Toward a stewardship of the Global Commons:

engaging “my neighbor” in the issue of sustainability


By members of the Critical Issues Committee, Geological Society of America

Part VI


A. R. Palmer, Institute of Cambrian Studies, Boulder, CO

Every one of us requires a finite area of Earth’s surface to support his/her existence. This is our Ecological Footprint (Wackernagel and Rees, 1996). Its principal components are our food footprint, our wood products footprint, and our degraded land footprint.

If I eat potatoes, in the course of a year I consume a measurable quantity of potatoes. There is thus an area of potato production somewhere in the world that is dedicated solely to me for my annual consumption of potatoes. Ditto for every other terrestrial food product I consume. That’s my food footprint. This footprint is not fixed in size. I can change it by changing my eating habits – beef carries a bigger footprint than chicken.

My use of printer paper, the packaging of the products I buy, the magazines and newspapers I read, the wood in my furniture and my home, and the firewood I consume if I have a fireplace, constitute my personal wood products footprint. This puts real demands on an area of the global forest that must be dedicated solely to me. However, this footprint must also include my share of the wood products in the infrastructure that supports me. I can change the overall footprint only a bit with decisions about my personal consumption.

My degraded land footprint is comprised of the area under my house and driveway. For others, it maybe a part of the shared area under our apartment buildings and adjacent parking lots. We also share a part of the land under our city streets, businesses and public buildings and under the industrial infrastructure that supports us, as well as a part of the land beneath our highways, railroads, airports and garbage dumps. I can’t do too much to change this, which is a reflection of our culture.

It is possible to calculate a semi-quantitative estimate of our food, wood products and degraded land footprints and thus a measure of our minimal land-use needs at current levels of consumption. If this level of "need", when projected to the global population, exceeds the available land areas of earth, we have a problem. On the other side of this coin, if we decide on the desirability of a particular level of consumption, we can get a rough idea of how many of us can be supported at this level by the land resources at our disposal – i.e., the carrying capacity of the land.

In addition to the "accountable" elements of our footprint cited below, there are other less tangible footprint elements represented by our use of fossil energy and water. Approximately 50% of the carbon dioxide we generate burning fossil fuels cannot be accommodated by existing terrestrial or oceanic sinks. If we had to create new forest to serve as a carbon dioxide sink, to keep the human contribution to atmospheric carbon dioxide from increasing, we would need to more than double the world’s area of forest – an improbable solution. And warming oceans will hold even less carbon dioxide than they do now. It appears that the human component of carbon dioxide buildup in the atmosphere will remain with us until we stop burning fossil fuels. The footprint effects of water use are more subtle. When the lower reaches of the Yellow and Colorado rivers, for example, run dry because of upstream human water use, this seriously impacts downstream ecosystems in ways that are difficult to measure.

I have calculated the accountable components of the per-capita Ecological Footprint for the United States (Palmer, 1999). Our food footprint, using figures from the U.S. Department of Agriculture and related sources is about 1.5 acres. In simple terms, this is obtained by determining yields in pounds per acre for each foodstuff. That number is easily converted to acres per pound. Data on our per-capita consumption of each foodstuff in pounds is also available. The per-capita area required for each foodstuff is then calculated by multiplying these two figures. The sum of the resulting areas is our per-capita food footprint. Similarly, our annual U. S. per-capita demand on the world’s forest for all wood products needs is estimated to be 0.04 to 0.05 acres. This sounds trivial, but that area cannot be reused until it has regrown. On average, this takes about 40 years. Thus the estimated area of forest that must be dedicated to each one of us to sustain our present level of wood products consumption – our wood products footprint -- is about 1.6 acres (40 × 0.04 acres). Our U. S. per-capita degraded land footprint is estimated to be about 0.4 acre. Therefore, the total ecological footprint for the average American is a minimum of about 3.5 acres.

Lets put this in perspective. Earth has about 22 billion acres of ecologically productive land. This is comprised of about 3.3 billion acres of arable and crop land, 8.4 billion acres of pasture land, and 10.1 billion acres of forest land. Not all of the arable land is of high quality, and improving agricultural productivity by use of fertilizers and insecticides, or shifting to monocultural forestry, affects ecosystems in other, often deleterious, ways. Expansion of land use in any of those categories can only be done at the expense of one of the other categories, and development of the land for human structures of all kinds competes for this same area. Not only that, but we have to share this land with the other organisms on Earth who might not be able to tolerate our land use ‘improvement’ measures, or to survive as a group as environmental fragmentation becomes extensive.

If we maintain our current footprint and the human population of 2050 (estimated at 9 billion) reaches consumption levels similar to ours, which is a practical goal for the developing world, humanity would need 13.5 billion acres of land for food production and 14.4 billion acres for wood products on a steady-state basis to be sustainable, and we would have degraded about 3.6 billion acres for human structures. For humans alone, excluding the needs of other organisms, there is not that much land available simply by considering these three computable sorts of personal footprints!

Furthermore, the food footprint calculations cited above used U.S. yields, which are significantly higher than average global yields. If global yields were used in those calculations, our food footprints would be closer to 3 acres. Earth’s carrying capacity for a population with 3-acre food footprints might be no more than about 4 billion people (12 billion acres of arable, crop and pasture land ÷ 3). Each year more of our most productive farmland is buried under human structures, and both good and marginal farmland becomes unusable due to poor farming practices, so even the estimate of a sustainable carrying capacity of 4 billion people eating and living as we do may be high.

The simple calculations cited above should raise some warning flags that humanity already has a problem with the demands we make on Earth. And we seem to be continuing our present course unabated! Refinement of footprint and carrying capacity figures should be an ongoing part of the process of evaluating and monitoring the sustainability of the human enterprise.

DEMONSTRATION 1.   Have students estimate their annual consumption, in pounds, of various non-meat food items that they eat most often (beans, corn, potatoes, apples, etc.) – for meats, see Demonstration 2. On the Web there are data about U.S. food production where yields for most common agricultural products can be calculated in pounds/acre (sometimes with a little clever manipulation), and these figures can then be converted to acres/pound.. Multiplying the acres/pound figure by the student’s personal annual consumption in pounds for each foodstuff gives the area of the Earth dedicated to each individual for consumption of that food item. The Web also has tables of data on U.S. annual per capita consumption of various foodstuffs in pounds. The student can then compare her or his own footprint with the U.S. footprint for the same product and begin a discussion about whatever differences are found. The relevant websites are: and

DEMONSTRATION 2.   Do a similar exercise to Demonstration 1 but regarding the beef footprint, using the following data: Each beef animal on average needs 10 acres of pasture; when the animal goes to a feedlot, it consumes grain equivalent to 0.4 acre of a grainfield to reach the desired slaughter weight of 1,200 pounds. About half of that weight returns to the supermarket as the beef that we buy. Thus, 600 pounds of beef at the supermarket had a footprint of about 10.4 acres. What is the footprint of 1 pound? What is the per capita level of beef consumption, in pounds, in the U.S.? What is the student’s annual consumption of beef in pounds? Multiply the annual consumption in pounds by the footprint for one pound to obtain a beef footprint. Compare the two beef footprints, and also compare them with the footprints of the agricultural products from Demonstration 1. Develop a general discussion of ways in which the food footprint can be used to evaluate the impact that we make on earth just from our eating habits. How might the food footprint be used to evaluate carrying capacity?

DEMONSTRATION 3.   Our footprints directly impact land areas that were balanced parts of the natural ecosystem prior to the advent of human activities. Have students consider what is lost or disrupted, versus what is gained, by conversion of former forests, temperate grasslands (savannah), or semi-arid prairie to human agricultural use or human habitations. How might we determine when ecosystem losses outweigh human gains?

References Cited

Palmer, A. R., 1999, Ecological Footprints: Evaluating Sustainability: Environmental Geosciences,   v. 6, p. 200-204.

Wackernagel, M., and Rees, W., 1996, Our Ecological Footprint: Reducing Human impact on the   earth: Philadelphia, PA, New Society Publishers, 160 p.

For a current discussion of Ecological Footprints with most of the important literature citations, check the March 2000 issue of the journal Ecological Economics (v. 32, no. 3, pp. 341-394),which can be found in many larger university libraries.

Return to Introduction
Guidelines to Sustainability Literacy
Part I: Stewardship of the Commons
Part II: Understanding Deep Time
Part III: Doubling Time Part IV: Sustainability and Resources
Part V: The Connectedness of Everything
Part VI: Ecological Footprint and Carrying Capacity
Part VII: Spaceship Earth: There's No Place Left to Go
Part VIII: Part of the Global Ecosystem

Part IX: We Live in a World of Change
Part X: What Do We Mean by Sustainable World?
Part XI: Cultural Context of Sustainability
Part XII: We Have The Option of Choice

INVITATION BASIN is a community project actively seeking public participation. We appreciate all feedback and welcome comments, suggestions and contributions. To find out more about how you can be involved, click here.

BASIN is supported by the US EPA, the City of Boulder, WASH, BCWI and BCN
Home | Site Map | Glossary | Bibliography | Contributors
About BASIN | Attribution | Feedback | Search