Question:     What is ecological footprinting?

Answer:     It is a technique that has begun to measure the ecological carrying capacity of Earth - to find out how many human beings the planet can carry without degrading its ecology and atmosphere beyond a specified limit.

Definitions:     According to two experts whose research OPT uses, Mathis Wackernagel and Jonathon Loh, "It is a non-monetised indicator of human pressure on the biosphere. For any population, its ecological footprint represents the biologically productive area required to produce the crops, meat, fish and wood consumed, to absorb the carbon dioxide emitted from fossil fuels burnt, and to give room for infrastructure used by that population." OPT Research Co-ordinator Andrew Ferguson defines eco-footprinting as "the process of determining the bioproductive area that a person (or a population) needs in order to sustain a specified lifestyle." WWF says an ecological footprint compares countries' resources with the Earth's biological capacity to regenerate them" or "a measure of humanity's use of renewable natural resources." Or, more specifically, "The ecological footprint represents the biologically productive land and water areas required to produce the resources consumed and assimilate the wastes generated by a given population using prevailing technology."

Question:     How does it work?

Answer:     In simple terms, there are two sides to ecological footprinting - supply and demand (of renewable resources). An ecological footprint = demand for (and impacts on) biological product, defined as the area (mostly land) that is needed for that product. The area needed was originally expressed as an area unit in ecological footprinting, but is now called a global hectare. Biological productivity (bioproductivity) or biocapacity = supply of biological product (biomass). The results are presented as broad conclusions, but the methodology is quite complex, involving 'equivalence factors' for example, to arrive at the most recent results.

Question:     Where does the data for eco-footprinting come from?

Answer:     Mainly from data published by the FAO (United Nations Food and Agriculture Organisation), the IEA (International Energy Agency) and the IPCC (Inter-governmental Panel on Climate Change). Also from studies in peer-reviewed science journals.

Question:     How does eco-footprinting help to explain population issues?

Answer:     Eco-footprinting indicates how much land (in global hectares) is needed to support a person's or population's lifestyle. In defence of continued population growth, for example, you cannot just say that the whole population of the world could stand up on the Isle of Wight. Each person needs food, fibres, energy and built infrastructure to support their lifestyle, and the amount of productive territory (technically, the biosphere, including land and fishing grounds, but excluding deserts and ice caps) needed to supply this lifestyle tends to increase as that lifestyle gets more comfortable. This demand on the biosphere is known as the ecological footprint. Just as a heavy human foot can distort or destroy a small patch of nature, the sum of human activities impacts on the whole biosphere.

Question:     What is a global hectare?

Answer:     A global hectare abbreviated to gha, although derived from the measurement of territory, refers to its biological productivity, not its size. (A real hectare is 2.47 acres.)

Question:     So what is biological productivity?

Answer:     The production of biological material, or the rate or yield of that production. It refers to the production of renewable biological resources, not resources such as oil, which is a fossil fuel created originally by biological processes but only usable once. (However, ecological footprinting does take into account the renewable resources needed to absorb the impact of fossil fuel use - which is the source of some controversy.) All life depends ultimately on plants photosynthesising their own tissues using sunlight. These plants can be eaten directly, or eaten by animals which are then eaten or used by humans. (Or sea plants can be eaten by fish, which are eaten by bigger fish, to produce food for humans.) Timber (effectively also the product of a plant) is used by humans - burnt for fuel, or used for building or manufacture. Fibres produced by plants can end up as clothes. Taken together, biological resources can be described as biomass.

Question:     Surely there is no uniform rate of production of these biological resources?

Answer:     Correct. Some types of vegetation are more productive than others. Croplands and Forests produce more plant material per hectare than Grazing land (pasture) and Fishing grounds (These four are separate categories of biological productivity for eco-footprinting purposes). In the case of pasture, for example, much of the photosynthesised energy embodied in the fodder is used by the metabolism of grazing animals, resulting in consumption of meat and dairy products that are an inefficient way of converting solar energy for human use.

Question:     Can you explain clearly how a global hectare measures this productivity?

Answer:     Imagine this example, set on a tiny planet which has only two countries (North Country and South Country, each with eight inhabitants), four hectares of cropland and four main types of crop: Green Grass (GG), Yellow Corn (YC), Red Apples (RA) and Blue Berries (BB). In one year, the planet produces 40 kilos of GG, 30 kilos of YC, 20 kilos of RA and 10 kilos of BB. These crops are gathered, mixed together to make 100 Average Brown Crop (AC), and allocated evenly across the four hectares. Now there are four global hectares of average biological productivity (of ABC) of 25 kilos each. That is the biological supply.

Question:     How is a global hectare used to measure demand - the footprint?

Answer:     On the same tiny planet, if North Country consumes 75 kilos of the 100 kilos of AC (average crop) each year its demand is a total 3 (of four) global hectares of average crop - a per capita (cropland) footprint of 3/8 = 0.375 gha. South Country consumes only 25 kilos, so its (cropland) footprint is one of four hectares. Per capita, that's 1/8, or a (cropland) footprint of 1/8 = 0.125 gha.

Question:     That's fairly simple. But some types of land are much more productive than others. How does eco-footprinting deal with that?

Answer:     A hectare of cropland, for example, will produce a lot more plant material than a hectare of of pasture. To account for these differences, eco-footprinting introduces an Equivalence Factor into the calculation. One hectare of real world cropland, for example, is calculated to be equivalent in productivity to only 2.11 theoretical global hectares, while one hectare of real world pasture is calculated to be equivalent in productivity to only 0.47 theoretical ghas.

Question:     What about double-counting - or half-counting? A forest could provide wood for paper (forest footprint) and at the same time absorb carbon dioxide (energy footprint) - how is that treated?

Answer:     Each area is counted only once, on both sides of the ecological balance sheet (footprint/biocapacity), even if it provides two or more ecological services at the same time.

Question:     In LPR 2002 the Earth's biologically productive space is assessed as 11.4 billion hectares, compared with 12.6 billion in LRP 2000 [earlier edition]. Why?

Answer:     When LPR 2000 was updated to the 2002 version, FAO [the international Food and Agriculture Organisation, the main data source] had changed some of its categorisations. Views have changed, for example, about the classification of failed crops. In LPR 2002, the defined cropland was up by 0.2 bn. ha. (billion hectares) compared with LPR 2000; grazing land down by 1.1 bn. ha., forest land up by 0.5 bn. ha., fishing grounds down by 0.9 bn. ha., and built-up land by 0.1 bn. ha. These changes are not significant in terms of the 'broad brush' overview that eco-footprinting provides.

Question:     The difference in footprint size, expressed in gha. (global hectares) is sometimes quite large. For example, for the UK the LPR 2002 footprints are given as follows (2000 figures in brackets): cropland 0.68 (1.03); grazing land 0.33 (0.69); forest 0.32 (0.36); fishing grounds 0.47 (0.05); carbon dioxide 2.99 (3.80); and built-up land 0.21 (0.37). Why?

Answer:     These changes arise from causes other than different data sets. The point to realise is that the area given in terms of LPR 2002 global hectares cannot be compared directly with areas given in LPR 2000 global hectares because different 'equivalence factors' are used. What can be compared are areas which are expressed in worldwide productivity terms, or local area terms (sometimes called 'national' areas). This can be demonstrated by dealing with the different land types in the UK, changing the figures into worldwide productivity terms, as in the following questions and answers.

Cropland:     if you convert the UK LPR 2000 figure of 1.03 global hectares (gha) to worldwide hectares (wwha.), by dividing it by the equivalence factor, you get 1.03 / 3.16 = 0.33 wwha. Doing the same for the 0.68 gha. of LPR 2002, you get 0.68 / 2.11 = 0.32 wwha., so there is little change here. It is mainly the equivalence factors that changed the gha. figures. These equivalence factors affect the footprint and the biocapacity equally, so the relationship between footprint and biocapacity does not change purely because equivalence factors are changed.

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Links to more detailed Questions and answers on eco-footprinting can be found via Sustainable populations by country.