled” prepared food and, more generally, product proliferation exemplify individuation. From 1980 to 1993 the number of new products introduced in supermarkets grew at an average compound rate of 14 percent per year. More than seventeen thousand new items appeared on store shelves in 1993.21

Although many products saturate the consumer markets temporarily, they often rematerialize at a higher level. One example is the telephone. During the 1930s, telephones saturated in the United States at a rate of two for every ten persons.22 Starting about 1940, phones found new markets—the result of prosperity, new functions and fashions, and better performance. After 1970 it became difficult to keep track of the number of phones in operation in the United States. It is not surprising that the Bell System crumbled when it contained more than one hundred million objects at the level of the end user. Numerous phones now ring for every American. A continuation of this trend will bring the United States to many hundreds of millions of devices by 2020. On average each new generation of devices is smaller and lighter than its antecedents and performs more functions, such as fax transmission, voice mail, and wireless mobile telecommunications. An interesting question is whether the total mass of the telecommunications system, including cables and other equipment and facilities, has changed much since its initial formation earlier in the century. Revenge theory suggests that the overall system growth may offset the efficiency gains in its components.

Dematerialization and Wastes

Poor data, unreliable and inconsistent categorization, and infrequent surveys impede the establishment of waste trends.23 Serious interest in comprehensive rubbish data is quite recent. Moreover, some material by-products, which might otherwise flow into further productive use, become waste due to rather arbitrary labeling laws and regulations.24 One year for which comprehensive data for the United States are available is 1985 (Figure 8). Industrial wastes dominate, but 90 percent of industrial (including manufacturing) wastes can be water, so a comparison between classes may be misleading. When we simply add all of the wastes, the total in 1985 was about 10 billion metric tons, or about 115 kg per capita per day. Because a large and unknown fraction of this amount is water, it cannot be compared with our 50 kg per capita per day estimate of material use. Further research might lead to such a comparison and rough total guesses of net long-lived materialization. Instead, here we cautiously provide some comparisons of waste categories over time.

Sewage sludge almost doubled between 1972 and 1992 in the United States to 5.4 million dry metric tons, about 21 kg per capita annually.25 The increase does not indicate a change in human metabolism but rather in population growth and increased treatment of waste. The main source of ash is coal power plants. A rule of thumb is that about 10 percent of all coal burned remains as bottom ash, boiler slag, or fly ash captured by air pollution devices. As coal consumption declines, so does ash production, though flue-gas desulfurization may increase sludge while decreasing air pollution. Inclusion of coal and wood ash in historical analyses could substantially modify the picture of waste trends; it would flatten the recent rise by increasing the amount of waste generated in earlier periods. In 1990, the amount of coal ash produced equaled about 350 kg per American. Hazardous wastes include several hard-to-define subcategories, and no long-term figures are available.26 For such wastes environmental effects may sometimes be measured in micrograms rather than megatons. According to the US Environmental Protection Agency (EPA), in 1985 total hazardous waste generation was 271 million metric tons, while in 1987 it was 238 million, or roughly 1 t per capita. A related category is toxic chemicals and compounds released to air, water, and land by industrial facilities. Allowing for considerable uncertainty, EPA reports indicate that the total amount declined from about 2.2 million metric tons (4.8 billion pounds) in 1988 to 1.4 million metric tons (3.2 billion pounds) in 1992, or about 5.6 kg per American.27

In absolute terms, municipal solid wastes (MSW) in the United States rose from 80 million metric tons in 1960 to 188 in 1993, or about 725 kg per capita.28 About one-third of MSW by weight consists of packaging products. While MSW increased by about 1.5 percent per capita annually in the United States between 1960 and 1993, the amount of American trash generated per unit of GNP decreased, or dematerialized, on average by about 0.3 percent per year despite a recent upturn (Figure 9). As shown in Figure10, reported waste generation varies markedly by country. Even among advanced industrialized nations, reported waste varies by up to a factor of three, which may partly reflect differences in categorization. The German data show a tight lid on trash, and in fact Germany seeks to reduce its packaging waste by 80 percent.29 Although it is hard to make global generalizations, the United States by all measures stands apart in its high level of trash generation.

Questions and Conclusions

Is it possible to bring together existing evidence in a general theory of materialization and dematerialization? Bernardini and Galli30 have proposed a two-part theory that merits attempts at validation. The first part of their theory is that new materials substitute for old in subsequent periods of time,31 and each new material shows improved physical properties per unit quantity, thus leading to a lower intensity of use. The second part of the theory applies to the development of nations or regions. The concept is that countries complete phases of their development sequentially at roughly the same value of per capita GDP, but the intensity of use of a given material declines depending on when each country completes its development, as the late-arriving economies take advantage of learning curves.

The Bernardini and Galli theory is hopeful for dematerialization. It implies that continued research and development of materials will bring about substantial gains and that global development will not dumbly imitate the behavior of the early developing nations. Thus, for example, China and India will never reproduce the pattern of per capita materials flows of the United States, even if their GDPs grow dramatically.

While appreciating this general logic for dematerialization, what does the actual evidence show so far for the United States? Our survey suggests the following:

1) With regard to primary materials, summary ratios of the weight of materials used to economic product appear to be decreasing due to materials substitution, efficiencies, and other economic factors. The tendency is to use more scientifically selected and often artificially structured materials.32 These may be lighter, though not necessarily smaller. The value added clearly rises with the choice of material, but so may aggregate use.

2) With regard to industry, encouraging examples of more efficient materials use exist in many sectors, functions, and products. Firms search for opportunities to economize on materials, just as they seek to economize on energy, labor, land, and other factors of production. However, the taste for complexity, which often meshes with higher performance, may intensify other environmental problems, even as the bulk issues lessen.

3) As consumers, we profess one thing (that less is more) and often do another (buy, accrete, and expand). We see no significant signs of net dematerialization at the level of the consumer or saturation of individual material wants.

4) With regard to wastes, recent, though spotty, data suggest that the onset of waste reduction and the rapidity with which some gains have been realized as well as the use of international comparisons indicate that very substantial further reductions can take place.

An overall assessment clearly requires an ensemble of measures under the rubric of dematerialization. System boundaries matter a great deal, whether they be nations, regions, economic sectors, firms, households, or products. In general, viewing the environmental impact of a product in isolation from the total system is simplistic. For example, examined in isolation, a computer could be deemed environmentally unfriendly because the production of the printed circuit boards, logic and memory chips, and display screens requires a large quantity of hazardous chemicals and solvents and heavy metals. This conclusion could also be based on its propensity for the consumption of paper and energy. However, the operation of the same computer in an industrial setting could increase efficiencies in a manufacturing process and reduce the consumption of energy and raw materials and the generation of waste. What a cursory scrutiny might identify as a local maximum could be a global minimum in terms of adverse environmental impacts. Thus, we must measure products, product life cycles, sectors, and the total materials economy at several stages, denominated in various ways.

A logical next step in research is to develop a self-consistent scenario for a significantly dematerialized economy and to explore the changes in technology and behavior needed to achieve it. Such an exercise should include careful examination of hazards as well as benefits to the environment associated with a qualitatively and quantitatively new materials economy.

Clearly, intensive research in materials science and engineering, sensitive to environmental properties, is a key to dematerialization. Humanity has passed from the ages of stone, bronze, and iron to an age in which we deliberately employ all ninety-four naturally occurring elements of the periodic table. We must learn to use the elements even better, in a way compatible with our long-term well-being.

In conclusion, we return to the observation that substantial progress has been made over the past century in decoupling economic growth and well-being from increasing primary energy use through increased efficiency. Decoupling materials and affluence will be difficult—much harder than decoupling carbon and prosperity. Objects still confer status, and they take their revenge.


We gratefully acknowledge assistance from John D. C. Little, Perrin Meyer, and Umer Yousafzai. We also thank the Austin Multiple Listing Service, Inc. and Borris Systems for providing access to their database of Austin residences.


1E. Tenner, Why Things Bite Back: Technology and the Revenge of Unintended Consequences (New York: Knopf, 1996).

2Robert Herman, Siamak A. Ardekani, and Jesse H. Ausubel, “Dematerialization,” in Jesse H. Ausubel and Hedy E. Sladovich, eds., Technology and Environment (Washington, D.C.: National Academy Press, 1989), 50-69.

3Robert A. Frosch, “Industrial Ecology: A Philosophical Introduction,” Proceedings of the National Academy of Sciences of the USA 89 (3) (1992): 800-803.

4H. E. Goeller and A. M. Weinberg, “The Age of Substitutability: What Do We Do When the Mercury Runs Out?” Science 191 (1976): 683-689.

5Our recalculation of demandite for 1968 differs from the results obtained by Goeller and Weinberg. We believe that the discrepancy is due to our using different data inputs for calculating the silicate and calcium carbonate contributions to demandite. Our result of 12.33 percent for SiO2 is slightly larger than their 11.15 percent figure, and our result of 0.15 percent for CaCO3 is considerably smaller than their figure of 4.53 percent. We note that this disparity in results does not alter the conclusions drawn from the table, as it hardly affects the dominant position of the hydrocarbons, and the environmental effects of these two minerals are essentially equivalent and benign.

6Nebojša Naki¬enovi¬, “Freeing Energy from Carbon,” Dædalus 125 (3) (Summer 1996).

7D. G. Rogich et al., “Materials Use, Economic Growth, and the Environment,” paper presented at the International Recycling Congress and REC’93 Trade Fair (Washington, D.C.: US Bureau of Mines, 1993).


9Iddo K. Wernick and Jesse H. Ausubel, “National Materials Flows and the Environment,” Annual Review of Energy and Environment 20 (1995): 463-492.

10See also M. Ross, E. D. Larson, and R. H. Williams, Energy Demand and Material Flows in the Economy, PUCEE Report No. 193 (New Jersey: Princeton University Center for Energy and Environmental Studies, 1985).

11US Bureau of Mines, Mineral Facts and Problems (Washington, D.C.: US Government Printing Office, various years).

12Modern Plastics 37 (5) (1960); and personal communication from Joel Broyhill, data on the US production of plastics resin, statistics department, Society of the Plastics Industry, Washington, D.C., 20 August 1993.

13US Bureau of Mines, The New Materials Society: Volume I-III (Washington, D.C.: US Government Printing Office, 1990).

14R. J. Garino, “Can Recycling, Back on Track,” Scrap Recycling and Processing (May/June 1993).

15US Bureau of Mines, The New Materials Society: Volume I-III.

16Iddo K. Wernick, “Dematerialization and Secondary Materials Recovery: A Long-Run Perspective,” Journal of the Minerals, Metals, and Materials Society 46 (4) (1994): 39-42.

17D. T. Allen and N. Behmanesh, “Wastes as Raw Materials,” in Braden R. Allenby and Deanna J. Richards, eds., The Greening of Industrial Ecosystems (Washington, D.C.: National Academy Press, 1994), 69-89.

18Robert A. Frosch and N. E. Gallopoulos, “Strategies for Manufacturing,” Scientific American 260 (1989): 144-152.

19See Lee Schipper, “Life-Styles and the Environment: The Case of Energy,” Dædalus 125 (3) (Summer 1996).

20Personal communication from George Bennett, statistics department, Household Goods Carriers Bureau, Alexandria, Va., 14 October 1993.

21Personal communication from Lynn Dornblaser, statistics department, New Product News, Chicago, Ill., 8 June 1994.

22US Bureau of the Census, Historical Statistics of the United States, Colonial Times to 1970 (Washington D.C.: US Government Printing Office, 1975).

23William Rathje and Cullen Murphy, Rubbish (New York: Harper Collins, 1992); and US Congress, Office of Technology Assessment, Managing Industrial Solid Wastes from Manufacturing, Mining, Oil and Gas Production, and Utility Coal Combustion, OTA Report No. OTA-BP-O-82 (Washington, D.C.: US Government Printing Office, 1992).

24As discussed by Robert A. Frosch, “Toward the End of Waste: Reflections on a New Ecology of Industry,” Dædalus 125 (3) (Summer 1996).

25D. Jin, Optimal Strategies for Waste Management: The Ocean Option (Woods Hole, Mass.: Marine Policy Center, Woods Hole Oceanographic Institution, 1993).

26D. T. Allen and R. K. Jain, eds., Hazardous Waste & Hazardous Materials 9 (1) (1992): 1-111 (a special issue on national hazardous-waste databases).

27INFORM, Toxics Watch (New York: INFORM, 1995).

28US Environmental Protection Agency, Characterization of Municipal Solid Waste in the United States: 1992 Update, Final Report, EPA Report No. 530-R-92-019 (Washington, D.C.: US Environmental Protection Agency, 1992); and US Bureau of the Census, Statistical Abstract of the United States: 1995, 115th ed. (Washington, D.C.: US Government Printing Office, 1995).

29Bette K. Fishbein, Germany, Garbage, and the Green Dot (New York: INFORM, 1994).

30O. Bernardini and R. Galli, “Dematerialization: Long-Term Trends in the Intensity of Use of Materials and Energy,” Futures (May 1993): 431-448.

31J. C. Fisher and R. H. Pry, “A Simple Model of Technological Change,” Technological Forecasting and Social Change 3 (1971): 75-88.

32L. J. Sousa, Towards a New Materials Paradigm (Washington, D.C.: US Bureau of Mines, 1992).

Iddo K. Wernick is Research Associate with the Program for the Human Environment at The Rockefeller University.

Robert Herman is L. P. Gilvin Centennial Professor Emeritus in Civil Engineering and Professor of Physics at the University of Texas at Austin.

Shekhar Govind is Assistant Professor of Civil and Environmental Engineering at the University of Texas at Arlington.

Jesse H. Ausubel is Director of the Program for the Human Environment at The Rockefeller University.

National material metrics for industrial ecology

Industrial ecology studies the totality of material relations among different industries, their products, and the environment. Applications of industrial ecology should prevent pollution, reduce waste, and encourage reuse and recycling of materials. By displaying trends, scales, and relations of materials consumed, emitted, dissipated, and discarded, metrics can expose opportunities to improve the performance of industrial ecosystems.

Metrics can indicate environmental performance at all levels: factory, firm, sector, nation, and globe. National metrics focus attention on collective behavior, particularly in a large country such as the United States whose economy sums the actions of more than 250 million people and 3 million for profit corporations. The federal government assembles national data on a vast array of activities. The need is for a coherent set of metrics that enables efficient diagnosis of national environmental conditions and provides help in considering strategies for the future.

The need to develop environmental metrics is particularly strong for materials. National materials consumption indicates the structure of national industrial activity and its extent. Environmentally important industries such as mining, forestry, agriculture, construction, and energy production can be evaluated based on their material requirements and outputs. Despite their ubiquity and close association with environmental quality, materials have received little systematic analysis, particularly as compared with energy. This inattention stems in part from the heterogeneity of materials used in the modern economy and the myriad enterprises involved in transforming, processing, and disposing of materials and goods.

With the help of the Bureau of Mines, we have developed an environmentally oriented framework for characterizing material flows in the United States. Choosing metrics requires a grasp of the diversity and enormity of U.S. materials flows (Figure 1). Our framework considers primarily three components: inputs to the economy (including imports), outputs (including exports), and extractive wastes. We aim for comprehensiveness in this framework in the sense that we do not want to “lose” materials and would eventually hope to record the complete materials balance. Our choice of inputs and outputs as major categories derives from the simplest of materials-flow models. We group extractive wastes separately because they represent immense mobilizations of materials readily distinguished from commodities, products, and other wastes. We use previously published data for all the values indicated and generally adhere to existing classifications.

We segment inputs into energy, construction minerals, industrial minerals, metals, forestry products, and agricultural products. We class outputs as domestic stock, atmospheric emissions, other wastes, dissipation, and recycled materials. Imports and exports represent the masses of major individual commodities and classes of commodities crossing U.S. borders. Extractive wastes include residues from the mining and oil and gas industries. We account for water in Figure I but not in the material metrics because the weight and omnipresence of this resource would obscure what remains. We also omit consumption of atmospheric oxygen for biological respiration and in industrial processes. 3 We do not explicitly consider manufactured chemical products, but do include the mass of feed stocks used for organic and inorganic chemical production.

Materials have the advantage of offering a single unit of measure, weight, that allows for direct comparison across a broad range of material types. Kilograms and tons can hide variables such as volume, land disturbance, toxicity, 4 and other environmentally important qualities associated with materials that weight measures do not reflect. Nevertheless, weight does provide a reasonable starting point for appreciating the structure and scale of major activities affecting national environmental quality.

National material metrics do not obviate the need for monitoring environmental variables locally. Rather, they complement smaller scale metrics that underscore the spatial distribution of problems and needs. In this respect, they resemble national economic indicators, such as gross domestic product (GDP). In addition, national materials metrics offer the prospect of capturing environmentally significant trends and relations not captured in the current regulatory framework, which tends to emphasize reporting by media, especially air and water, rather than along the functioning of the economic system.


We propose eight general classes of metrics to indicate the current status and salient trends in national materials use as they influence environmental performance (Table 1). Most address either the productivity or the efficiency of resource use. Others indicate trends in the size and composition of materials use. Some metrics offer a means for quantifying aggregate environmental changes resulting from current national activities. Although some of the metrics are novel, others are already employed but gain meaning from the more systematic context. Although imperfect, this initial classification is intended to stimulate subsequent inquiry into the development of material metrics and the logic sustaining them.

Absolute National and Per Capita Inputs

The total mass of materials consumed by a nation, or individual members of its population, offers an indicator that tangibly values resource use. The components of the total differ in kind (and often in the accuracy of the supporting data), but their sum provides a benchmark for environmental management.In 1990, each American mobilized on average about 20 metric tons of materials, or over 50 kg/day. The breakdown in Figure 2 equates with Figure I on national flows at the level of the individual American. This sum may be similar in other industrial nations. For example, estimates of Japanese materials use in 1990 total 52 kg per capita per day, a number closely comparable to the U.S. estimate (Gotoh, 1997).

The dynamics of per capita resource use as well as the efficacy of various policy initiatives aimed at affecting it could be gauged by comparing this number over time and across nations. More detailed metrics would took at consumption of classes of materials, such as energy fuels or agricultural minerals, and environmentally significant individual materials, such as lead.

Composition of Material Inputs to the National Economy

With economic development and technical change, the demand for materials evolves. Input composition reveals economic structure and dynamics and helps anticipate environmental consequences.

For example, environmental import attaches to the evolving ratio of the three fossil fuels used for energy, coal, oil, and gas, or in more elemental terms to the balance of hydrogen and carbon used to power and heat the nation (Marchetti, 1989; Nakicenovic, 1996). Although not used for energy, nonrenewable organic materials derived from petroleum and natural gas such as petrochemicals, plastics, asphalt, fibers, and lubricants comprise an appreciable fraction, about 6 percent, of total hydrocarbon consumption (Bureau of Mines, 1991a). The endpoints for these materials matter environmentally and as such merit their own distinct measure as a fraction of all hydrocarbon consumption.

The choice of structural materials indicates trends relevant to national environmental performance as well. Demand for properties in industrial and consumer goods influences selection among the major classes of structural materials: metals, ceramics and glasses, and polymeric materials including wood (Ashby, 1979). These materials range widely in their ability to bear loads, resist fracture, and operate in harsh thermal conditions. They also differ in typical densities (Figure 3). Similarly, they possess varying environmental attributes such as the energy needed, waste generated, and toxins released to the environment during extraction and processing. Comparing the energy needs for processing an equal mass of aluminum, steel, cement, and polystyrene yields an approximate ratio of 85:10:2:1 (Agarwal, 1990; Hocking, 1991). Of course, materials rarely substitute for one another in products in a 1:1 mass ratio.

Historically, substantial scientific and engineering effort has been directed at improving the properties of metal alloys. Future gains may come in the area of polymers stiffened in the direction of loading, ceramics toughened to resist fracture, and composite materials designed to accentuate the best qualities (i.e., light, strong, and tough) of each material class. Although advanced materials may be difficult to reprocess, recyclability is not the single measure of environmental friendliness. This property must be weighed against gains derived from shifting to materials that perform functions using less mass, require less energy to process, and generate less incidental waste.

The composition of the food we consume, directly or indirectly, impacts the environment. Reduced national meat consumption accompanied by a rise in fruit, grain, and vegetable consumption diminishes the acreage used for grazing and feed in favor of less land-extensive crops. Cultivation of legumes and rice affects nitrogen fixation rates and atmospheric methane concentrations, respectively. Fertilizer and pesticide use rates are tailored to specific crops. In this case as with the others, input composition metrics clarify the environmental dimension of varying the mix of materials society consumes and shed light on paths for future development.

Intensities of Use

Intensity-of-use metrics show the evolution of individual materials used in the national economy by indexing primary, as well as finished, materials to GDP (Figure 4; also, see Malenbaum, 1978). These measures inform policy choices relating to natural resources by helping to gauge developmental status and to define realistic goals that integrate economic growth and improved environmental quality. In the energy sector, the declining intensity of carbon use, “decarbonization,” of the U.S. economy relative to economic activity as well as energy use has been well established (Figure 5).

Intensity-of-use metrics also can show physical resource efficiency. For example, in 1990, the ratio of agricultural produce (e.g., grain, hay, fruit, and vegetables) to fertilizer inputs (e.g., nitrogen compounds and phosphates) was roughly 10:1 (Bureau of Mines, 1991b; United States Department of Agriculture, 1992). The ratio of food actually consumed by humans to mineral inputs is considerably lower. Other sectors using raw inputs as well as auxiliary materials for production (e.g., iron ore, coke, and lime for steel; wood and chemicals for paper) could apply similar environmental performance measures.

“Virginity” and Recycling Indices

A virginity, or raw materials, index measures the ratio of national raw materials use to total national inputs. It monitors the distance a society must go to stop extracting materials from the earth and sustain itself through its above-ground materials endowment and recycling. For 1990, recycled material accounted for about 5 percent of all inputs to the U.S. economy by weight (Rogich, 1993). Impeding the increase of this fraction are the heterogeneity of materials in the waste stream, industrial demand for materials with highly specific properties, and cumbersome regulations. These factors combine to shrink the pool of resources that can be used as inputs to production (Frosch, 1994; Wernick, 1994).

Among specific materials of interest are metals and wood. The fraction of secondary to total metals consumption indicates both the efficiency of metals reuse from new scrap generated within industry and the success in recycling old scrap recovered from obsolete products such as automobiles. Recycling today accounts for over half the metals consumed in the United States (Figure 6; Rogich, 1993). However, recovery remains below 10 percent for arsenic, barium, chromium, and other biologically harmful metals listed in the Toxic Release Inventory (Allen and Behmanesh, 1994). The difference between annual forest growth and removal of growing stocks offers a simple measure of incremental changes in forest volume. For the period 1970-1991, U.S. forests gained an average of over 150 million cubic meters of timber annually, augmenting existing timber volume at an annual rate of about 0.7 percent (United States Department of Agriculture, 1992).

Waste (Emission) Intensities

Waste intensities measure residuals and emissions per unit of output in physical or economic terms. Corporate practice increasingly evaluates the ratio of wastes to total firm output, including products and salable by-products (3M Corporation, 1991) and seeks uses for wastes (Ahmed, 1993; Edwards, 1993) as efficiency measures. National indicators would assess “green” productivity by evaluating the amount of materials considered as waste against various output categories. Figure 7 shows long-term trends of U.S. municipal solid-waste (MSW) generation, sulfur dioxide emissions, and emissions of nitrogen oxides indexed to economic activity. Industrial wastes are strong candidates for analysis using this metric. However, dry weight data on industrial wastes rarely exist or are hard to obtain (United States Congress, Office of Technology Assessment, 1992).

Leak Indices

Leak indices measure the ratio of outputs emitted and dissipated to total outputs, thereby quantifying the proportion of materials lost to further productive use and dispersed into the environment. Applying this measure allows for easier identification and isolation of “holes” in the system and focuses efforts to plug them.

Geographical information on nutrient and heavy-metals loadings aids improvement of accounts of dissipated materials. National efforts in this area are well established but incomplete. The National Oceanic and Atmospheric Administration (1993) estimates coastal discharges of nutrients (nitrogen, phosphorus), heavy metals (e.g., arsenic, lead, cadmium), and petroleum hydrocarbons in U.S. estuaries in the National Coastal Pollution Discharges Inventory. Estimates of inland nutrient discharges and metals deposition rates are sparse at best. Extending these measures to the entire nation would be laborious but worthwhile from the perspective of national environmental management.

Environmental Trade Index

An environmental trade index indicates the degree to which the nation is retaining or displacing pollution through international trade. Exporting raw materials consumes national resources and scars the domestic landscape. Using domestic industry to convert imported materials into finished goods and prepare indigenous materials for export can damage the environment in other ways. Despite intense interest in the monetary balance of U.S. foreign trade, the environmental profile of trade flows has received scant attention until recently, in the context of trade with Mexico.

By weight, commodities dominate trade. The mass of manufactured products traded contributes little to the total but may be responsible for domestic waste generation and discharges to the environment. During 1990, exports were dominated by agricultural products (33 percent), coal (23 percent), and chemicals (10 percent), all goods associated with domestic pollution. In the same year, crude oil and petroleum products accounted for over 60 percent of U.S. imports by weight, with metals and minerals accounting for another 20 percent (Bureau of the Census, 1993). We lack ready means to assess how the spatial redistribution of economic functions would affect environmental quality.

Extractive Waste Ratios

Extractive waste ratios measure resource efficiency in the mining industry. Recalling Figure 1 confirms the massiveness of wastes generated in this sector. Rock removed to expose mineral and ore bodies accounts for most of this waste. This material may be harmless, but exposing raw earth to wind and water can raise local acidity levels and allows for transport of trace elements. The sheer amounts of materials mobilized in mining and the economic incentive to minimize wastes combine with environmental objectives to advocate metrics of efficiency. Geological characteristics primarily determine overburden and tailings generated, but judgmental variables also affect mine wastes. One measure, subject to some physical constraints, is the amount of mine wastes per ton of mineral or ore mined, or primary metal produced. A separate useful measure, already used at the company level, looks at other inputs such as water and energy use per ton of finished product (Chiaro and Joklik, 1997). Measures of the recovery of by-products (e.g., methane in coal seams, sulfuric acid from smelter emissions, and metals from flue dusts) provide further examples of environmental indicators for the mining and mineral processing sector.


Industry operates and people behave within a system that evolves to satisfy human wants and uses a dynamic set of means to achieve them. As a discipline, industrial ecology discourages reducing the system to components and examining them in strict isolation. The challenge for national material metrics, as well as other national environmental metrics, is to quantify and integrate relevant data that elucidate the primary structure and development of the system from an environmental perspective.

National material metrics rely on empirical data. Various agencies of the federal government collect relevant data for one purpose or another. However, unless coordinated, the data do not fully support existing metrics and limit the scope for future ones. Procedural changes aimed at synchronizing data collection among various federal departments and agencies to build a single base (year) would amplify the benefits of existing collection efforts. Equally important from an environmental perspective is the development of standardized definitions for classifying material commodities to erase confusion leading to omissions and double counting of material components.

Accurate data on wastes are the hardest to obtain. Companies collect little or no data for many waste streams due to the actual or perceived absence of economic value. High disposal costs and regulatory requirements have improved waste accounting practices at many firms, but wastes have yet to receive the respect that marketability confers. Among the main goals of industrial ecology is exploring potential markets for waste materials. Currently, the dearth of reliable information available for wastes is one of the factors blocking progress. Better information would improve the market climate for wastes and at the same time help to develop metrics that assess their relative impact nationally.

Although improved national environmental metrics go hand in hand with better databases, metrics are not meant simply to compile information. Their purpose is to embed the data in a context that recognizes the larger system and is relevant to how it works. Good environmental indicators exist, but too often remain detached from each other and from an unambiguous framework. Appropriate metrics should correlate individual indicators and clarify the relation of each one to the whole. To illustrate, citing fertilizer usage rates without reference to agricultural productivity is misleading and causes unwarranted alarm. Conversely, extolling the environmental virtue of a lighter consumer product without examining the life-cycle implications of its fabrication and disposal is premature. To enhance their value and minimize misuse, commentary and interpretation should accompany the publication of metrics.

To adequately respond to complex questions of environmental performance requires both context and an array of metrics. For example, is the nation beginning to “dematerialize,” that is, effectively decouple overall materials consumption from continued economic growth? For the U.S. energy sector the answer has been in the affirmative. Efficiency gains and the shift away from heavy manufacturing have modified the traditional relation between energy consumption and economic growth in the United States. Single indicators (i.e., kilowatt hours consumed/$GDP) elegantly illustrate this development. To have similar confidence regarding materials will require a more elaborate set of measures that are sensitive to the diverse structure of contemporary materials use and the many forces affecting its dynamics (Wernick et al., 1996). National materials metrics would refine how such questions are articulated and provide the basis for more convincing answers than are now available.

Looking to the future, national materials metrics help order the national research agenda for materials science and engineering (National Academy of Sciences, 1989). At over 50 kg per day per American, even the rough profile developed here demonstrates the need for meshing environmental and materials research. Metrics highlight the locations and relative urgency of incorporating environmental goals into materials research programs. Significantly, these goals often overlap with factors affecting the bottom line such as reducing inputs, improving efficiency, recycling, and complying with environmental regulations.

Future materials fluxes, including both products and by-products, may even exceed contemporary ones in size. To make them environmentally compatible, we need better methods for analyzing their current condition and anticipating future changes. To achieve the goal of a more circular economy, society needs to consider its materials legacy as a dowry to future generations, rich in valuable ore. By capitalizing on the “mines above ground” or scrap piles for materials, wastes from extraction and disposal grow dispensable. We can imagine an industrial ecosystem in which emissions, including carbon and water vapor, are captured and complex waste streams are separated to recover the value and utility of their components. The discipline of creating national materials metrics is a useful start to creating a consistent, realistic long-range technical vision.


We are indebted to Donald Rogich, Jim Lemons, and Grecia Matos at the Bureau of Mines for data and ideas on materials taxonomy.


FIGURE 1 U.S. materials flows, circa 1990. All values are in million metric tons per year. Consumptive water use is defined as water that has been evaporated, transpired, or incorporated into products and plant or animal tissue and is therefore unavailable for immediate reuse. For a detailed description of this figure and data sources see Wernick and Ausubel (1995).

FIGURE 2 Per capita material flows, United States, circa 1990. All values are in kilograms per day. See caption for Figure 1 for further explanation.

FIGURE 3 Range of physical properties for structural materials. Young’s modulus is a measure of material elasticity. Toughness is a measure of resistance to fracture. Toughness is measured in units of joules per square meter of fracture surface (G) and is here normalized to Young’s modulus (E) times atomic size (a). SOURCE: After Ashby (1979). Other sources include Carter and Paul (1991) and Hodgman (1962).

FIGURE 4 Materials intensity of use in the United States, 1900-1990. This metric conveys the evolving materials requirements of an economy over time. Consumption data are indexed to annual GDP in constant 1982 dollars. (For example, in 1900, U.S. phosphate consumption was 1,515,425 metric tons and gross national product was $261.5 billion, equivalent to about 5.8 metric tons per million dollars GDP. In 1990, 4,692,919 metric tons of phosphate were consumed and GDP was $4,120 billion, equivalent to about 11.2 metric tons per million dollars GDP.) All intensity-of-use values are normalized to unity at 1940 with the exception of plastics, which is indexed to 1942. SOURCES: Modern Plastics Magazine (1960); Bureau of the Census (1975, 1992). Data on U.S. production of plastics resin are from Broyhill, Statistics Department, Society of the Plastics Industry, Washington, D.C., personal communication, August 20, 1993.

FIGURE 5 Diminishing carbon intensity of per capita GDP in the United States, 1800-1988. Carbon intensity is carbon consumed for energy divided by annual GDP in constant 1985 dollars. SOURCE: After Gruebler and Fujii (1991).

FIGURE 6 Ratio of secondary to primary metal consumption, United States, 1962-1991. SOURCE: Rogich (1993).

FIGURE 7 Waste intensities in the United States, 1940-1990. Municipal solid-waste (MSW) discards, and sulfur dioxide and nitrogen oxide emissions, indexed to GDP in constant 1987 dollars. SOURCES: Bureau of the Census (1975, 1994).


  1. In this paper we draw on other work by the authors (Wernick and Ausubel, 1995) that contains detailed data supporting the metrics presented here.
  2. Domestic stock refers to materials embedded in structures and products not discarded for a period longer than 1 year.
  3. We include atmospheric nitrogen fixed into NOx emissions as well as for ammonia production. We omit estimates of the mass of soil eroded during agricultural operations.
  4. A clear example of this is annual total U.S. dioxin and furan emissions, which are counted in kilograms rather than tons, yet have considerable environmental impact (Thomas and Spiro, 1995).
  5. A complete net carbon balance for forests includes annual carbon flows in trees, soil, forest floor, and understory vegetation. Since 1952, the amount of carbon stored in U.S. forests has grown 38 percent, adding about 9 billion metric tons of carbon (Birdsey et al., 1993).


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Ahmed, I. 1993. Use of Waste Materials in Highway Construction. Park Ridge, N.J.: Noyes Data Corp.

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Birdsey, R. A., A. J. Plantinga, and L. S. Heath. 1993. Past and prospective carbon storage in United States forests. Forest Ecology and Management 58:33-40.

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Bureau of Mines. 1991b. Mineral Commodity Summaries. Washington, D.C.: Bureau of Mines.

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Bureau of the Census. 1992. Statistical Abstract of the United States: 1992, 112th ed. Washington, D.C.: U.S. Government Printing Office.

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Chiaro, P., and F. Joklik. 1997. Environmental strategies in the mining industry: One company’s experience. Pp. 165-181 in The Industrial Green Game: Implications for Environmental Design and Management, D. J. Richards, ed. Washington, D.C.: National Academy Press.

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Nitrogen on the land: overcoming the worries – lifting fertilizer efficiency and preserving land for nonfarming uses

Nitrogen Fertilizer

In 1931, Karl Bosch received the Nobel Prize for making nitrogen fixation practical.  Like many new technologies, synthetic nitrogen fertilizer enjoyed strong growth, from 1.3 Tg nitrogen in 1930, to 83 Tg in 1998.  (One Tg equals a trillion grams or a million metric tons.  These data refer to the fertilizer year 1 July-30 June.  Thus, for example, 1998 data are for 1998-99.)  By “synthetic nitrogen fertilizer,” we mean commercial product, with almost all the nitrogen fixed by the Haber-Bosch process — in contrast to manure, guano, oil meals, and packing-house waste.

Is the use of nitrogen fertilizer growing exponentially?  No.  A constant percentage increase accelerates a curve exponentially.  This is not what is happening with nitrogen fertilizer.

After an explosive annual growth of 14% during the period 1945-56, global growth of nitrogen fertilizer use slowed to 8% as 1970 approached.  Growth then slowed further to 5% yearly during 1976-85, and to less than 1% during 1986-98.  In Europe and the United States, which adopted the new technology early, growth slowed even sooner.  Since 1976, use in Europe and the U.S. has grown 1% or less yearly, and sometimes has actually fallen.

Like numerous products that saturate their market, nitrogen fertilizer fits not an ever-rising exponential growth pattern, but an S-shaped logistic one (Frink et al. 1999).

Nitrogen Deposition

The nitrogen falling from the atmosphere, mostly as NO3-nitrogen and NH4-N (ammonium-N), can be measured by simply collecting it in the open as “bulk deposition.”

“Wet deposition” is collected only during precipitation.  “Throughfall” is nitrogen deposited on forest canopies and eventually falling or washing down in precipitation.  Nineteenth century agronomists, who were  concerned about deposition on crops, collected bulk deposition.  More recently, scientists concerned about acid rain (caused by sulfur and nitrogen) collected wet deposition, and ecologists concerned about accumulation of nitrogen in forests collected throughfall beneath trees.

In order to understand nitrogen deposition, we must compare it with some scale.  Synthetic fertilizer use has increased approximately 100 fold.  Concurrently, worldwide NO3-nitrogen from high temperature combustion in car motors and power plants has risen 10-fold to about 20 Tg.

Farmers increase crop yields with 100 to 200 kg nitrogen ha-1 (kilograms per hectare).    For prevention of eutrophication and 95% safety, Europe has established incremental critical loads of 3-10 kg ha-1  (with standards of less than 3 and more than 10 in some places) (Posch et al. 1997).

In infertile soil made responsive by fertilization with other nutrients, increments as little as 10 kg, but sometimes not less than 54 kg, nitrogen ha-1 decreased biodiversity (Tilman 1987).  Early in the 20th century, bulk deposition in Europe and the U.S. was 4 to 7 kg ha -1.

Anyone smelling a barnyard knows local deposition of NH4-N can be high.  In the Netherlands, a local throughfall of 100 kg ha-1 attributed to animals will affect vegetation (Ivens, 1990).  The manure km-2 in the Netherlands is five times that in the quintessential U.S. agricultural state of Iowa.   Locally, where animals are concentrated, throughfall can approach farmers’ fertilizer rates.

However, deciding whether widespread, rather than local, increase of nitrogen deposition accompanied the use of more nitrogen fertilizer requires measurements spanning decades at several places.  For a comparison that offers data over a period as long as the growth of fertilizer use, we must turn to the simple, robust measure of bulk deposition.  In Rothamsted, England, annual deposition rose a total of about 1 kg ha-1 between 1888 and 1966.  Bulk deposition of 8.7 kg (estimated from wet deposition during 1987-96 at nearby Woburn) confirms an increase, perhaps 5 kg ha-1 during the century.

In northern Netherlands, bulk deposition increased about 7 kg from 6.7 kg ha-1 at Groningen during 1908-10 to 14.5 kg at nearby Kollumerwaard during 1994.  In Sweden, it changed little from the 5.1 kg ha-1 at Flahult in 1909 to 7.1 kg in 1996-97 at three nearby stations (Frink et al. 1999).

At Geneva and at Ithaca, New York, during the first quarter of the 20th century, annual bulk deposition ranged from 4 to 8 kg ha-1.  About 6 kg was also deposited at Mays Point and Huntington Forest, New York, during 1965-80 and also at Hubbard Brook, New Hampshire, during 1972-92 (Frink et al. 1999).  In the northeastern United States during the 20th century, bulk deposition changed little.

One should not be surprised that nitrogen fertilizer use and widespread increase of nitrogen deposition did not rise in tandem.  Except for escape of some ammonia fertilizer and dust and a little NO2, no direct path puts fertilizer nitrogen in the air for deposit.  Also, even 80 Tg fertilizer nitrogen plus 20 Tg NO3-nitrogen from high temperature combustion is insufficient to increase widespread deposition significantly; in the impossible case of all 100 Tg being deposited, it would average only about 2 kg ha-1 on Earth.  The low concentration of nitrogen in Greenland precipitation (Mayewski et al. 1990) corresponds to deposition far less than that.

Given the moderate likely rise in nitrogen use that we now project, prospects seem good for any future increase in deposition to continue making the minor contribution to plant growth that Nadelhoffer et al. (1999) have calculated is now being made.  This should pose little hazard to biodiversity.

Prospects to 2070

After overcoming worries about exponential increase and widespread rising deposition, we still come to the lurking fear of burgeoning, richer humans eventually demanding farmers smother Nature with multiples of today’s nitrogen in order to grow more food.  Although nitrogen from fertilizer can scarcely increase widespread atmospheric deposition, its leaching and pollution of water justify conservation.

Foreseeing what humanity will eventually demand requires integrating forces that drive fertilization (Frink et al. 1999).  The change of fertilizer use (see Exhibit 1) is the sum of changes in four forces:  population, GDP/capita, crop production/GDP, and the Ratio of nitrogen in fertilizer to nitrogen in crops, which we capitalize to “Ratio.”  (We neglect the small change over time in the nitrogen composition of the crop mix.)  To foresee prospects to 2070, and a population of roughly 10 billion people, we assume a population growing at 0.8% and GDP per capita at 1.8%, to lift their sum, the total GDP, to 2.6% per year.

Although wealthy people eat better than the poor do, they do not eat more in fixed proportion to GDP.  Hence, the declining ratio of crops to overall GDP has mirrored the rise of world GDP.  Whereas the GDP/Cap data in Exhibit 1 are above the zero change line, the Crop/GDP are below the zero change line, signifying a falling ratio of crops to GDP.  Expecting that the world economy will continue to favor computer chips over potato chips, we project a long decline of 1.0%/year in crop/GDP.  The sum of GDP per capita rising 1.8%, and crop/GDP falling 1.0%, still raises the crop for all persons by 2070 to the level that rich countries enjoy now.

Farmers control the fertilizer per crop as they economize inputs.  Globally, the Ratio of fertilizer nitrogen to crop nitrogen recently plummeted 2.0%/year.  In the United States, it fell earlier, and since the 1970s has fallen some 1.0%/year.  For the long pull, a decline of 0.5%/year seems reasonable as farmers continue lifting yields faster than their nitrogen fertilizer use grows.  The sum of the changing forces (0.8 + 1.8 – 1.0 – 0.5%/year) would raise world nitrogen fertilizer use 1.1%/year to 2.4 times the 1990 use by 2070.

Concern for sparing only fertilizer would be myopic.  We integrate with the saving of fertilizer the sparing of land, which is preeminent for sparing Nature.  Accordingly, we project cropland taken as well as fertilizer used (see Exhibit 2).

As a baseline for prospects to 2070, consider the situation in 1990, when 79 Tg fertilizer and 11% of world land yielded the caloric equivalent of 1,900 kg ha-1.  The 150% Ratio of fertilizer nitrogen to crop nitrogen shows that nitrogen from fertilizer, plus that from legumes and manure, far exceeds nitrogen incorporated into crops, indicating an opportunity for conservation.

Our first projection for 2070 (and assuming a population of ten billion people) is a situation in which farming has stagnated at 1990 levels in terms of yields and Ratio.  The consequent 284 Tg fertilizer nitrogen, or 3.6 times 1990 use, exceeds the 2.4 times projected above because the Ratio remains 150%.  Under this projection, cropland has expanded because population and crop per capita has grown, while yield has stagnated.  A scenario assuming use of 284 Tg nitrogen, and 38% of the land, offers the scary specter of population and wealth eventually demanding that farmers push Nature aside and smother the land in fertilizer.

Researchers can forestall that specter becoming reality with at least two levers:  Substitute nitrogen already on farms for nitrogen fertilizer, and raise yields, thus lowering the Ratio of fertilizer nitrogen to crop nitrogen.

Farms fix nitrogen in legumes and collect nitrogen in manure.  Although so-called alternative agriculture features nitrogen fixed by legumes, legumes take land and devour natural habitat.  Manure is another matter.  The estimated 80 Tg nitrogen in the world’s manure matches the 83 Tg fertilizer nitrogen used now and is significant compared to the projected 284 Tg.  Remembering that some manure nitrogen is already captured in crops, but that animals may multiply by 2070, one can envision 50 Tg of manure nitrogen substituting for fertilizer nitrogen, decreasing the fertilizer-nitrogen-to-crop-nitrogen Ratio to 124% with crops still using 38% of the land.

The ancient challenge of saving and storing nitrogen without odor continues.  Concentration of animals has focused attention on odor and increased the distances for hauling manure to fields.  It has also changed the goal from conserving nitrogen to denitrifying it and controlling odor.  A challenge for pollution prevention is replacing the negative tasks of regulating odor and returning N2 to the air with the positive task of discovering profitable and practical ways to move more of the dilute nitrogen in manure into crops.

Conserving fertilizer can also lower the Ratio of fertilizer nitrogen to crop nitrogen.  Conservation includes testing soil nitrogen and adjusting application to each site by precision farming and splitting applications during the season to avoid leaching.  Because yields divide the Ratio, higher yields can lower the Ratio and spare land, too.  Increasing yields to lower the Ratio involves breeding better crop varieties, plus removing limitations such as other nutrients, water, and pests so that crops can exploit the nitrogen provided.

While words about lowering the Ratio of fertilizer nitrogen to crop nitrogen could be mere anecdotes, statistics show farmers are in fact doing it (see Exhibit 1).  During the 1980s and 1990s the worldwide Ratio fell.  In the United States since the 1970s, the Ratio of fertilizer nitrogen to crop nitrogen fell about 1%/year.  With regard to a specific locale and crop, the Ratio for Indiana, Iowa, and Nebraska corn fell 1% to 3% per year during 1980-96 (Frink et al. 1999).  Farmers lifting the world average yield of corn, rice, soybeans, and wheat by an annual average of 1.6 to 2.3% during 1961-2000 demonstrate that higher yields also are not mere anecdotes.

A projection involving slower lifting of yields, but conserved nitrogen, shows that raising yields 1% and lowering the Ratio 0.5%/year would take 19% of land, while lowering nitrogen fertilizer use to 192 Tg.  This is the 2.4-fold increase we deem probable.

With sustained lifting of yields and conserved nitrogen, raising yields 2% and still lowering the Ratio of fertilizer nitrogen to crop nitrogen would require the same 192 Tg of nitrogen, but would actually shrink cropland 144 million hectares, which is about half the area of India, or ten Iowas.

Today, fertilizer manufacturers have idle capacity.  This, combined with weak agricultural markets in Europe and the U.S., reveal how groundless are fears that fertilizer use will soon explode.  There is little prospect of a widespread downpour of nitrogen from the air, or Nature pushed aside to relieve hunger.

Outline for Future Action

For the long run, however, and to relieve “hot spots” of nitrogen deposition, several things need to be done.  On the grand scale, regulators need to monitor two simple environmental metrics:  land spared from cropland expansion and the Ratio of fertilizer nitrogen to crop nitrogen.

On the local scale, where action is taken, fertilizer manufacturers should offer information on how to make fertilizer go further while farmers, the most hard-pressed actors, struggle to survive.  Researchers, the actors with the most opportunity to effect change, should devise affordable ways for farmers to utilize manure (now seen as a nuisance) for higher yielding crops.

Meeting these challenges will temper the use of nitrogen fertilizer, while sparing more land for Nature.


Exhibit 1.  Annual Global Changes in Population, GDP per Capita, Crop Production per GDP, and the Ratio of Synthetic Fertilizer Nitrogen to Crop Nitrogen.

Exhibit 2.  Prospects to 2070.


Frink, C.R., Waggoner, P.E., & Ausubel. J.H. (1999).  Nitrogen Fertilizer:  Retrospect and Prospect.  Proceedings, National Academy of Sciences, 96:1175-1180.

Ivens, W.P.M.F. (1990).  Atmospheric Deposition onto Forests.  Analysis of the Deposition Variability by Means of Throughfall Measurements.  Nederlandse Geographische Studies 118, 151 p.

Mayewski, P.A., et al. (1990).  An Ice-Core Record of Atmospheric Response to Anthropogenic Sulphate and Nitrate. Nature 346:554-556

Moffat, A.S. (1998).  Global Nitrogen Overload Problem Grows Critical. Science 279:988.

Nadelhoffer, K.J., et al. (1999).  Nitrogen Deposition Makes a Minor Contribution to Carbon Sequestration in Temperate Forests.  Nature 398:145-148.

Posch, M., Hettelingh, J.-P., de Smet, P.A.M., & Downing, R.J. (1997).  Calculation and Mapping of Critical Thresholds in Europe. RIVM Report 259101007.

Tilman, D. (1987).  Secondary Succession and the Pattern of Plant Dominance along Experimental Nitrogen Gradients.  Ecological Monographs 57:189-214.

Vitousek, P.M., et al. (1997).  Human Alteration of the Global Nitrogen Cycle:  Sources and Consequences. Ecological Applications 7:737-750.

Charles R. Frink ( is a soil expert and scientist emeritus at the Connecticut Agricultural Experiment Station in New Haven.  Paul E. Waggoner ( is an agronomist and meteorologist, and past director of the Connecticut Agricultural Experiment Station.  Jesse H. Ausubel ( is an industrial ecologist and director of the Program for the Human Environment at The Rockefeller University in New York City (

On sparing farmland and spreading forest


Think first not of forest but of farmland. Agriculture is shrinking. In this essay I share some views of the evolution of agriculture and then turn to their implications for forests.

Analysis of farming shows a coherent pattern of evolution from Neolithic times up to our new millennium (Marchetti 1979). All technical advances have been exploited for intensification, to increase the specific productivity of land. Yields per hectare measure the productivity of land and the efficiency of land use. Low yields squander land, and high yields spare land.

In the human beginning, as hunter-gatherers, we did not differ from many other animals. We met the pressure to grow by extending our geographical habitat as well as our range of digestible foods. In the latter regard, we made great breakthroughs with energy. Plants defend themselves against predators with a panoply of weapons. The most important are chemical and tend to make the plant indigestible and occasionally poisonous. Animals developed other defenses. Human genius was to apply thermal treatment to upset or destroy the delicate organic chemistry of defense. Boiling softens flinty rice and maize, and ovens convert past wheat into bread. Seven minutes of boiling soybeans denatures the trypsin inhibitor that would otherwise render tofu useless to us. Fire revolutionized food, permitting digestion of much plant material and seeds in particular, and in most cases improving taste as well.

Farming amplifies the production of biological material assimilable directly or by thermal treatment. Humans ally with certain plants by collaborating in their reproductive cycle and by fighting their natural enemies. We put ourselves first among selective forces, picking the plants most profitable from our point of view. Or, plants trick us with fruit and ornament into amplifying their evolutionary advantage.

What then has driven the laborious development of agriculture? After filling available geographical niches, the only way to expand is intensification. Agriculture essentially reduces the amount of land needed to support a person. The fruits of agriculture consequently support the human drive to multiply.

Draft animals were the first big advance. Draft animals did not reduce human toil. Peasants with animals work as hard as those without. Nor did draft animals drastically lift the productivity per worker, though an Iowan with a team could till far more than an Incan with a spade. Draft animals did increase the specific productivity of the land. Ruminants are the most successful symbiotic draft animals. Rarely competing with humans for food, they digest roughage and poor pasture, extracting energy from cellulose and properly managing nitrogen through the rumen’s flora. Still, draft animals take land. In some farming systems, one quarter or more of the land may be needed for oxen, horses, and other draft animals.

Chinese agriculture circa 1900 represents a high point of farm evolution. Without machines but using a thousand bioinformatic tricks, Chinese farmers reduced the amount of land needed to support a person to 100 square meters. Compare this space, about equal to a one-bedroom American apartment, to a few square kilometers for a hunter-gatherer. The difference is a factor of 104, or 10,000 times in intensification.

The ecological systems the farmers created, although often visually appealing, bear no resemblance to any natural ecosystem, if only because of great structural simplification. Equilibrium and resilience tend to be lost, and the system becomes unstable and difficult to manage. The wits and toil of about half the Chinese population are still employed to keep it going.

After the summit reached by the Chinese, farm evolution could continue only with a qualitative breakthrough. It came, like cooking, with the introduction of external energy, in this case fossil fuels. Starting around 1900 we tamed machines for the same purposes as draft animals, and started to synthesize chemicals rather than collect guano or manure. The two innovations, machines and chemicals, especially the latter, hugely increased yields.

After World War II, the automobile industry produced solid, cheap, dependable tractors. A tractor pulls as powerfully as 10 to 50 teams of oxen. Tractors proportionately increased the productivity of labor, without however substantially intensifying production. The machines did permit extension of cultivable land, and some gain in specific productivity came at the level of the farm, because the machines freed land that had produced feed for draft animals to produce for other purposes. In short, tractors released workers from the farms but did not grow much more corn per hectare.

The effect of chemicals, in contrast, fits the master trend of intensification perfectly. Fertilizers, most obviously, are intensifiers. They have always been used. The external energy of fossil fuels permitted their massive, economical, and convenient synthesis beginning about 1950.

The breakthroughs in external energy inputs allowed expansion and intensification of agriculture much faster than population growth, particularly in the United States. The difference created huge surplus capacity, especially for grains, and caused the invention and diffusion of the hamburger, a popular solution to the surplus.

In fact, as people get richer, they consume more calories and protein up to limits of satiety and taste. Given possible future diets and numbers, how much land can people spare for Nature? This is a question agronomist Paul Waggoner and I started asking about 10 years ago. The answer explains why forests will spread. Before giving the answer, let me broaden the context.


By the 1990s evidence accumulated that several major environmental indicators had passed an inflection point (Ausubel 1996). The most famous inflection is population growth rate.

Figure 1Reversal in total U.S. water use, per capita, per day.Sources of data: U.S. Bureau of the Census, Historical Statistics of the United States, Colonial Times to 1970 (Washington, D.C.: U.S. GPO, 1975). U.S. Bureau of the Census, Statistical Abstract of the United States: 1998, 118th edition(Washington, D.C., 1997).

The rate of growth of world population peaked at about 2 percent between 1965-1970. Fertility rates have continued to fall in most of the world the past 30 years.

Water use offers examples not only of slowing growth but of reversal. Both the withdrawal and consumption of water per capita peaked in the United States about 1980 (Figure 1), and the national total withdrawal also peaked in 1980 while consumption leveled. In the forest world, the reversal of deforestation had been discovered and named the Forest Transition (Mather et al. 1999). In recent decades some 50 countries have reported increases in the volume or area of their forests (UN ECE/FAO 2000).

A growing library of examples suggests that actually a Great Reversal in the exploitation of Nature has occurred (Ausubel 2001). Of course, we want to know how far the Great Reversal could extend. Could we envision a Great Restoration?

Visions necessarily entail targets or goals, whether for individuals, firms, or the planet. Goals provide orientation. They help actors to aspire and measure progress. In 1999, John Spears, a consultant to the World Bank, developed a preliminary, quantitative vision of world forests for the year 2050. The vision was exciting and worrisome: exciting because it could concert much work, worrisome because it accepted 200 million hectares more net deforestation, roughly the area of U.S. timberland. Yet, we all knew powerful reasons to spread forests: to increase habitat, sequester carbon, allow forests for traditional users, and keep wood products cheap and abundant.

Several of us, including Spears, agreed to start a process to create a vision worth realizing, one that restores Nature and merits investment. Together with the World Bank, the World Wildlife Fund, Council on Foreign Relations, and Rockefeller University joined in a Great Restoration project to develop an attractive and feasible vision for the world’s forests.

The Great Restoration project explored a range of questions:

–How widespread is the forest transition, the Reversal?

–What might be the size and character of the demand for wood products over the next 50 years?

–How much can higher growth rates of trees contribute to lessening demand for woodlands to be logged?

–What about “sacred groves”? Could, for example, new classifications of forested lands make a difference?

–What models of consent among different stakeholder groups are appropriate for a Restoration vision?

–What might be the spatial distribution of the Great Restoration?

–How can national and international law and institutions exert leverage?

As I will share with you later, we were able to create a feasible and attractive vision, with more forest in 2050 than today. Unsurprisingly, a key was the answer to the question, How much can farmers help by sparing land?


If farmers lift yields 1 percent per year and population grows by 2 percent per year while diet remains steady, land must be cleared for crops. If farmers lift yields 2 percent per year and population grows 1 percent per year, land is spared. For centuries, globally, land cropped expanded, and cropland per person even rose as people sought more proteins and calories. China’s brilliant yields were five times those of the crude farming of America and most of the rest of the world. But 50 years ago, rapidly lifting the specific productivity of land, the world’s farmers stopped plowing up Nature (Figure 2). During the past half-century, ratios of crops to land for the world’s major grains—corn, rice, soybean, and wheat—have climbed fast on all continents.

Figure 2. Reversal in area of land used to feed a person. After gradually increasing for centuries, the worldwide area of cropland per person began dropping steeply in about 1950, when yields per hectare began to climb. The square shows the area needed by the Iowa Master Corn Grower of 1999 to supply one person a year’s worth of calories. The dotted line shows how sustaining the lifting of average yields 2 percent per year extends the reversal. Sources of data: Food and Agriculture Organization of the United Nations, various Yearbooks. National Corn Growers Association, “National Corngrowers Association Announces 1999 Corn Yield Contest Winners, Hot Off the Cob,” (St. Louis, Mo., 15 December 1999). J.F. Richards, “Land Transformations,” in The Earth as Transformed by Human Action, B.L. Turner II et al., eds. (Cambridge University: Cambridge, U.K., 1990).

Per hectare, the global Food Index of the Food and Agriculture Organization of the UN, which reflects both quantity and quality of food, has risen 2.3 percent annually since 1960. In the United States in 1900 the protein or calories raised on one Iowa hectare fed four people for the year. By the year 2000 a hectare on the Iowa farm of Mr. Francis Childs could feed 80 people for the year, comparable to the most intensive Chinese agriculture. The Chinese, of course, kept lifting the comparison as they lifted cereal yields 3.3 percent per year between 1972 and 1995.

Since the middle of the twentieth century, such productivity gains have stabilized global cropland, and allowed many nations, including China, to shrink cropland. Meanwhile, growth in calories in the world’s food supply has continued to outpace population, especially in poor countries. A cluster of innovations including not only tractors and chemicals, but also seeds and irrigation, joined through timely information flows and better organized markets, raised the yields to feed billions more without clearing new fields.

High-yield agriculture need not tarnish the land. The key is precision agriculture. This approach to farming relies on technology and information to help the grower use precise amounts of inputs—fertilizer, pesticides, seed, and water—exactly where they are needed. I have mentioned two revolutions in agriculture in the twentieth century. First, the tractors of mechanical engineers saved the oats that horses ate. Then chemical engineers and plant breeders made more productive plants. The present agricultural revolution comes from information engineers. What do the past and future agricultural revolutions mean for land?

The agricultural production frontier remains open. On the same area, the average world farmer grows only about 20 percent of the corn of the top Iowa farmer, and the average Iowa farmer lags more than 30 years behind the state of the art of his most productive neighbor. On average the world corn farmer has been making the greatest annual percentage improvement. If during the next 60 to 70 years, the world farmer reaches the average yield of today’s U.S. corn grower, the 10 billion people then likely to live on Earth will need only half of today’s cropland. This will happen if farmers maintain on average the yearly 2 percent worldwide growth per hectare of the Food Index, slightly less than the record achieved since 1960, in other words if dynamics, social learning, continues as usual.  Even if the rate slows to half, an area the size of India, more than 300 million hectares, could revert from agriculture to woodland or other uses.

Importantly, a vegetarian diet of 3,000 primary calories per day halves the difficulty or doubles the land spared. I would also observe that eating from a salad bar is like taking a sport utility vehicle to a gasoline filling station. Living on crisp lettuce, which offers almost no protein or calories, demands many times the energy of a simple rice-and-beans vegan diet. We spend more than 100 calories of fossil energy to enter 1 calorie of winter lettuce in your mouth. It takes about 10 calories of fossil energy to deliver 1 calorie of beef. We need to be careful in accepting definitions of Green.

In fact, the unnecessarily high energy cost of modern agriculture should be reduced. The energy use can be split between machines and chemicals. In energy terms, they represent about equal inputs. Most of the work of the machines goes into tillage, whose main objective is to kill weeds. Low tillage techniques are, however, improving and spreading. The basis of low-tillage techniques is the use of herbicides to control weeds, while seeds are planted by injection into the soil.

Herbicides and pesticides that now operate on the principle of carpet-bombing are moving progressively to the hormonal and genetic level, and require less and less energy as the amounts of product needed are reduced. The big slice of energy taken for fertilizers, nitrogen in particular, could be produced by grains capable directly, or through symbiosis with bacteria, of fixing nitrogen from the atmosphere. Improved tractors, low tilling, targeted herbicides and pesticides, and an extended capacity for N fixation might reduce energy consumption in agriculture by an order of magnitude.

Lifting yields while minimizing environmental fallout, farmers can offer hundreds of millions of hectares for the Great Restoration (Waggoner and Ausubel 2001). The strategy, important for foresters too, is precision agriculture. Marchetti describes it as “more bits and fewer kilowatts.”


Farmers may no longer pose much threat to nature. What about lumberjacks? As with food, the area of land needed for wood is a multiple of yield and diet, or the intensity of use of wood products in the economy, as well as population and income. Let’s focus on industrial wood—logs cut for lumber, plywood, and pulp for paper.

Recurring to Reversal, consider the U.S. consumption of the four timber products: lumber, plywood and veneer, pulp products, and fuel. Between 1900 and 2000 the national use of timber products grew about 70 percent, but the preeminent feature is that the consumption of timber products rose far less than the rises in population and wealth might suggest (Wernick et al. 1998). At the end of the century, Americans numbered more than three and a half times as many as at the beginning, and an American’s average share of gross domestic product (GDP) had grown nearly fivefold. Had timber consumption risen in constant proportion to population, Americans would have consumed three and half times as much, not 70 percent more. Even more striking, if consumption had risen in proportion to economic activity or GDP, America would have consumed about 16 times as much timber each year in the 1990s as in 1900.

Industrial ecologists call a ratio of material to GDP its intensity of use. Because the annual percentage change of GDP is the sum of the changes in population and an individual’s share of GDP, a constant intensity of use means consumption is rising in step with the combined rise of population and personal GDP or income. A constant intensity of timber use would mean timber was playing the same role in the economy in 2000 as in 1990.

Practically, what changes the ratio of timber products to GDP? In the case of lumber, its replacement during the century by steel and concrete in applications from furniture and barrels to crossties and lath lowered the intensity of use. Living in the stock of existing houses and prolonging the life of timber products by protecting them from decay and fire lower it. In the case of pulp, more widespread literacy and the shift to a service economy raised the intensity of use in the early twentieth century. Thicker paper replaced thinner paper, and newspapers replaced oral gossip. More recently, thinner paper has again replaced thicker paper, and television has replaced newspapers, lowering the intensity of pulp per GDP.

Overall, history shows the extent of forests in the United States changed little in the twentieth century (Figure 3). Meanwhile, reversing hundreds of years of depletion, the volume of wood on American timberland has actually risen, by 36 percent since 1950. The main reason the forest has grown rather than shrunk is that on average a contemporary American annually consumes only half the timber for all uses as a counterpart in 1900. Meanwhile millers learned to get more product from the same tree, and foresters grew more wood per hectare. Already many areas initially cleared have regenerated, as evidenced by today’s large wooded areas in New England and the upper Great Lakes states.

Figure 3. Reversal and restoration of U.S. forests. Outer frame: U.S. forest land area, 1630-1997. Inset: U.S. forest volume, hardwoods and softwoods, 1952-1997. Sources of data: D.S. Powell, J.L. Faulkner, D.R. Darr, Z. Zhu, and D.W. MacCleery, Forest Resources of the United States, 1992, USDA Forest Service Report GTR-RM-234 (Fort Collins, Colo., USDA Forest Service, 1993). R.A. Sedjo, “Forests: Conflicting Signals,” in The True State of the Planet, edited by R. Bailey (New York: Free Press, 1995). W.B. Smith, J.L. Faulkner, and D.S. Powell, Forest Statistics of the United States, 1992, USDA Forest Service Report GTR-NC-168 (St. Paul, Minn., USDA Forest Service, 1994). W.B. Smith, 1997 RPA Assessment: The United States Forest Resource Current Situation (Washington, D.C.: USDA Forest Service, 1999).

In short, the wood “diet” required to nourish an economy is determined by the tastes and actions of consumers and by the efficiency with which millers transform virgin wood into useful products, and changing tastes and technological advances are already lightening pressure on forests. Concrete, steel, and plastics have replaced much of the wood once used in railroad ties, house walls, and flooring. Demand for lumber has become sluggish, and in the last decade world consumption of boards and plywood has actually declined. Even the appetite for “pulpwood”—logs that end as sheets of paper and board—has leveled.

Meanwhile, more efficient lumber and paper milling is already carving more value from the trees we cut. Because waste is costly, the best mills—operating under tight environmental regulations and the gaze of demanding shareholders—already make use of nearly the entire log. In the United States, for example, leftovers from lumber mills account for more than a third of the wood chips that are turned into pulp and paper; what is still left after that is burned for power. And recycling has helped close leaks in the paper cycle. In 1970, consumers recycled less than one-fifth of their paper; today the world average is double that.

The wood products industry has learned to increase its revenue while moderating its consumption of trees. Demand for industrial wood, now about 1.5 billion cubic meters per year, has risen only 1 percent annually since 1960, while the world economy has multiplied at nearly four times that rate. If millers improve their efficiency, manufacturers deliver higher value through the better engineering of wood products, and consumers recycle and replace more, in 2050 demand could be only about 2 billion cubic meters per year and thus permit reduction in the area of forests cut for lumber and paper.

The permit, as with agriculture, comes from lifting yield. The cubic meters of wood each hectare grows each year provide large leverage for change. Historically, forestry has been a classic primary industry. Like fishers and hunters, foresters for centuries hunted and fished out local resources and then moved on, returning only if trees regenerated on their own. Most of the world’s forests still deliver wood this way, with an average annual yield of perhaps 2 cubic meters of wood per hectare. If yield remains at that rate, by 2050 lumberjacks will regularly saw nearly half the world’s forests (Figure 4). That is a dismal vision—a chainsaw every other hectare, “Skinhead Earth.”

Figure 4. Present and projected land use and land cover. Today’s 2.4 billion hectares used for crops and industrial forests spread on “Skinhead Earth” to 2.9 while in the “Great Restoration” they contract to 1.5. Source: Victor and Ausubel 2000.

Lifting yields, however, will spare more forests. Raising average yields 2 percent per year would lift growth over 5 cubic meters per hectare by 2050 and shrink production forests to just about 12 percent of all woodlands—a Great Restoration (Victor and Ausubel 2001).

At likely planting rates, at least one billion cubic meters of wood—half the world’s supply—could come from plantations by the year 2050. Seminatural forests—for example, those that regenerate naturally but are thinned for higher yield—could supply most of the rest. Small-scale traditional “community forestry” could also deliver a small fraction of industrial wood. Such arrangements, in which forest dwellers, often indigenous peoples, earn revenue from commercial timber, can provide essential protection to woodlands and their inhabitants.

More than a fifth of the world’s virgin wood is already produced from forests with yields above 7 cubic meters per hectare. Plantations in Brazil, Chile, and New Zealand can sustain yearly growth of more than 20 cubic meters per hectare with pine trees. In Brazil eucalyptus—a hardwood good for some papers—delivers more than 40 cubic meters per hectare. In the Pacific Northwest and British Columbia, with plentiful rainfall, hybrid poplars deliver 50 cubic meters per hectare.

Environmentalists worry that industrial plantations will deplete nutrients and water in the soil and produce a vulnerable monoculture of trees where a rich diversity of species should prevail. Meanwhile, advocates for indigenous peoples, who have witnessed the harm caused by crude industrial logging of natural forests, warn that plantations will dislocate forest dwellers and upset local economies. Pressure from these groups helps explain why the best practices in plantation forestry now stress the protection of environmental quality and human rights. As with most innovations, achieving the promise of high-yield forestry will require feedback from a watchful public.

The main benefit of the new approach to forests will reside in the trees spared by more efficient forestry. An industry that draws from planted forests rather than cutting from the wild will disturb only one-fifth or less of the area for the same volume of wood. Instead of logging half the world’s forests, humanity can leave almost 90 percent of them minimally disturbed. And many new tree plantations are established on abandoned croplands, which are already abundant and accessible.


Because humans already number more than 6 billion and we are heading for 10 billion in the new century, we already have a Faustian bargain with technology. Having come this far with technology, we have no road back. If wheat farmers in India allow yields to fall back to the level of 1960, to sustain the present harvest they would need to clear nearly 50 million hectares, about the area of Spain.

Through further, precise intensification, farmers can be the best friends of the forest; alternatively they can plow through it. Technology can double and redouble farm yields and spare wide hectares of land for nature. I have confidence that farmers and their partners in the scientific community and elsewhere will meet the challenge of lifting yields per hectare close to 2 percent per year through the new century.

Freed and encouraged by the sparing of farmland, humanity can set a global goal of a spread in forest area of 10 percent, about 300 million hectares, by 2050. Furthermore, we should concentrate logging on about 10 percent of forestland. Behavior can moderate demand for wood products, and foresters can make trees that speedily meet that demand, minimizing the forest we disturb.

Social acceptance of the vision of the Great Restoration is key, both for farmers and for foresters. The global vision of a Great Restoration of forests that I have shared needs to be worked out in regional detail. Let’s begin in North America.

The essence of the strategy for foresters to achieve the Great Restoration is the same as that for farmers, more bits and fewer kilowatts. Call it precision forestry. Working precisely, we can spare farmland and spread forests.

Acknowledgments: Dale Langford, Cesare Marchetti, Perrin Meyer, David Victor, Paul Waggoner, and Iddo Wernick. This paper integrates work we have done together cited in the literature below.

Literature cited

AUSUBEL, J.H. 1996. Can technology spare the earth? American Scientist 84:166-178.

AUSUBEL, J.H. 2001. The great reversal: Nature’s chance to restore land and sea. Technology in Society 22:289-301.

MARCHETTI, C. 1979. On energy and agriculture: From hunting-gathering to landless farming. RR-79-10. International Institute for Applied Systems Analysis, Laxenburg, Austria.

MATHER, A.S., J. FAIRBAIRN, and C.L. NEEDLE. 1999. The course and drivers of the forest transition: The case of France. Journal of Rural Studies 15:650-690.

UN ECE/FAO. 2000. Forest resources of Europe, CIS, North America, Australia, Japan and New Zealand (industrialized temporate/boreal countries), contribution to the Global Forest Resources Assessment 2000. New York: United Nations.

VICTOR, D.G., and J.H. AUSUBEL. 2000. Restoring Forests. Foreign Affairs 79(6):127-144.

WAGGONER, P.E., and J.H. AUSUBEL. 2001. How much will feeding more and wealthier people encroach on forests? Population and Development Review 27(2):239-257.

WERNICK, I., P.E. WAGGONER, and J.H. AUSUBEL. 1998. Searching for leverage to conserve forests: The industrial ecology of wood products in the United States. Journal of Industrial Ecology 1(3):125-145.


Jesse Ausubel is director of the Program for the Human Environment, The Rockefeller University, New York City.