How many people can the earth support?

Part Two. Ecological Footprints

(A) Introduction

The first comprehensive publication on ecological footprints (EF) was that by Mathis Wackernagel and William E. Rees (1996) “ Our Ecological footprint: Reducing Human Impact on the Earth”.

They defined the Ecological Footprint as follows:

“The Ecological Footprint of a specified population or economy can be defined as the area of ecologically productive land (and water) in various classes – cropland, pasture, forests, etc. – that would be required on a continuous basis

a) to provide all the energy/material resources consumed, and

b) to absorb all the wastes discharged by that population with prevailing technology, wherever on Earth that land is located ”.

“The thinking behind ecological footprint analysis builds on the concept of carrying capacity – the ability of the earth to support life”, and “in essence, the ecological footprint is a simple accounting tool that adds up human impacts (or use of ecological services) in a way that is consistent with thermodynamic and ecological principles” (1) .

Before I go any further, I should point out that ecological footprint analysis , although formally a “simple accounting tool” is actually an extremely time consuming, complicated and technical business, involving detailed research in several different fields and the construction of large spread sheets of data. Moreover, methods and estimates are continually being improved, which can be bewildering to any tyro attempting to understand EF using publications from different dates. I will give an example of changing estimates later when we consider what are called ‘equivalence factors'.

We will only touch on the main features of EF in this essay.

The basic idea of ecological footprints then, is to convert human impacts on the environment into land (and water) areas. Two examples illustrate the idea.

1) Cereal Foods. Man grows these and other foods. They occupy a certain total land area. If we divide this land area by the total number of people, we get a per capita land area.

2) CO₂ emissions. We may calculate the area of forest needed to sequester the carbon dioxide produced and thus avoid global warming.

For any population, if we could convert all components of man's impacts to land and water areas, giving us a complete inventory of man's impact, we could then add up all the areas to give us the total area required to support that population. In so far as the actual area occupied by the population is smaller than this total area, the difference is an indicator of the extent that the actual area is insufficient to support the population at its current standard of living.

“Current standard of living”. It is important to specify this. The average citizen of the USA eats more food and makes use of a far greater quantity of fossil fuels (e.g. automobile fuel) than the average citizen of India , and so has a greater impact on the environment than the average Indian. Footprint analysis then, takes into account the variation of standard of living between countries.

Now man's impact on the earth consists of two parts, the resources used, and the waste flows produced, as is illustrated by the two examples given earlier. The underlying assumption in ecological footprint analysis is that both these components can be adequately expressed in terms of physical land and water area. In practice, however, analyses have been incomplete for two reasons.

1. While exploitation of oceans and seas is included in analyses, fresh water areas have until very recently either not been accounted for, or only partly accounted for. For example, in the WWF's Living Planet Reports (6) , which will be discussed in later sections, the 2000 report ignores use of freshwater areas, while the new 2002 report does incorporate catches of food from freshwater.
2. Contamination of land and water has not generally been included in footprint analyses (acid rain; toxic materials such as plutonium, mercury, CFCs DDT and PCBs).

Footprint accounts will if anything therefore, under-estimate man's total impact on the environment. Other reasons why footprint analysis underestimates human impact are:

• Where more than one estimate is available, and there is real doubt, the more conservative estimate is chosen.
• ‘Double counting' is avoided: each area is counted only once, even if the area provides two or more ecological services. For example, consumer products like leather goods are the by-products of another industry, beef production. So only the primary land requirement – the grazing and grain lands required for feeding cattle is included in the footprint analysis.
• Analyses ignore long term environmental effects – they are based on current practices, which are often unsustainable. For example, current agricultural yields frequently depend upon agricultural practices which, causing soil erosion and other problems, will reduce yields in the future.

If we are to convert man's impact into land areas, we have to distinguish various types of land. The reason is that different land types are used for different purposes – e.g. arable land and pasture land, and different types of land have different productivities (see later). To these land types productive sea space is usually added. If we leave out non-productive areas that do not contribute directly to mans livelihood (icecaps, deserts), this gives us the following area types :

1. Crop land. In many accounts, this category is referred to as arable land – land primarily used for the staple grain crops like maize. But ecological footprint analysis usually now includes other crops like vegetables, fruit, crops grown for fibres, tobacco etc., so crop land is a better term to use.
2. Pasture land - used for grazing livestock.
3. Forested land - yielding timber products.
4. Productive sea space – quantitatively, most marine life is concentrated near or fairly near land. In fact the eight per cent of ocean area concentrated along continental coasts provides over 95 per cent of the marine catch. As already mentioned, the Living Planet Report 2002 includes freshwater areas.
5. Built on land. Built on land is biologically unproductive, however since it was originally highly productive arable land, it is potentially productive.
6. Energy land – most commonly the forested area which needs to be set aside to sequester CO₂ from fossil fuel combustion.
7. The pristine area needed to preserve biodiversity. Usually this is taken to be 12 per cent of biologically productive land (a figure rather arbitrarily suggested by the Brundtland Commission, and considered far too small by some ecologists).

Sometimes an extra land type is specified – gardens. Now these area types are mutually exclusive. However, forests as ordinarily understood contribute to three of the above types – 3, 6 and 7. So for accounting purposes forests must be divided between these three categories: forest areas for forest products, forest areas contributing to energy land and forest areas as a major component of biodiversity land.

Finally, this essay concerns the eco-footprinting analysis of nations and the whole world. Other branches of footprinting studies that concern individual cities, particular utilities like a power station, or individual people, will not be covered by this essay.

(B) The accounting method

( i ) Some basic principles

This account is mainly based on references 1 to 3 given at the end of this article.

Fundamental to the EF method is the idea of determining the area of land/water in each area type that is used per capita by the population of a given region or country.

To determine the per capita requirement requires three things:

1. The total consumption of the country or region by weight for each item. This is estimated using quantity produced, that is the assumption is made that production quantity is an adequate measure of consumption quantity. Since there will probably be exports and imports, a “trade –corrected consumption” often termed the “apparent consumption” is calculated : home production + imports - exports. Now the assumption of the production - consumption equivalence raises a problem. Production has two components – the waste associated with production, and the final consumable product, and these are not distinguishable in the apparent consumption value. This can lead to anomalies between countries. For example, consumption patterns in Ireland and the United Kingdom may be similar. Now Ireland has a much smaller population than the UK , but agriculture makes a significantly greater contribution to the economy that it does in the United Kingdom . Ireland then is charged with a relatively large footprint corresponding to waste generated when producing food for export. No official data exists to correct this error.

1. The productivity per hectare for each item; the productivity used is world average productivity. This has two advantages. First, it is then not necessary to trace all the sources of trade goods and waste sinks or determine the assimilation capacities of the corresponding assimilation areas, indeed this might not be possible anyway. Second, using a common base productivity makes it easier to make comparisons among countries and comparisons of individual country yields with global yields. For an answer to critics of the idea of using world productivity see Ferguson (4) .

1. The population size.

Then:

Total consumption of area ÷ human population size = per capita consumption.

Per capita consumption ÷ world average productivity = area requirement per capita.

An example concerns paper use by Canadians. This is based on example 2, page 81, of reference 2.

From the total Canadian paper use per year and the population size it was concluded that the per capita consumption of paper was 244 kg per year. In addition to the recycled paper that enters the process, the production of each metric ton of paper in Canada requires 1.8m³ of wood.

Now 1 metric ton = 1,000 kg.

So 1000 kg paper = 1.8m³ of pulp wood

Therefore 244 kg paper = 1.8 ÷ 1000 × 244 = 0.4392 m³ wood.

So per capita annual consumption = 0.4392 m³ wood.

Worldwide wood productivity was taken to be 2.3m³ per hectare per year.

So per capita ecological footprint for paper = 0.4392 ÷ 2.3 = 0.1909 ha of forest.

For consumption analyses, consumption is divided into the categories:

1. food
2. housing
3. transportation
4. consumer goods
5. services

Usually these categories are subdivided. For example, food divided into meat, dairy produce, marine life, cereals, fruit and vegetables. And these component categories are subdivided e.g. dairy produce divided into milk, cheese, butter, eggs.

For a full consumption analysis and for each consumption item, it is necessary to include all the resources that go into the production, use and disposal.

It is especially important to analyse energy consumption, for, as it turns out, the energy land footprint is the largest component of the total footprint in the affluence besotted developed world (in contrast to developing countries, apart from major oil producing countries where the energy land footprint is again often the largest component). Energy is recorded in Gigajoules. One Gigajoule = 1 ×10⁹ joules.

It is here that we meet the term “ embodied ” energy. With manufactured goods this is the energy used to manufacture, transport, use and dispose of these goods. We need here, for a start, to consider the materials from which these goods are made. Now with material extracted from ores, the amount of energy used in extraction obviously varies with the concentration of the material concerned. But on top of this consideration is the fact that some materials are far more energy- intensive to produce than others. Ironically, aluminium, an abundant substance, has one of the highest embodied energies. And aluminium smelting accounts for about one per cent of all world energy use. It is clearly a very complicated matter to try to fully account for embodied energy, and accounts tend consequently to be simplified.

Now materials used in manufactured goods contribute to man's footprint not only through the embodied energy, but also by the diminution of non-renewable resources, the amount of land used during extraction and for spoil heaps, and the pollution of land areas. In fact, when calculating an ecological footprint for materials, this direct land use has often been ignored, letting embodied energy represent the full set of impacts. So such material footprint estimates will obviously be on the conservative side.

The idea of embodied energy is also used in dealing with the energy implications of fresh water provision to industry and households. Here the embodied energy is the energy needed to treat, pipe, supply, and, where applicable, heat the water. Thus for example, one UK Water Utility Company provided data which showed that each megalitre (1 million litres) of water delivered results in the emission of around 370kg of CO₂ . Now it is calculated that 0.00019 ha is the area of forested land needed to sequester one kilogram of CO₂ . Then in terms of embodied energy, the ecological footprint of water is 370 × 0.00019 × 1.17 = 0.08 ha. Where does the figure 1.17 come from? This is the ‘equivalence' factor – see the following sub-section (ii) (note also that this example comes from Chambers et al - reference ( i ) page 99 - in which the equivalence factor used was 1.17 as shown in the table in this sub-section).

Energy from fossil fuels, so important to the world economy, must be accounted for in terms of land areas. The accounting method that has usually been used depends on estimating CO₂ emissions from fossil fuel combustion, and then estimating the extent this CO₂ can be absorbed by forests, thus translating fuel consumption to areas of land occupied by forests: Trees, like other green plants, absorb CO₂ in the process of photosynthesis, but emit CO₂ in the process of respiration. In so far as the absorbed CO₂ becomes a component of the tree's woody structure, trees can be net absorbers of carbon dioxide. What is calculated then, is the area of land needed today to sequester the CO₂. It has generally in the past been accepted that one hectare of average forest can accumulate about 1.8 tonnes of carbon per hectare per year. The corollary of this is that one hectare of forest can annually sequester the CO₂ emissions generated by the consumption of 100 gigajoules of fossil fuel (this is called the energy/land ratio).

According to Andrew Ferguson of the Optimum Population Trust (personal communication), these figures have been recently revised. It is now thought that one hectare of average forest can accumulate only about 0.95 tonnes of carbon per hectare per year rather than 1.8 tonnes as thought earlier, the equivalent of an annual sequestration of CO₂ emissions generated by the consumption of 73 gigajoules of fossil fuel. According to Ferguson , the change is partly through improved methods of estimation, but also because the earlier estimate was made ignoring the fact that the oceans absorb a considerable amount of CO₂ .

Now there has been considerable study of the extent that forests of different type (mature, new growth) and different location (boreal, temperate, tropical ) are net absorbers or net emitters of CO₂, and sometimes the results have been conflicting. Furthermore, while CO₂ is stored in the wood of trees, that storage is not permanent, since when trees die and decay, or are chopped down and burnt, the CO₂ is released back into the atmosphere. An additional complication is that as much or more CO₂ is actually stored in the soils of forests than in the trees themselves. When trees are removed and the soil used for agriculture - a common practice today - or new forest planting, this causes the release of a large amount of CO₂ from the soil. Furthermore, CO₂ is not only sequestered in forest soils, it is also sequestered in the soils of other habitats including arable land; how such soils are managed makes an appreciable difference to the extent these soils can sequester or release CO₂ . Afforestation can increase global storage, but if global emissions continue to remain high, the area of land that would eventually be required for the forests would exceed the land area that could be assigned to forests. Not surprisingly then, many people consider that carbon sequestration is of doubtful value for dealing with the energy component of footprints.

An alternative method of dealing with the energy footprint has therefore been suggested. This is based on renewable energy. There would be several components – fuel crop biomass (which would require a large allocation of land), wind farms, photovoltaics, etc. Ferguson (5) argues that using an appropriate mix of renewable energy sources could give an energy/land ratio similar to that for the carbon sequestration method. Numerous ecofootprint practitioners are now investigating the renewable energy approach.

(ii) Determining the total ecological footprint of a region or country and comparing it with the actual capacity of the same region or country

Having determined the ecological footprint in each area type, these values need to be added up to obtain the total footprint of the region or nation concerned . However, a correction to the area footprints must first be applied. This is because the idea is to present the result in terms of global average bioproductivity : different area types have different productivities, for example, arable land is much more productive than pasture land. So the footprint of each area type is adjusted through multiplying by what is termed an equivalence factor to express the footprint in units of area with global average bioproductivity. The resulting units are now usually referred to as ‘global hectares' gha , although in the Living Planet Report 2000 they are referred to as ‘area units'.

The following table shows equivalence factors given in a) Chambers et al (1) in connection with a 1995 study of Costa Rica, b) WWF (2000) and c)WWF (2002) (6) . The purpose of giving these three different sets of estimates is to illustrate the point made at the beginning of the essay, namely estimates are continually being refined.

We see here that forest land for forest products and forest for energy are given the same values. This is because while area types must be mutually exclusive, these two notional forest areas have identical productivity. It might seem strange that built up area is given a high equivalence factor, and actually the same as the area type with the highest productivity, namely arable land, since built up land is not productive of any crop (unless you include roof-top gardens). The rationale given is that the building of settlements has been and is, mainly on arable land. However, since eco-footprinting concerns the here and now rather than what happened in the past, I wonder if this is really valid. Now it is argued that built up land must be included in the footprint for if it were excluded, then any increase in a country's built up area at the expense of productive land, to build a road or airport for example, would not result in an increase in its footprint. As Andrew Ferguson (10) observes however, it would be best to deal with this problem directly, by taking account of the amount of arable land which is lost to building, thereby reducing total arable land area, rather than ascribing a mythical ‘biocapacity' to built-up land.

Earlier I used Canadian paper consumption as an example of footprint determination.

The per capita footprint was 0.1909 ha. The table above gives the WWF's 2002 forest equivalence factor as 1.35. Applying this to the paper footprint to express the footprint in terms of global average bioproductivity, one gets 0.1909 × 1.35 = 0.2577 global hectares.

The total ecological footprint is a conservative estimate of the amount of land that the population of the given region or country needs currently to support itself. This may be compared with the biocapacity that actually exists in the region or country, so as to determine whether or not there is a land deficit or surplus (biological capacity, or biocapacity, is defined in the Living Planet Report 2000 as the total biological production capacity per year of a biologically productive space, for example inside a country. ‘Biologically productive space' is defined as the land and water area that is biologically productive. It is land or water with significant photosynthetic activity. Marginal areas with patchy vegetation and non-productive areas are not included). Like footprints, biocapacity is expressed in global hectares.

To work out the biocapacity a further adjustment has to be made. We saw earlier that the basic footprint calculations are made using world average productivity figures. Now productivity for any given area type varies greatly between nations, and this needs to be take into account in calculating national biocapacities. For example, if a given country's arable land is three times as productive as world average arable land, then it is necessary to multiply the area of the country's arable land by a ‘yield factor' of three to find the arable area component of the biocapacity.

We may summarise the process of working out biocapacity in this way. We saw that the footprint was worked out in terms of world average productivity and then converted, by equivalence factors , to a standard unit of bioproductivity, the global hectare . Biocapacity is worked out in terms of the capacity of the region or nation concerned. Here one starts with areas in local hectares. These are converted to average worldwide productivities by multiplying by the yield factors , then by multiplying by the equivalence factors , converted to standard units of bioproductivity, global hectares.

So calculating biocapacity involves both yield and equivalence factors, while calculating footprints involves only equivalence factors.

Some workers then make one final adjustment, which is to set aside a portion of the biocapacity for biodiversity, usually 12 per cent. It is then the remaining 88 per cent that is taken to be the ‘available biocapacity' of the region or country.

So, for any country, the total biologically productive land area that would be needed to support the population (the ecological footprint or ‘demand') is compared with the actual biologically productive land (biocapacity) of the nation (with or without deducting 12 per cent for biodiversity).

If the total footprint is larger than the total available biocapacity, there is said to be an ecological deficit or ‘overshoot'. The size of the ecological deficit is a measure of the extent that the region or country is exceeding its share of world resources, or to put it another way, a measure of the extent that it has to rely on land outside its boundaries.

(C) The ecological footprints of nations and the global footprint

In 1997 Wackernagel and colleagues produced Ecological footprints of Nations (7 ) .

This came with spread sheets showing footprint and biocapacity data for countries for which adequate data was available - 52 countries which account for 80% of the world's population (and includes the world's 12 most populous countries). Since then the analyses have been extended to include all countries, as in the WWF's Living Planet Report 2000, which makes use of 1996 data and the revised Living Planet Report 2002, based on 1999 data. In the table below I give data from the latter report for a selection of countries. I have listed the countries in descending population size order, starting with the two most populous countries in the world. Surprisingly to me, as WWF is a conservation organisation, the data presented in the tables of the WWF's reports does not make the adjustment of setting aside a part of total biocapacity for biodiversity, although in the text of the 2000 report, the writers do comment on the overall effect if ten per cent was set aside for biodiversity.

(The published 2002 report - like its predecessor, the 2000 report - gives per capita values to two places of decimals. Now if one wishes to calculate national totals, by multiplying per capita figures by population sizes, which run into millions, a large error could be introduced by using per capita figures that are only at two places of decimals. Now the spread sheet underlying the data table in the 2002 report, kindly supplied to me by the editor, Jonathan Loh, has per capita data to many places of decimals and one can therefore do calculations of national totals with much more accurate per capita figures. Consequently, in calculating national totals I have used the usual spread sheet calculation method which incorporates many places of decimals. In the table below however, I simply record per capita figures to three decimal places)

In this sample, all except Argentina have an ecological deficit or ‘overshoot' as the authors call it (therefore Argentina has a minus sign in the last column – remember the column heading is ‘deficit'). Note that the world as a whole has a large deficit.

Per capita footprint size is correlated with degree of affluence – compare China and India on the one hand, and the USA and UK on the other hand. But what particularly stands out here is that the per capita footprint of the USA is not only far greater than China and India, but nearly twice as big as that of the UK!

Now it is worth noting that of the components of the total footprint (cropland, grazing land, etc), the energy footprint makes up nearly half the total world footprint (the energy footprint is recorded as the CO₂ footprint in the 2000 report, but in the 2002 report the energy footprint is divided between CO₂ from fossil fuels, fuel wood, nuclear and hydro, although the CO₂ is by far the biggest component). However, there is a very unequal global distribution of per capita CO₂ footprints, which is a major cause of the total footprint differences between nations. Here are some per capita CO₂ values from the 2002 report: USA , 5.38; UK , 2.99; Germany , 2.69; Argentina , 0.92; China (mainland), 0.64; India , 0.24; Guinea , 0.05; Mali , 0.02. Note also that the energy footprint is by far the largest component in the affluent developed countries, in poor countries this is not so, in fact it is often not even the biggest component

Large CO₂ footprints relate to the fact that global warming is taking place caused by anthropogenic emissions of CO₂ and other gases. As Rees wrote (3) : “…while the details of the carbon budget may be in dispute, there is no question that carbon dioxide levels are increasing in the atmosphere and that these increases represent about half of current carbon emissions from fossil fuel and biomass combustion. This implies that available land and water carbon sinks are insufficient to sequester all anthropogenic carbon dioxide at current rates of emission. In eco-footprinting terms, our current global energy footprint is excessive. We are running a global carbon sink deficit in exactly the same sense that many countries run a food-land deficit”.

Now the total UK biocapacity is far greater than the total land area of the UK (which is 24,291 thousand hectares). How can that be? The reason is that the biocapacity is calculated using very high UK yield factors – remember that UK agriculture has very high yields through the massive use of insecticides and fertilizers. This serves to emphasise that footprinting analysis as normally practised, has not taken into account the sustainability or otherwise of agricultural practices and energy use; this is only because it is difficult to make the necessary assessments. However, efforts are underway to remedy this: Ferguson (5) reports he has made sustainability adjustments to biocapacity estimates for Australia and the USA . And corrections for sustainability have already been prepared for some fisheries and forests (Jonathan Loh, personal communication).

D) Ecological footprints, carrying capacity and how many people can the world support

What is the relationship between ecological footprints, and carrying capacity, or to put the question differently, what is the relationship between ecological footprints and the maximum population a region/nation/the world can support sustainably?

Well we can begin by asserting that if a country has an ecological deficit, its population is greater than its own land and sea area can support at present levels of affluence and current technology use. It is then a simple matter to find that size of population which corresponds to the country's biocapacity area: we divide the national total biocapacity area by the per capita ecological footprint. For the UK , with the figures given in the table above, this becomes (in millions):

97.615 ÷ 5.345 = 18.26 millions.

So as at 1999, the biocapacity population of the UK was roughly 18 million, compared with the actual population of roughly 59 million, in other words, about a third of the actual population.

Now I mentioned earlier (section C) that the Living Planet Report does not set aside any biocapacity land for biodiversity. If we set aside 12%, which most environmentalists consider the bare minimum, the biocapacity population is decreased from nearly seventeen million to 18.26 × 0.88 = 16.07 million.

Note. This essay should already have made it clear to a reader that the results of footprinting analysis are only estimates, which will have margins of error. But whether or not the biocapacity of the UK was 15, 20, or 25 million hardly matters for the main point I am making here. The UK population at the time corresponding to these footprint studies was vastly in excess of the biocapacity population.

What does the above result mean in terms of carrying capacity? We can say the following:

1) Since the footprinting method is conservative, i.e. tends to underestimate man's impact, and therefore the footprint, we can conclude that the population corresponding to the biocapacity ( henceforth Pb) is probably less than the figure just worked out.

2) Since the footprinting method makes estimates based on current practices, some of which are unsustainable, it follows that a population as big as Pb is not sustainable, without changes in current resource use, affluence and technology.

What we cannot however conclude is that the Pb is not sustainable under any circumstances. For the unsustainability of this population referred to in conclusion number two is dependent on the qualifications stated in that conclusion, namely a population with current resource use, affluence and technology. It is theoretically possible that the country might switch entirely to renewable energy, with such a combination of energy sources that a population as big as Pb could be sustainably supported. It is theoretically possible that the population might radically change its lifestyle so that consumption and production of waste products were massively reduced, this reduction being assisted by radical changes in technology.

However, one may seriously doubt if it would be possible to achieve sustainability for a population as big as Pb, for three reasons. First, a complete change to renewable resources could not be done overnight, it could not even be done in a decade or so. Meanwhile, the damage to the environment continues. Second, we may doubt that people would be willing to drastically reduce their consumption. Third, we may doubt if technological change can be radical enough and quick enough to save the situation.

It is worthwhile in this connection to consider one possible future scenario. Suppose the population of the UK reduced its level of affluence and improved its technology, so that the carbon dioxide energy footprint was reduced to two fifths of its existing value (a massive decrease), and no land was set aside for biodiversity. How would this affect the biocapacity population size?

Using the spread sheets behind the report to enable me to calculate to three places of decimals, the UK per capita CO₂ footprint component of the total per capita footprint was 2.995 global hectares per person ( ghapp ). The reduction would bring this down to 1.198 ghapp . The total per capita footprint was 5.345 ghapp . The revised footprint would then be 5.345 – 2.995 + 1.198 = 3.548 ghapp . Now the population corresponding to biocapacity would be once again national total biocapacity divided by per capita total footprint, i.e. 97.615 ÷ 3.548 = 27.51 million. This is still far, far smaller than the actual population.

Now if we are considering a country like the UK, where Pb is much less than half of the actual population, and if it is doubtful that even a population as big as Pb is sustainable, how much more is it doubtful if a population as big as the actual population could ever be sustainable.

And this brings us to population growth.

We may draw the following conclusions, based on the considerations just presented:

Continued population growth in the UK will only aggravate an already serious condition. The UK population is now about 60 million, but it is projected to increase to nearly 65 million by 2025 – a massive increase. This projected increase is based on past trends. But changes in Government policy could reduce this population growth, and clearly population growth should be avoided as much as possible. Since net immigration is the main cause of future population growth, the UK should, on ecological footprint grounds , prevent any further net immigration.

Now we return to the world scene and the title of our essay.

We have seen that the world has a large ecological deficit. If we perform the calculation I carried out above for the UK , with the whole world, we arrive at a population corresponding to the biocapacity of the earth of 4,984,952 compared with the actual population of 5,744,872 (figures in thousands). And remember that this is leaving no space at all for biodiversity maintenance!

It seems to be the case then, that the world is already grossly overpopulated. Now technology may continue to make big advances, potentially leading to reduced per capita footprints. On the other hand, we need to bear in mind that people in the developing world, in countries like India, aspire to our developed world standard of living, implying increases in their per capita footprints. Clearly we should do all we can to reduce future world population growth and then bring about population reduction.

Finally, I wrote in the first part of this essay:

“Is it possible to determine the earth's carrying capacity? If so, how do we go about it? We believe it is possible through the study of what is called ‘ecological footprints…'”

Now footprint analysis as traditionally practised, does not take sustainability into account – for example, it works out biocapacity in terms of current agricultural practices, which are generally unsustainable. So a biocapacity population size estimate is really only the upper bound for the truly sustainable population size -. the sustainable population size will be smaller. But as I pointed out earlier, current studies are in the process of making corrections which will enable us to determine the size of the sustainable population.

(E) Strengths and limitations of the EF method

Rees (3) argues that the EF approach has conceptual and methodological strengths:

1. The method is highly compatible with other methods for assessing human ecological problems. For example, one method of assessing human impact is the human ‘load' concept as defined by Catton (load is a function of population size and average individual impact). Another is the related I=PAT concept (see our essay on this topic).
2. The EF method, unlike conventional economic models, is consistent with the second law of thermodynamics in that it takes on board the idea that “economic production requires continuous, irreversible energy and material transformations”.
3. The method has a conceptual simplicity and an intuitive appeal. “First, the ‘footprint' metaphor seems particularly effective in communicating the idea that we each have an impact on the Earth for which we are responsible through consumption choices. Second, eco-footprinting consolidates real data on a variety of energy and material flows into a single concrete variable, land area. Land is a particularly powerful indicator because it too is readily understood by ordinary people”

“The method has a conceptual simplicity and an intuitive appeal”. Yes, this is true, but here lies the danger. Van den Bergh and Verbruggen (11) put it this way: “…the EF concept and indicator seems to be accepted almost without any critique by many scientists and policy makers, and especially by environmental organisations”. This may be an exaggeration, but there certainly is some truth in this assertion. Numerous criticisms of the method have been made. The paper just mentioned covers a lot of the ground, and criticisms therein are partly answered by Ferguson (5) .

Some critics have argued that the EF method makes no distinction between sustainable and unsustainable practices. This is correct, although the original practitioners of the method made no claim to be attempting to make this distinction. The method simply reports on mans impact at a given point in time, regardless of the question of sustainability. Consequently the picture of man's impact on the environment that emerges from footprint studies underestimates the likely long term impact of man on the environment. Also, as Ferguson (ibid) points out, the EF method has not taken sustainability into account simply because of the difficulty in making the appropriate assessments; as I noted earlier in section C, he reports he has made sustainability adjustments to biocapacity estimates for Australia and the USA . And corrections for sustainability have already been prepared for some fisheries and forests.

A common criticism is that it is impossible that a single indicator could cover all the complex and dynamic relationships that are involved in modern economies. Rees (3) takes up this criticism. The criticism, he says, misses two points. First, nobody has suggested that eco-footprinting does provide a complete picture of any complex system; it only produces one indicator “…of the state of humanity's ‘engagement' with the rest of nature”. It should be used in conjunction with economic and other indicators that bear on the particular issue being investigated. Second, many phenomena do not have simple explanations. While ‘complex systems theory' might provide insights, “…Occam's razor still applies: there is no need to derive complex explanation where a simple one suffices”.

Some people have argued that the method has little predictive value, and so is of very limited value to policy makers. There may be limitations to predictability, but the EF method was not designed with the purpose of prediction. However, it would be wrong to say the method has no predictive value. While it is true that basically the EF method normally just provides a ‘snapshot' of the present situation, it can also provide a window into the future:

• Once a baseline is established by a study of the present situation, EF assessments can contribute to a time series study – repeated ‘snapshots' over years or decades to monitor change. In a very general way, this can give an eye into the future.

• One can assess the likely impact of specified alternative technologies, changes in affluence, or deterioration of particular area types, in other words, consider alternative scenarios.

Ferng (8) also believes it is possible to develop the EF method so that it can be used in an even more predictive way – to develop scenarios related to specific policy proposals. For this to be accomplished it would be necessary to take into account the various linkages in the whole system of energy pathways (see later). Then he considers it would be possible to introduce economic modelling approaches such as the computable general equilibrium (CGE) model. Ferng goes on to describe a preliminary investigation along these lines based on the situation in Taiwan and a hypothetical scenario where a specific energy product consumption tax is imposed.

As this essay has already made clear, the EF method gives a very incomplete evaluation of mans impact on the environment, which some workers see as a serious shortcoming. As mentioned in the introduction to the essay, it has for example, ignored the effects of toxic chemicals on the environment. Also, a given area of land may perform more than one service, but generally only the chief service provided by the land has been accounted for (avoidance of double counting). While recognising the truth of this assessment of the EF method, we can however reiterate the conclusion that the actual impact of man on the environment is more severe than the impression created by ecofootprinting.

Equivalence factors were initially introduced because sea fisheries have a low productivity compared with land-based systems; they introduce a level of complexity which some think is uncalled for; they would prefer to leave out sea fisheries and equivalence factors from footprint analysis altogether. As David Pimentel wrote, it is hardly necessary to include the sea into ecological footprints “…as the sea provides less than 5 percent of the total food protein consumed by the world's human population and less than 1 percent of the overall caloric intake (Pimentel and Pimentel, 1996). The assumptions needed to establish equivalence factors introduce further uncertainty into ecofootprinting, and they make eco-footprinting opaque for those who have not made a study of the subject” (12) .

The energy footprint is for many countries the largest component of the total footprint. Yet doubts have been expressed about the validity of the carbon dioxide sequestration method of accounting for energy, as discussed in section B of this essay. Furthermore, Ferng (ibid) adds the points that the method used to account for total energy use is oversimplified – it does not take into account all the “linkages among the final consumption of goods and services, final energy consumption, and primary energy requirements”. Such doubts about the largest component of the total footprint at the very least call in question the accuracy of footprint estimates. Not surprisingly it has been suggested that the energy component should be left out of eco-footprint accounts, thus acknowledging that the total ecological footprint will of necessity greatly underestimate mans total impact on the environment, and specifically acknowledging that ecofootprinting would then deal with just a part of the total field of man's impact on the environment.

These and other criticisms should caution us on placing too much reliance on eco-footprint estimates. However criticising the scope and accuracy of ecofootprint analyses is not the same as questioning the basic method employed. And Ferguson

argues that the criticisms do not invalidate the basic logic of eco-footprinting (4, 5).

Numerous workers are currently attempting to improve various components of the analyses; so we may hope that in a comparatively short time (remember eco-footprinting is less than a decade old), we will have reliable assessments of the footprints and biocapacities of nations.

Note. Since this revised essay was put up on the web in early November, I came across a recent assessment of the 2002 Living Planet Report and the eco- footprinting method used therein, by of the Danish National Environmental Assessment Institute (IMV), on the web at www.imv.dk/

This IMV report covers most of the ground dealt with in the   assessment of the footprinting method I gave above. It accuses the Living Planet authors of working from a Malthusian doomsday scenario position – which the IMV authors certainly do not share! They describe the ecological footprinting method and present an assessment of its limitations; they go on to criticise the future scenarios given in the Living Planet Report 2002 (which I did not deal with in the essay).

The IMV report is worth reading, particularly in its study of the energy footprinting methodology. However, I think it is unfortunate that besides presenting their point of view in the three chapters devoted to critical analysis, they allow their point of view to invade the one chapter which should have been neutral – namely the chapter headed “description of the ecological footprint”.

For example, in describing the global cropland area they come out with a quotation from a certain professor Ausubel that if the World farmer achieves the average yield of today's US corn grower, ten billion people will need only half of today's cropland, and at the same time the same farmer will be able to imbibe as many calories as people in the US. My comment on this is US high farm production is only made possible with unsustainable methods that have already led to massive soil loss and water aquifer depletion. If the developing world is to increase its food production to the US level, will it not need to adopt similar unsustainable practices on land areas often already seriously degraded?

An answer to the IMV criticisms is given by the editor of the Living Planet report, available on the web at www.eldis.org/biodiversity/footprintfeature.htm

References

1. Chambers, N. et al. (2000). Sharing nature's interest. Earthscan , London .

2. Wackernagel , M and Rees, W.E. (1996). Our Ecological footprint: Reducing Human Impact on the Earth. New Society Publishers, Canada .

3. Rees, W.E. (2001). Ecological footprint, concept of. In: Encyclopaedia of Biodiversity vol. 2 , Academic Press, San Diego and London .

4. Ferguson , A.R.B. (2002). The assumptions underlying eco-footprinting. Population and Environment 23, 3: 303-313.

5. Ferguson , A.R.B. (1999). The logical foundations of ecological footprints. Environment, Development and Sustainability 1: 149-156.

6. World Wide Fund for Nature (WWF) (2000 and 2002). Living Planet Report 2000 . Living Planet report 2002. WWF, UNEP, WCMC.

7. Wakernagel et al. (1997) Ecological footprints of Nations. Centro de Estudios pare la Sustentabilidad , Mexico .

8. Ferng, J. (2002). Towards a scenario analysis framework for energy footprints. Ecological Economics 40: 53-69.

9. Optimum Population Trust (OPT) (1998). The carrying capacity and ecological footprints of nations. OPT ( UK ), Manchester .

10. Ferguson , A.R.B. (2002). Eco-footprinting's use of ‘worldwide productivity' and ‘global productivity'. Draft article for possible inclusion in the next issue of the Optimum Population Trust (OPT) Journal.

11. van den Berg, J.C.J.M. and Verbruggen, H. (1999). Spatial sustainability, trade and indicators: an evaluation of the ‘ecological footprint'. Ecological Economics 29: 61-72.

12. Pimentel, D. (2002). Contribution to the 2 nd Footprint forum, Part 1. Page 7 of Optimum Population Trust (OPT) Journal October 2002. The reference contained is Pimentel, D. and Pimentel, M. 1996. Food, energy and society. Revised edition. Niwot Co., University Press of Colorado .

Acknowledgements

I would like to thank Andrew Ferguson of the Optimum Population Trust for helpful comments made during the revision of this essay, and Jonathan Loh, consultant to WWF, for providing spread sheets.

(Essay revised Autumn 2002)

© Copyright J.F Barker, 2002

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