Methodology for Determining Ecological Footprint

 

The basic procedure for the footprint methodology is to determine annual global productivity and assimilation capacity (biocapacity) of major land areas. Then, this biocapacity is compared to the demands placed on it by human consumption and waste production. Productive lands are aggregated as cropland, pasture, forest, fisheries, and built-up land. Built-up land is generally assumed to occupy former cropland, as this is the predominant settlement pattern in human history. The present footprint methodology holds that less than one quarter of the Earth's surface provides sufficiently concentrated biomass to be considered biologically productive—leaving out deep ocean areas, deserts, frozen tundra, and other less productive parts of nature. Biocapacity can change: both negatively, due to land alterations such as desertification; and positively, due to improvements in technology that result in higher yields.

Ecological footprints can be calculated using two basic approaches: component and compound. Component footprinting is a bottom-up approach consisting of calculating the ecological footprints of individual parts of a system and then adding them up. Compound footprinting, on the other hand, is a top-down approach using aggregate figures such as production, imports, and exports of agriculture, energy, and other commodities, usually for nations.

Using either component or compound methodology, human consumption and waste components of a footprint are attributed to the final point of utilization (where a product is used up and enters the waste stream), regardless of where the output is actually assimilated. For example, some waste products, such as carbon dioxide, may be assimilated well outside the boundaries of the place where they are actually emitted, either because the wastes are carried away from the point of use or because the wastes are generated at a remote production site.

The final footprint results from the comparison of global biocapacity to consumption and waste. High available biocapacity allows for more or larger footprints, and higher levels of consumption require more biologically productive land. Consumption beyond renewable levels of biocapacity requires the depletion of natural capital and is considered unsustainable if it draws resources down to the point at which they cannot regenerate.

Measuring the ecological footprint of energy is a particularly significant and complex challenge that can be addressed in a variety of ways. A primary question that arises concerns the type of energy that is being used. Highly renewable forms of energy production, such as wind and solar power, typically have footprints equivalent to the land area they occupy plus the materials embodied in the collection mechanism. At the other extreme, nuclear energy is inherently unsustainable both because the resources it utilizes are non-renewable and extremely toxic, and because the potential destruction from nuclear accidents produces a dramatic increase in footprint area. The current approach is to convert nuclear energy to the equivalent fossil fuel impact. The footprint of fossil fuels can be calculated as either the amount of land area that would be required to grow and harvest an equivalent amount of fuelwood, or as the amount of land area required to assimilate associated carbon dioxide emissions. The latter approach is the most typically used in footprint accounts.

Footprint calculations through the beginning of the twenty-first century have assumed optimistic yield factors for foods and forests (making them conservative) and have left unmeasured many of the impacts associated with pollution, water use, and habitat and species decline. Though improvements are being made in the methodology, the ecological footprint cannot be considered a definitive measurement of humanity's ecological impact without significant additions.

Footprinting provides a methodology to evaluate potential tradeoffs among alternative actions, designs, energy sources, policies and products. It can be used as a yardstick for measuring humanity's impact on the earth in terms of ecological sustainability. Research in the field has provided the stimulus and foundation for academics at universities throughout the world. The ecological footprint has informed discussions and debates from the global to local level in national governments, meetings of the United Nations, research institutes, and municipal sustainability initiatives.

Footprints change over time, as populations change, consumption patterns shift, and biocapacity increases or decreases. The changes allow humanity to see its progress toward sustainability, at a global, national, state, and local level.