What We Use and What We Have:
Ecological Footprint and Ecological Capacity

Dr. Mathis Wackernagel

The Footprint Measures Human Impact On Nature

Because people consume the products and services of nature, every one of us has an impact on our planet. This is not problematic as long as the human load stays within the ecological capacity of the biosphere. But does it?

The ‘ecological footprint’ concept has been designed to answer this question and estimate people’s impact. It does this by measuring how much nature people use today to sustain themselves. Ecological footprint calculations are based on two simple facts:

• We can keep track of most of the resources we consume and many of the wastes we generate; and
• Most of these resource and waste flows can be measured as a corresponding biologically productive area.

Thus, the ecological footprint of any defined population (from a single individual to a whole city or country) is expressed as the area of biologically productive land and water required exclusively to produce the resources consumed and to assimilate the wastes generated by that population, using prevailing technology. As people use resources from all over the world and affect far away places with their wastes, footprints sum up the extent of these ecological areas wherever they may be located on the planet.

The American Footprint …

Estimates for the year 1995, for example, which are based on the most recent publicly accessible United Nations statistics, show that the average American required approximately 24 acres (or 9.6 hectares) to provide for his or her consumption expressed in the common unit of ‘bioproductive space with world average productivity’. This space totals over 9 hectares of biologically productive land and 0.1 hectare of ecologically productive sea space. These 24 acres or 9.6 hectares correspond to 96,000m² (960 times 100 ms) or 24 football fields.

… Compared To The Available Eco-capacity

Dividing all the biologically productive land and sea on this planet by the number of people inhabiting it results in an average of 2.1 hectares (5.2 acres) existing per person in 1999. This capacity per capita is less than a quarter of what is necessary to accommodate the 9.6 hectares footprint of an average American. Of these 2.1 hectares per person, 1.6 are land based natural and managed ecosystems such as forests, pastures and arable land; 0.5 hectares are ecologically productive ocean areas most of which are located on continental shelves.

However, there is a slight complication. People should not use all the 2.1 hectares per capita since we are not alone on this planet. We share it with over 10 million other species – most of whom are excluded from the spaces we occupy so intensively for human purposes. For example, industrial agriculture calls ‘weed’ any species that is not exploitable, and for urbanization, much of the most fertile land is just paved over. How much of the bio-productive area should we leave relatively untouched for these other 10 million species? How much would be fair? How much would you feel is necessary to secure an ecologically stable world?

Having personally asked many people, I have met only a few who think we should leave less than one third of the eco-capacity for the many other species whom we typically exclude through our practices. To be even more generous to the human species and make sure that our analysis does not exaggerate the ecological scarcity of today, we follow the politically courageous, but ecologically insufficient suggestion by the Brundtland Report: Our Common Future (1987). Its authors invited the world community to protect 12% of the biologically productive space for preserving the other 10 million species with whom we share this planet. Using this conservative number, the available bio-productive space per person shrinks from 2.1 to just under 1.8 hectares.

Even though the average footprint of humanity is 5.5 acres per person, it still exceeds the eco-capacity of the biosphere. If we put aside a meager 12% for the other species, then we exceed the Earth’s capacity by 20%. Ecologists call this transgression of the Earth’s carrying capacity ‘overshoot.’ In other words, humanity consumes more than what nature can regenerate and is eating up the globe’s stock of natural capital. The sustainability challenge then becomes: “how can each of us have a satisfying life within the average of 1.8 hectares per person or less?” This is probably the most significant question we face in research, business and politics.

How Is The Footprint Calculated?

The ecological footprint is an accounting tool that aggregates human impact on the biosphere into one number: the bioproductive space occupied exclusively by a given human activity. It does this by adding up human uses of ecological services in a way that is consistent with thermodynamic and ecological principles. For example, it recognizes the ecological interactions of ecological functions by only adding up mutually exclusive functions of nature such as food production or CO₂ sequestration. Or it incorporates thermodynamic thinking by distinguishing between energy qualities and differentiating between abilities of ecological spaces to produce biomass. Since the method builds on the assumption that the limiting factor for human life on this planet is the regenerative capacity of the biosphere, the accounts capture human use of nature in as far as it impacts this capacity. This means that the use of non-renewable resources such as oil or copper ores is incorporated into footprint assessments to the extent that it limits nature’s integrity and productivity.

Among a variety of compatible methods to calculate people’s footprints, there are two basic approaches – compound footprinting or component-based footprinting. Depending on the size of the population, we can choose between the two or use a hybrid of both to get the most accurate and useful results.

Compound Footprinting

The most robust and comprehensive approach is ‘compound footprinting.’ Applied at the national level, it traces all the resources a nation consumes and the waste it emits. The nation’s consumption is calculated by adding imports to, and subtracting exports from, the domestic production. To put it in mathematical terms: consumption = production - exports + imports. This balance is calculated in approximately 60 categories, such as cereals, timber, and tubers. Each category includes both primary resources (such as raw timber or milk) and manufactured products that are derived from them (such as paper or cheese). Resource use is expressed in units of space by dividing the total amount consumed by the respective ecological resource productivity and the total amount of waste by the corresponding capacity to absorb waste.

To increase the consistency and robustness of the results, each component is screened for double counting. Since double counting could exaggerate the footprint, secondary ecological functions that are accommodated on the same space are not added to the footprint. For example, honey produced from a pasture for dairy cattle would not add to the footprint. Neither would the collection of mushrooms in a forest credited with timber production or CO₂ absorption.

To provide results in comparable units of measure, all components are adjusted for their biological productivities. This means that land with higher than average productivities would appear larger in footprint accounts. The same is done on the capacity side when a region or nation’s ecological capacity to accommodate footprints is analyzed.

Now all these adjusted components can be added for a total footprint. The analysis provides both a number for the overall footprint as well as for the overall biological capacity. If the footprint exceeds the capacity, this means that the region has an ecological deficit. If the per person footprint exceeds the global average, the magnitude of the person’s contribution to the global ecological deficit is clarified.

The advantage of compound footprinting is that it automatically captures many indirect effects of consumption, which are hard to measure, because this approach does not require knowing what each consumed resource is used for. For example, it is irrelevant for the accounting whether the consumed energy powers vehicles, heats homes, produces cars sold in the country, or is merely wasted. Since there are robust statistics on overall energy consumption but much less accurate data on exact use of the energy, the overall assessment of compound footprinting makes the accounts more reliable.

Component-Based Footprinting and Combinations

The second accounting approach, ‘Component-based footprinting,’ adds up the footprint of each category of consumption. Even though this approach is more instructive and more flexible for calculating footprints of individuals or organizations, it is more prone to errors since reliable data for assessing indirect consumption components, such as embodied energy and materials in goods and services, is scarce. Still, sometimes sufficient data from life cycle analyses is available to develop reasonably good estimates at the product level.

For the calculations of footprints for populations smaller than a nation, but larger than a household, the most effective method is a hybrid of these two approaches. For regions or municipalities, their footprint is assessed by extrapolating from the national footprint using the relative differences in the consumption pattern of the region and the nation. Both the individual and the regional footprint assessments are made more accurate by calibrating them with the national accounts.

A Tool For Moving Toward Sustainability

To move towards sustainability requires improving many people’s quality of life while reducing humanity’s footprint. Impossible? No. Three complementary strategies can reduce footprints without compromising our quality of life. We can:

• Improve the bio-productivity of nature sustainably. We can extend the bioproductive areas through reforestation or soil conservation. Also, we can increase harvests and services per hectare. Examples include: permaculture, agricultural infrastructure such as terraces on mountain slopes or careful irrigation, reforestation or installing solar panels on unutilized roof areas;
• Use the harvested resources better by using less input to produce the same output, as in energy efficient lamps or heat pumps, recycling, or climate adapted architecture; and
• Consume less by consuming less per person and by reducing population in future generations. For example we can avoid car use or the purchase of disposable products -- at the same time we will save money and may afford ourselves more leisure time. This simpler lifestyle may also put less strain on our health and help us enjoy more the quality of our lives. In the long term, reducing consumption and waste per capita can succeed in reducing the total human footprint only IF the human population does not continue to increase.

Remember, all these strategies have to be used in a way that both improves quality of life and reduces the size of humanity’s footprint.

Existing Footprint Applications

By providing clear ways to assess potential tradeoffs, the ecological footprint becomes a yard stick for measuring the ecological bottom-line of sustainability – a precondition for satisfying lives. The tool has provided the stimulus and foundation for many courses and thesis projects at universities all over the world. More importantly, it has informed discussions and debates from the global level to the local scale by national governments, UN meetings, research institutes, and municipal green plan initiatives to name a few. Global and national studies have compared countries’ overall consumption to their eco-capacities or analyzed the ecological capacity embodied in trade. Municipal footprints have been computed and sustainability strategies evaluated with the footprint tool. At the household scale, the individual impacts have been assessed with a variety of calculators, including software programs explicitly designed for adoption in school curricula. The ecological demands of specific products or the cumulative effects of consumer items have also been compared using the footprint method.

Conclusion

Ecological footprint accounts can help policy planners assess a population’s ecological impact and compare this impact to nature’s capacity to regenerate. In other words, footprints contrast human load with nature’s carrying capacity. These analyses give us a benchmark for today’s ecological performance, identify the challenges for lightening people’s ecological load, and allow us, as members of society and managers of the public and private sectors, to document gains as a country, region, city or company moves toward sustainability. In this way, the ecological footprint becomes a tool for weighing the merits of potential policies and developing effective strategies and scenarios for a sustainable future.

Source: Mathis Wackernagel, Redefining Progress.

For more background information, applications and links to other projects, visit the web site of the Indicators Programme of Redefining Progress, which contains descriptions and resources of footprint projects.