Sustainable Population Levels

Using Footprint Data

Dell Erickson©
March 20, 2000


The 1995 Study
Table 1. Footprints & Deficits of Developed Nations (1995)
Sustainable vs. Optimal
Findings & Implications
The 1997 Study and Beyond
Table 2. Footprints for 52 Nations and the World (1997)
Growth, Footprint & the Human Condition
The U.S. & the Kyoto Accords
Taxing Emissions
Changing Footprint Scenarios
World Food, Footprints and Population
Table 3. Maximum World Populations
A Moral Dilemma


Wackernagel and Rees determined a single number, the "Footprint" to indicate a nation's impact on the global environment then compares the Footprint to ecologically productive capacity to ascertain sustainability. This paper uses Footprint data to arrive at population levels consistent with the Wackernagel and Rees research. The conclusion is that the world can sustainably support between 1.5 and 2 billion people at the world's average Footprint. It also finds that population's role in determining sustainability is more critical than consumption or Footprint. India, the U.S., Germany, and Brazil are used as comparative examples. The relationships of sustainability to food, energy, pollution, and economics are briefly examined and found to be of minor significance.


Mathis Wackernagel and William Rees in their landmark book, "Our Ecological Footprint", describe human impact on Earth in terms of long term sustainability —the carrying capacity of individual nations and of the world. Their research is based on the concept that for human society to be sustainable it must rely on Earth's natural environmental processes. In human terms, these natural processes are permanent.1

Basing their conclusions on resource use and ecological abundance, other authors (Forrester, Meadows, Pimentel, Ehrlich, et. al.) have quantified possible population scenarios consistent with environmental constraints. Similarly, by integrating population and consumption levels with the available ecologically productive land, Wackernagel and Rees determined what they describe as the "Ecological Footprint" (FP) or impact of nations and of the world.

Wackernagel and Rees contend that ecological resources available for human production and consumption are delimited by natural system processes —air, land and water systems, the resources used, considering wastes produced in the processes and given a human population level and standard of living. An analogy to the "Footprint" is the biological concept of carrying capacity. Due to their temporary nature, the FP analysis does not directly consider additional output due to the use of energy resources such as coal, oil, and natural gas.

Describing the FP in terms of output versus available natural inputs and human impacts, the result is a single number, the "Footprint." The higher the number the greater the human impact with an FP of "0" indicating no impact —an impossibility for a living creature. The range is typically between 1 and 5 with the world average approximately 2.5.

The Footprint is used in two ways:

  1. To compare various nations and project various consumption and population levels, i.e., FP combinations; and
  2. To compare the FP with the nation's or world's ecological capacity in order to determine sustainability.

The Wackernagel and Rees text and associated references should be read for a clearer understanding of the methodology and the sweeping significance of the Footprint work.

Rees describes their approach with the following statement:

A fundamental question for ecological economics is whether remaining stocks of natural capital are adequate to sustain the anticipated load of the human economy into the next century. Since mainstream (neoclassical) models are blind to ecological structure and function, they cannot even properly address this question.2

The economic shortsightedness that Rees speaks to is addressed in this paper in the discussion of GDP and the economy and the efforts to improve the human condition.

When the FP exceeds the region's productive capacity, an ecological deficit is recorded and the area, a nation, or Planet Earth is non-sustainable. Quite literally, the process is, in part, one of exceeding current natural capacities and of mining of capacity produced in previous periods —exploiting the resource base complied over the millennia for the remainder part. An ecological FP deficit reflects an unsustainable situation, thus the degree of deficit implies the relative gravity of the situation. The larger the deficit the more worrisome the situation; indeed, large deficits may imply a resounding sense of urgency to modify existing growth and consumption policies and practices.Note 1

Paul Ehrlich and John Holdren described human impact by the now classic I = PAT formula. Because impact equals population times affluence times technology, I = PAT, consumption, "A x T" is only one of the two primary factors used in determining sustainable populations. The initial Wackernagel and Rees FP study (1995) discounted the role of population while emphasizing the role of consumption in resolving sustainability issues. Subsequent revisions and FP studies (1997, 1999, and expected in 2000) refined the assumptions, methodology, and number of nations evaluated. The studies tended to overstate the ecological foundations of growing populations and understate the resulting consumption patterns. Because the scope of the earlier studies was limited primarily to consumption issues, a welcome change in the later revisions was to acknowledge the population factor impacting the sustainability equation.

In order to answer the question, "What is the sustainable population for a nation (or world) given its Footprint?", the Footprint equation has been rearranged to determine the sustainable population balance level for the world and its nations. The basic procedure was to divide the "ecologically productive land" by the Footprint. For example, Australia's 1995 balanced population of 154,008,824 is found by dividing 575,993,000 by 3.74. Data from other sources —Census, GDP, energy, etc., are then combined in the analysis to determine changes in demography, consumption, pollution, and economic patterns to arrive at sustainable population levels given an FP level.

The analysis involves both individual nations and the world and incorporates historical, current, and projected data. The analysis begins with the 1995 study and then incorporates the 1997 study. Several scenarios are used to facilitate an understanding of the changes in Footprint, population, GDP (Gross Domestic Product), and/or energy use required to achieve population levels in balance with natural processes, the Footprint. A brief diversion is made to discuss items related to the Footprint, GDP, populations, and the Kyoto Accords.

The findings presented in this discussion are based on the Wackernagel and Rees work and should be considered as robust and defensible as that of the original research. The other data sources, e.g., the Census Bureau or the UN, are known to provide reliable data. Consistency of data is important. Due to changes in the manner the data was compiled by the data sources, this analysis used eight years of data in its energy use component. Although the data used was recent and well documented, forecasts of future use patterns based on this somewhat limited sample could give rise to greater variations in possible outcomes than presented here. Nevertheless, the data used is highly reliable and conclusions using that data equally valid.

The 1995 Study

The 1995 study involved the major industrialized nations with the inclusion of India.

The reported ecological Footprints and deficits (if "-") or surpluses are given in Table 1. Column "B," the "Ecological Deficit" is the ecological deficit ("-") found by scientists Mathis Wackernagel and William Rees and given in their text, "Our Ecological Footprint: Reducing Human Impact on the Earth."1 Column "C," the "Balanced Population" is the calculated sustainable population level which is in balance given the nation's standard of living, i.e., Footprint, and the nation's available capacity. It is calculated by dividing the ecologically productive land by the nation's Footprint. The outcome is the maximum population that can be sustained given the nation's capacity resources and its existing standard of living, FP. The "D" column labeled "Departure" is the difference between the actual 1995 population and the calculated sustainably balanced population. The last Column "E," is from the Wackernagel and Rees text showing the percentage change in population necessary in 1995 to reach the maximum sustainable population level, the population in balance with the nation's capacity under average circumstances.

Table 1. Footprints & Deficits of Developed Nations (1995)


Ecological Deficit

Balanced Population


























































So. Korea










United States










Sustainable vs. Optimal

There can be confusion between the terms "sustainable" and "optimal" population. A population "in balance", Column "C", and sustainable under "average" local circumstances is not necessarily the desirable or optimal population level. The sustainable level can be thought of as a starting policy objective rather than long run goal. The FP calculated point of balance should be thought of as the maximum population that can be sustained under average or trendline, conditions. Because a mean "average" year or trendline level is composed of numerous years of sometimes wide variation around the mean average, the actual average condition will occur only occasionally, perhaps 5% of the time.

For example, given short-term changes in something as widely cyclical as weather, implies that a prudent population level will be less than the balanced level. To illustrate, the sustainable target level for the U.S. could be the population given a 100-year drought or flood, i.e., the circumstances during the 1930's "dust bowl" period. A repeat of the weather of the 1930's is simply a matter of time; it's guaranteed to recur —and with the U.S. population now more than twice the size, the aftermath could be difficult to deal with. The loss of small forested areas, shelterbelts and drained wetlands that contributed to the earlier episode, have more than continued. The "old-timers" and their memories have faded; of the 400,000 miles of trees planted subsequently to conserve the soil and water resources, less than 20,000 remain: farmers are planting hedge-row to hedge-row. Tempus fugit.

Because it would require ecological capacity, producing reserve stocks to carry a population through the less productive bad times also implies that the actual sustainable population level be reduced to provide an investment in stored items. The beginning target sustainable population for an area could be twenty million, for example. However, a more prudent actual sustainable population level considering variation around the trendline —with a reliable margin of safety, could be fifteen or ten million or possibly less. Column "C" offers a departure point only.

The larger task is to determine the appropriate lower number.

In addition, capacity used for solar panels, biomass, or other ecologically based energy alternatives further reduces available natural capacity, suitable population level, and biodiversity.

The Footprint deficit and population departure seen in Table 1, column "D", assesses the degree a nation exceeds its ecological capacities, i.e., rising risk, as a nation moves away from its sustainable balance point. It also suggests the scope of policies that may require reviewing. To error on the side of conservatism and safety, that is reduced populations, implies that both human population and other life forms (biodiversity —forests, birds and deer) will have improved conditions under these circumstances. Furthermore, it implies that for many time periods there will be surplus natural capacity, i.e., "good times". Indeed, natural resource related industries such as water and mining, camping and fishing, will find fewer problems to manage. Policies designed to accommodate a rosy-scenario, the highest population potential, suggest the greater risk lies with higher population levels.

Findings & Implications

"Our Ecological Footprint" stresses the importance of dealing with consumption because of its direct relationship to the Footprint calculation and because it is easier to grasp. The 1995 data clearly illustrates (Table 1, Column "B") that consumption is a serious consideration. However, analysis of the data also shows that population is more critical, as the following makes clear.

Because capacities should be considered as fixed in the natural environment , any changes to achieve the balance point involve adjusting the population level, the standard of living, or both.Note 2

Perhaps, the most surprising observation of Table 1 is that all west European nations are impressively in ecological deficit, as are the industrialized Asian nations (- ~700%), with Germany (-780%), England (-760%), and France (-280%) leading the way. The west European nations collectively have a 1995 population departure from a balanced population of approximately 202 million people. This is nearly twice the imbalance of the 1995 U.S. population. Given the large Canadian landmass relative to its 1995 population, it is not surprising to see the additional available capacity. However, as will be seen, its short growing season and extreme cold temperatures suggest that the underlying assumptions should be further tested. Australia is somewhat of a surprise —revised in the next Wackernagel and Rees study to reduce the overstated high capacities for the large Australian deserts.

The U.S. has a large population and high FP but its relatively small percentage deficit (-80%) indicates that the U.S. also has enormous natural productive capacities. On the other hand, of the industrialized nations, the U.S. has the largest population in excess of its balance point, 115.7 million. With its high natural capacity, if a program to modestly reduce its FP were implemented in 1995 and combined with a comprehensive program to stabilize the U.S. population, it would have been a relatively uncomplicated program leading to a sustainable society.

The situation in India is commonly understood. Illustrated in Table 1 Column "D", is India's very considerable population imbalance —departure from sustainable levels of 252 million. India is included because Wackernagel & Rees frequently discuss it as an example of a non-industrialized nation. Even with its humble standard of living (Footprint: 0.38/ha, world average 2.6), its large population remarkably exceeds the nation's modest available capacity. India even with a modest Footprint, has a grimmer population problem than any of the industrialized nations.

Notwithstanding the socioeconomic implications, any attempt to lower its Footprint —further reduce living standards— will do little to ameliorate its dilemmas. Paradoxically, its low Footprint also suggests that it will require liberal reductions in population in order to bring India into balance. Indeed, India has little downside remaining, thus its ability to reach sustainability is little involved with consumption issues; sustainability falls heavily to population management.

It is apparent from Table 1 that even as a nation may attempt to cope with its deteriorating circumstances, a nation can be in chronic, deteriorating, and substantial deficit over a considerable period of time. The reason is due to capacity stored over previous years and imported capacity. Cutting or burning a forest at a rate exceeding its regeneration is an example of consuming stored capacity; food aid is imported capacity.

The population equation is aggravated by what demographers call "population momentum", the momentum of growing populations. For purposes of sustainability, it's the time required to achieve a stable population once a program is implemented. Fifty years is a generally effective planning horizon. Slow growth populations will require longer time periods to reach zero population growth and high growth populations less time. High immigration nations have the ability to quickly reduce or stop population growth by changing policy. Higher growth populations will also have relatively much greater population increases over the time period. The reason is that high growth nations are characterized by having many young in or yet to reach reproductive age.

There is a more inscrutable side to this predicament. Although an abrupt transition away from current population and consumption patterns has been recommended by scientists —including Wackernagel and Rees— the embedded cultures, religions, institutions and politics of each nation suggests that Easter Island may be the pattern followed —the Earth can be thought of as an "island" sphere, where modifying exiting practices may be overly slow to evolve.Note 3

In order to overcome a lack of natural capacity a nation in deficit must import capacity. If there are many nations with excess capacities the situation becomes merely one of allocating and distributing the surplus capacity. When the sum capacities of all the nations are in balance or with a surplus, distributing the capacity involves problems surmountable by traditional economic methods. An economist would maintain, correctly, that international trade and economic policies readily manage this situation.

A more foreboding situation exists if the global ecological capacity and Footprint, exceeds the world's balance point —the Easter Island lesson; at best the situation becomes a zero-sum game. The inhabitants of Easter Island did not have the ability to import additional capacity. The Easter Islanders were fully aware of the limits of their small isolated island, nevertheless were unable to achieve a governing approach or social consensus to establish a sustainable society.

Nations using capacities in excess of their national capacities virtually employ the resources of other nations, perhaps depriving these other nations the possibility of reaching their chosen balance point. That is a purely sovereign national decision. The point should also be made that nations with perhaps heartfelt, perhaps national interests, policies of providing domestic capacities to other nations believe it to be in their best domestic economic interest. From this it follows that neither the deficit nor the apparently surplus nation in this case are practicing long term sustainable social, economic, and environmental policies.

Nations with a higher Footprint should find reducing population growth and levels an incrementally more convincing method of achieving the balance point than reductions in consumption, the Footprint. For example, a nation such as Germany with a Footprint of approximately 4 hectares (ha), implies that each single unit increase in population requires a 4 ha increase in capacity. With its 1995 population of 81.3 million, a 1% population increase would require a 32.5 million hectare increase in capacity. Because Germany already exceeds its sustainable population balance point, the 32.5 million ha additional capacity must come from non-domestic sources. A similar decrease in the German population would proportionately benefit other nations as well by freeing up 32 million hectares for the use of other nations. In relative terms, the same can be said of any nation with a Footprint greater than the world average or in FP deficit.

The 1997 Study and Beyond

The 1995 study was revised and updated in 1997 and 1999. This paper now incorporates the 1997 study revisions, 1999 actual and projected data. The 1997 and later revisions were broadened to include fifty-two nations plus the world and further refined the underlying assumptions. In general, the refinements produced increasingly reliable conclusions. Unfortunately for nations and the Planet, the revised study resulted in outcomes that are less benevolent, the deficits greater, and the maximum population balance points at lower levels than in the previous studies. The 1997 study also demonstrated that few developed or developing nations appear to recognize the impacts of their growth patterns on domestic or global environmental, economic, or social circumstances.3

Table 2. Footprints for 52 Nations and the World (1997)


Ecological Deficit

Balance Population
























2,645, 240






















Costa Rica




Czech Rep
































Hong Kong








































Korea, Rep
















New Zealand
























Poland, Rep








Russian Fed








South Africa
























United Kingdom




United States













Adding significance and enhancing credibility to the 1997 study is the fact that it comprised about 80% of the world's total population, nearly all of those with global environmental impacts, and the fact that these nations constitute more than 94% of the world's total energy use.

The 1997 study with its refined assumptions reinforces the results of the 1995 research: most nations and the world are in deficit —Table 2, Columns "B" and "D". With notable exceptions of Brazil and Indonesia, there are few areas with surplus capacities available for export. It is also apparent from an evaluation of the data that global impacts are incrementally more apparent than related changes in FP or living standards. This disquieting fact is likely explained by population levels.

As Table 2 illustrates, the sustainable population balance of Canada, for example, due in part from further considering cold temperatures, was reduced 63% from 101.0 million in 1995 to 37.5 million in the 1997 study. Because the calculated maximum balance population is approaching the actual current population, those now promoting an increase in the Canadian population will want to reconsider this ill-advised position —Canada will soon join the list of unsustainable nations. Likewise for Australia where its sustainable population balance level was substantially reduced, 81%, —from 154 to 29 million, because its large desert areas on further analysis were found to be significantly less productive than initially thought. And like Canada, Australia is rapidly approaching its maximum sustainable population level and should reconsider its growth policies as well.

India has continued its unfortunate trend in the updated study, adding another 112 million beyond its sustainable level.

On the other hand, primarily because of revisions to capacity for its large coastal regions, the U.S. population balance point was increased from 142.2 million in 1995 to 174.4 million in the 1997 study. The Census data show that 174 million was the U.S. population in 1958, 142 million in 1946. The U.S. fought and decisively won a World War in two major theaters with half its current population, a population level that most would agree, offered a more agreeable place to live. The U.S. would have been not only ecologically sustainable with that population at even today's standard of living and Footprint, but had a safety margin of capacity and readily able to export its surplus to less well endowed nations. Now in a serious and growing deficit, that's no longer the case.

If the world's average FP is considered the goal, the conclusion is that the world could support roughly 3.5 billion inhabitants. Unfortunately, in 1997 the world's actual population exceeded that sustainable number by approximately 2.4 billion. Because the world is gravely in deficit, it implies that the world's capacity utilization is excessive and alarmingly negative. It also implies that it is not a "zero-sum" but a "negative-sum" proposition. Thus, it is the obligation of deficit nations to implement policies designed to achieve target sustainable population levels.

Nations currently in surplus status may want to determine their sustainable population (including a safety margin) in order to assist the deficit nations with their deficits until the surplus nation achieves its population balance level.

Growth, Footprint & the Human Condition

Many western-trained economists and those advocating population growth as a means of improving living standards will want to reexamine their premises. Viewing the world through the mind's eye, one sees that nations with large populations appear to be desperate nations and that nations with approximately equal populations can have widely disparate standards of living and FP. This cursory glance demonstrates that it is likely that factors other than population growth are responsible for improving the human condition.

Nevertheless, these advocates generally support unimpeded population growth because total GDP frequently increases with increasing populations. Using correlation analysis, let's examine the statistical relationships for clues underlying this belief to check its correctness. Correlation examines how closely two or more sets of data are associated. It does not imply that one data set item causes the second item, only that they appear to be related. The higher the correlation, the greater the apparent relationship.Note 4

Supporting the view that more population is good, the 1995 study has a solid correlation of 0.96 between total GDP and total population.4 The use of energy is a sound measure of the standard of living, thus, it is consistent to note that per capita energy use correlates 0.85 with national Footprints.5 However, the correlation of per capita energy use to national GDP falls to a statistically unrelated 0.34. On the other hand, as this statistical group is skewed toward developed nations and their generally low populations relative to GDP, the correlation of total GDP to per capita GDP is only 0.41, i.e., not correlated. Reinforcing the 1995 study (and pro-population growth supporters) the 1997 study improved the correlation between total GDP and total population to an impressive 0.99. However, in industrialized countries the critically important per capita basis, the relationship with a correlation of 0.06, does not help explain the increase in GDP. In other words, the data support the idea that the greater the population, the larger the total GDP, but not necessarily energy use, standard of living, or emissions.6

The conclusion is that what may appear reasonable in macroeconomic theory fails when considering the individual effects. In today's economic and natural environments, the data suggests that contrary to the promise of economists, increasing populations actually decrease the national per capita standard of living. Using the nations in the Wackernagel and Rees study illustrates that population growth does not contribute to increases in individual well-being, per capita GDP. Similar to the correlation of total GDP and population, this relationship is also supported by the finding that in the 1997 study total energy use is essentially unrelated with a correlation of 0.70 with per capita GDP and at the per capita level, the 0.34 correlation indicates other factors explain economic success and the FP.

Of interest is the virtually absent and somewhat negative correlation of energy use to population, -0.27, as well as the correlation between national population and the national Footprint at -0.29. In other words, increasing population negatively impacts energy and living standards.

Finally, because of their dominating influence, when the U.S. and Canada are statistically removed from the 1997 study sample, the relationship of per capita and total GDP growth becomes even less connected —if not disconnected. It is clear that in developed nations factors other than population explain increases in GDP, while in developing nations population increase in great measure explain increases in total GDP.

This finding is consistent with the economic concept of "returns to scale". Once the point of diminishing returns is reached, although absolute quantities increase, incremental marginal returns begin to reverse and decline; a point is reached where further production produces increasing losses and diminishing sustainability. The distribution of the world's natural energy and water resources also serves to restrict local economic developments. The data suggests that global impacts rise with increasing energy use and national Footprint. Thus, economics working through the immutable laws of physics explains why superficially population growth appears economically beneficial. The growth concept is built on feeble foundations, foundations that literally begin to implode at some point. The complete breakdown in the apparent association between total and per capita GDP, energy use, and FP as populations enlarge fails to support the pro-growth position.

This is a powerful argument supporting programs designed to achieve sustainable population levels based on Wackernagel and Rees's determined carrying capacity. These findings support the argument that dealing with consumption is not a necessary consideration for developing nations, nor a sufficient consideration for developed nations.

The U.S. & the Kyoto Accords

Although the purpose of this paper is not to criticize the Kyoto Accords, it needs stating that the Kyoto Accords appear to emphasize political viewpoints over science; the science is in energy and emissions related to FP. Energy production is the primary contributor to greenhouse gases. If, as the Accords presume, greenhouse emissions are an important cause of climate change, then the critical factor is the total quantity of emissions not the source nation. Because the Accords do not identify acceptable total global emissions, there is no scientific goal to pursue. On the contrary, the Accords permit non-U.S. nations to increase greenhouse emissions and FP without limit. By focusing on unlimited global and restricted U.S. emissions, it is clear a political rather than scientific agenda is at work.

With a moderately vague correlation of 0.86 of energy use to a nation's Footprint and a weak 0.70 correlation of energy use to GDP, but a robust correlation of 0.97 of total U.S. greenhouse emissions to U.S. per capita population, it may be an informative diversion to very briefly mention the associated emission, GDP, and population changes required in order for the U.S. to meet the Kyoto Accords. Thus, the following discussion combines the Footprint approach with greenhouse emissions to demonstrate the economic impact that would be required by the Accords.

The Accords require that in the year 2010, U.S. greenhouse emissions be no greater than the levels of 1990.

The proposed changes in emissions would have considerable economic impacts. With a near perfect correlation (using the most recent, 1998, data) of almost 0.99 between total GDP and total emissions, any change in emissions will seriously impact the American standard of living as measured by GDP. If the annual 0.75% average increase in per capita emissions over the period 1990 - 1997 is used to grow emissions to that of the Accord target year, the result is a reduction in total U.S. emissions of 18.5%. Because of the near perfect association of total GDP and total emissions, it is reasonable to assume a similar reduction in GDP would follow.

The U.S. is the world's largest exporter and exports make up a significant percentage of GDP and contributions to its FP. Statistically, the high correlations suggest an 18.5 or 30 percent reduction in emissions will create a proportional decrease in U.S. GDP. Therefore, if Americans chose to, a substantial portion of the required FP decline could come from export reductions. As indicated above, a 30% reduction in FP could imply a similar reduction in exports and would take the U.S. Footprint below that of Canada and slightly above the European levels. The effects on employment, for example, would be staggering and unprecedented, profoundly affecting the social and economic fabric of the country. The resulting environmental backlash might encourage the return of U.S. environmental standards to a less regulated earlier period.

The reductions would also result in similar effects on the importing nation. For example, if the importing nation chose to manufacture the goods formerly imported (rather than do without), the goods would likely cost more (reducing domestic employment) and merely shift the FP circumstances from the U.S. to the other nation. In other words, shifting energy use and emissions to other countries will not reduce greenhouse gases. This less regulated period it should be noted, is the model now prescribed by the Kyoto Accords for other nations.

The UN estimates that 95% of the population growth coming in the developed world will occur in the U.S. Please note that this is a statement of a UN projection not destiny, only policy. Yet, as the data clearly illustrate, U.S. population growth from any source exacerbates the FP and emissions situation and promotes domestic and international social instabilities.

Growing the U.S. population to that of the Accord target (300 million per the Census, 306 million using linear regression, 310 million for Census high projection) produces a significantly larger reduction of 28.4% rather than 18.5% using Census mid level data, almost 30% using regression techniques, and a 31% reduction using the Census high growth projection. The Census high projection has been the U.S. population growth trendline of for about three decades. With a 0.97 per capita correlation, one may argue that an unintended outcome of Kyoto is to substantially reduce —by approximately 31%— the U.S. standard of living or Footprint in order to meet the Accord's U.S. emission standards.

In contrast to the U.S. standards, the other significant greenhouse gas emitters (excluding China and India who are not required to control emissions), Japan and much of Europe and Scandinavia have stable or slightly declining populations. Thus, for most other contributors to greenhouse emissions to meet the Accords (not a requirement) is essentially a non-issue, simply maintain the status quo, maybe add a scrubber or two or slightly increase efficiency.

Increases in efficiency, however, only accommodate increases in population with little, if any decrease in emissions. (Germany and Canada due to immigration mirrors the U.S. dilemma for meeting any of the Accords.) As discussed earlier, a growing population is expensive, mandating continual increases in technological efficiency and retrofitting costs only to maintain current levels and FP. The increased effort and expense do not yield decreasing emissions. It's an epic struggle in the Sisyphusian sense: growth without increasing emissions is a heavy rock; the hill, steep; the outcome, known.

The Accord's U.S. emissions requirement also implies that emissions control technologies will be discovered or are prohibitively expensive will be installed. Ironically, because the U.S. today has superior efficiencies and the most effective worldwide environmental regulations, the incremental cost of cleaning that last few percent of emissions becomes prohibitively expensive. The underlying reason is the Law of Diminishing Returns. Cleaning the first 90% is relatively inexpensive; the next 5% comes at increasing per unit cost. The final few percent may be more expensive than all the costs of greenhouse gas removal that went before. Thus, the U.S. GDP will decline and the FP effects transferred to other nations with increased or no reduction in global greenhouse gases.

As of this writing there has been no statistically significant reduction in U.S. greenhouse emissions, therefore any forthcoming reductions to meet the Kyoto accords will require a technological and logistical tour de force never contemplated or agreed to by Americans nor, possibly, considered by the Accords.

Taxing Emissions

From an ecological/economic perspective, a more effective and lasting approach would be to tax emissions equally in every country and to have the tax ratchet higher with higher levels of per capita emissions. This method has the feature of tracking Footprints. Adhering to the Precautionary Principle, the tax should be set to achieve the global greenhouse gases target level —at the level where natural environmental processes could safely manage the remaining emissions. If human society doesn't suffocate her, Gaia can do the job! Only in this manner will the cost of emissions be incorporated into production costs, consumption, and resulting Footprint.

It would also discourage the current practice of subsidizing unrealistic consumption while encouraging pollution. Furthermore, because it would be central to the pricing system, a nation or economy will adapt to the price structure and produce the emissions reduction transition over a shorter period of time. Unfortunately, because these subsidizes have numerous allies justifying the Kyoto Accords (UN nations), they are quick to come to its defense.

Changing Footprint Scenarios

In 1995 the industrialized nations average Footprint of 2.6 is close to the 2.8 average of the larger 1997 study. Nevertheless, in 1995 the developed nations already had reached a level 58%, or 263 million inhabitants beyond the maximum sustainable population balance point.

An appropriate question to ask is, "What are the Footprint and population levels the world and individual nations should attain in order to employ a sustainable nation or world strategy?" Let's examine some samples, beginning with India, then Europe, the U.S., and conclude with the world.

Wackernagel and Rees discuss India at some length, therefore India will be used as an example of how low Footprint nations can be in serious sustainability situations —certainly at least on parity with the relatively high Footprint areas. Those that hold the romantic view that returning society to standards of living characterized by the "Little House on the Prairie" or Medieval periods will want to reconsider. Those who hold the belief that India has the wherewithal under current policies to achieve a satisfactory population level have yet to examine the numbers. If nothing else, India is a vivid and frightening example of the consequences of population policy reversals agreed to at Cairo 1994 and Cairo +5 conference this year. Asserting that happy "empowered" women will forthwith resolve population induced energy, economic, and environmental problems, these conferences rejected the foundations of numerous previous conferences —rejected all issues involving sustainability and of numbers.

As mentioned earlier, with a 1995 population of 910 million and a Footprint of 0.38, its current population imbalance exceeds 252 million or 58%. In 1997, its deficit expanded to 60% or 363 million people. Using the actual 1999 population of 1,007 million and assuming a small increase in the living standard to a Footprint of 0.5 results in a deficit of 50% or 507 million people too many.

More than doubling the Indian standard of living to a Footprint to 1.0 produces a 75% ecological capacity deficit, equal to an overage of 757 million people (still at less that half the world average FP). Looking out to the year 2050 with India's projected population of 1.7 billion and assuming a 0.5 Footprint produces a 71% deficit or a staggering 1.2 billion people too many. In other words, with only a slight improvement in living standards, in less than 50 years, India will have a population imbalance equal to China's total population today. Note that the UN population projections do not assume insignificant fertility declines. If, in a misguided effort, the people of India decided to plan to accommodate an increase in their population by choosing to further reduce their standard of living and FP from the already low 1995 FP of 0.38 to the barely substance level of 0.25 at 2050, the nation would nevertheless remain in an unsustainable 41% deficit with an imbalance of over 707 million people. That's 707 million people beyond a sustainable level even at a bare subsistence living standard. A single year with a routine minor drought or crop lost to disease will produce an unimaginable national calamity.

The predicament of India can also be examined from the perspective of the additional ecological capacity required to provision the population overage (measured in hectares/acres of land). Using the FP and population information in the preceding two paragraphs, with an imbalance of 507 million people an additional 253 million hectares (625mm acres) are required (FP = 0.5) to produce for the increase; with 707 million (FP = 0.25), 176 million ha (435mm ac.); with 757 million (FP = 1.0), 757 million ha (1,870mm ac.); with 1,207 million (FP = 0.5), 603 million ha (1,490mm ac.).

Planet Earth is not expanding and new land not being created. Where will the land and additional capacity come from?

Because there is no available global surplus capacity, the growing Indian capacity deficits also indicates the quantity of capacity that must be mined from prior accumulations or imported each year, purchased (or given as aid) from other areas. If one assumes the 1995 world average Footprint of 2.6, India's deficit (assume 500 million ha, 1,235mm acre deficit) implies that other nations must either forgo 192 million people or substantially reduce domestic consumption of natural capacity in order to support the additional Indian population. If capacity is not imported, then the capacity in inventory will one day be exhausted.

The UN needs to reconsider its position regarding its population policies toward Western Europe (and the U.S.). Apart from the issue of sovereignty, the UN notion of resolving alleged Western European pension problems through large scale population growth from immigration is more than culturally and economically in dispute. Increasing their populations from large-scale immigration will significantly impair European efforts to achieve sustainable societies. In discussing the 1995 study, the German population - FP connection was discussed in terms of the effects on the world's capacities. The Wackernagel and Rees research found, for example, that Germany, like India, is in serious deficit at this time (-780% in 1995 and -179% in the 1997 study) and requires importing substantial capacities in order to maintain its current population.

Although the UN has not addressed the issue, if Germany is to conduct the UN's immigration policy, the importation of additional capacities will be required to match any increase in its population. Because of its relatively high standard of living and FP, any population increase can be supported only by significantly decreasing the potential standard of sustainable living and population levels of the source country of the capacity. Germany mirrors India in this regard. When Germans already need to reconsider population growth policies, serious public discussions regarding reductions in standard of living and FP solely to accommodate increases in people from foreign lands would be expected.

The identical situation prevails regarding the U.S., only the affects are proportionately greater —and worrisome. According to Wackernagel and Rees, the U.S. has far greater natural ecological capacity than any other nation and can therefore, sustain a larger maximum population than any other nation. As stated earlier and noted in Table 2, even at its relatively high current standard of living the U.S. could sustain a population of 174 million without impacting the global capacity or FP.

Using the most recent population data (1999) for the U.S., 275 million and assuming a dauntless 50% reduction in the 1995 standard of living or FP from 5.1 to 2.55, a maximum sustainable U.S. population balance point is slightly above the current population of 284 million. Thus, it may surprise some to learn that even if the U.S. lived at the world's average standard of living, an FP of 2.6, this much maligned nation is in the same boat as other nations,  —could sustain no more than its present population from domestic capacities.

The research demonstrates that any increase in the U.S. population above 174 (or even 275) million at the world's average FP, requires non-domestic capacities or substantial and continuous reductions in standard of living. In other words, any increase in the current U.S. population even assuming half the current standard of living, is further destabilizing and negatively impacts the global environment. Clearly, those compassionate worldly individuals advocating that the U.S. be a relief valve for the population dilemmas in other nations seriously need to reconsider this heartfelt position. Moreover, steadily impoverishing Americans, particularly the American poor and disadvantaged by immigration-driven population growth, will likely turn Americans inward and compel the otherwise generous American to reduce economic and other foreign aid.

Developing a prudent U.S. population policy that endeavors to achieve a sustainable U.S. population level as soon as practicable would appear in the world's best interest.

World Food, Footprints and Population

The role population plays in determining sustainability levels is shown by examining the quantity of capacity available per person by country and for the world.

Although firmly in the unsustainable camp, the U.S. is a substantial exporter of food —exporting domestic capacity. However, the expected "surplus capacity" (food production) is heavily dependent on the "Green Revolution" and it requirements for substantial energy in the form of oil and natural gas and dependent on substantial volumes of water. With apologies to the original author, "agriculture is a means of converting oil and natural gas into food." However, the timeline of these resources is rapidly drawing to a close. When these commodities become increasingly scarce —sometime in the present decade, the Green Revolution's dream will fade —food and its export will decline in tandem.

The bottom line is that U.S. agriculture will soon begin —if it hasn't already, a return to an earlier agriculture stage using seed (hopefully saved, archived older versions?) that are adapted to local environments requiring less artificial energy and water for crop production. Thus, India and other deficient nations now dependent on exported American capacity —temporarily increased by technology and energy— will find it increasingly necessary to rely on domestic ecological capacities. In this regard India is merely one example of many profoundly deficient nations.

The capacity requirements and world population land impacts can be calculated. According to Dr. David Pimentel, every additional American requires approximately five hectares of non-domestic, global capacity and that that requires at least the capacity of ten non-Americans, and perhaps as many as thirty, to provide for each additional U.S. inhabitant.7 The capacity consequence is that for each additional person of annual U.S. population increase of approximately 2.6 million (or Canadians or Australians, etc.,) will have the same capacity impact as between 25 and 65 million other world inhabitants. It also implies that even at the world's average FP, because an American average equal to the world —a 1 : 1 relationship, implies that every increase in U.S. population implies a corresponding increase in ecological capacity needed to support that person. To be sustainable, additional capacity must come from foreign sources. This would be the inevitable result unless the intention of world policy is to drive the U.S. FP below the world average —in the end, below that of India's.

Wackernagel and Rees calculate that there are 7.4 billion hectares (3 billion acres) of capacity available for humans in the world. With a world population of six billion at the beginning of 2000, the implication is that today, on average, there is an inadequate and grimly unsustainable 1.23ha (or 1/2 an acre) available per person. If the world had two billion human inhabitants the result would be a sustainable 3.7ha (1.5 acres) per person. Dr. Pimentel concludes that 1.5 acres is the minimum amount of land to sustainably provide for one person.

The world average can be separated into the industrialized countries with an average of 2.52ha (1 acre) and the non-industrialized nations with an average 1.05ha (0.4 acre) per person. Countries with modest populations relative to their total capacities such as Australia, Canada and the U.S., although in deficit, contribute to the higher industrialized country average. On the other hand, those nations such as India, China, Bangladesh, and Indonesia with large populations relative to their capacity reduce the non-industrialized average capacity.

Note that the important relationship is between population and a nation's available capacity not its Footprint. Two nations with the same available ecological capacity can choose to support very different standards of living (Footprint) depending exclusively on their chosen population level. Indeed, one nation can be in balance while the second nation perilously unsustainable. Although an imperfect analogy, the nations of China and Brazil have similar total capacities, however, China is confronting an indeterminate future while Brazil, according to Wackernagel and Rees, has available capacity to more than double its current population at its current Footprint.

As Brazil improves its standard of living and FP, however, its sustainable population level will markedly decline. Because of population momentum, the FP and ecological capacity constraint also suggest that Brazil implement a population policy at this time to avoid exceeding its maximum balance population level. With a forward thinking policy rather than using available capacity to provision an increasing population, a portion of its surplus capacity could also be exported to capacity deficient nations. Brazil is also reducing its available capacity by rapidly burning its forests and turning the areas into desert-like regions in this otherwise rainforest. Note that Brazil already has serious environmental problems. For example, air pollution in San Paulo, its largest city, is already creating serious health concerns.

A similar analysis can be performed for any of the nations and for the world. The 1997 revision included a much larger and divergent set of nations than the 1995 study and the year 2000 update will include even additional countries and Footprint data. However, as briefly described in this essay small incremental improvements in methodology may refine the data but not its significance nor suggest unconventional solutions. The world and its many separate nations are progressively moving further away from sustainable maximum and optimum population levels.

Combining various Footprint levels with the world's current population of six billion produces the following maximum sustainable world population levels.

                                      Table 3. Maximum World Populations 


Bal Population

FP Reference


18.40 b



9.25 b



4.11 b

South Korea


2.96 b

Slightly below European


1.85 b

Slightly below Canada


1.48 b

United States

        b: billion

The UN currently projects the world's population at 2050 to be between nine and ten billion. In order for that population to be sustainable, Table 3 indicates that the highest sustainable average living standard would be approximately 0.8, about the living standard and FP of Ethiopia today. This is a difficult and harsh standard of living that all nations have struggled for centuries to move away from —approximately one-third the current world average standard of living. The scientists mentioned in the opening second paragraph concluded that approximately 2 billion inhabitants is the maximum sustainable population level. Table 3 illustrates the approximate living standard that the population level could support under average circumstances as determined by Wackernagel and Rees. Thus, the 2 billion maximum stated by other scientists is consistent with the work of Wackernagel and Rees.

Providing for a degree of volatility around the average implies a reduced population level or targeting a living standard significantly below the current world average. A margin of safety implies that the world's prudent carrying capacity using Wackernagel and Rees's research is on the order of 1.5 billion or fewer inhabitants.

A Moral Dilemma

Where does the responsibility for action rest —nationally or internationally, and to what extent are assistance programs appropriate?

In a real sense, all nations or regions start equally —with the same opportunities. How the opportunities are pursued —the FP and living standard seen today— is arrived at from choices and decisions made by local inhabitants. The unequal distribution of natural capacity and other resources is not a relevant factor; resource levels only impact, even then indirectly, the sustainable population level not the Footprint and living standard.

Garrett Hardin's "lifeboat ethics" essay addresses this question.8 Those who argue that it is a global concern appear to avoid the issue of national sovereignty and responsibility in terms of both cause and remedies. Overlooked is the unforgiving fact that, regardless of an individual nation's Footprint, in a world where nearly all nations exceed their maximum sustainable population level, at best, a zero-sum situation exists. Providing capacity to other nations implies reducing one's own nation's sustainable population level and Footprint  —and continual declines in standard of living. In a literal sense —especially considering immigration— it also intimates that individuals in exporting nations are being replaced by those in capacity importing nations —those inhabitants in or from the other less well-situated and frequently unaccountable countries.

If Hardin's "lifeboat" ethics and it displacement connotations is misplaced, then capacity-importing nations must be able to continue current practices without limit.


  1. The balancing sections are calculated using Footprint, United Nations, and U.S. Census Bureau data.
  2. Essentially, changes would imply modifying an ecosystem. Even on the level of the farm, for example, the addition of fertilizer may increase the per acre yield, but the economics and environmental consequences are frequently negative because the increased energy and wide ranging environmental costs greatly exceed the increased energy output in the form of food, therefore, self-limiting and temporary.
  3. Easter Island is well known for its more than 600 very large stone statues (Moai). Many wonder how such large statues came to be and how they could have been erected. Many others are coming to understand it as a possible metaphor for nations or the Planet today. The Easter Islanders although fully aware of the closed nature of the Island system, were unable to deal with it. Originally it was a completely a forested island, later, fully cleared. The example of Easter Island suggests that politics and Human nature may be our most intractable adversaries. There are numerous other historical examples of humans acting less as sentient beings than simply another boom and bust life form. The Easter Island "homepage" is found at < > and its ecological situation discussed at < >. Easter Island's civilization lasted about 50 generations, roughly 1300 years. See, Sundquist, Bruce. 2000. "Some Lifetimes of Civilizations", at < >, (about 1/4th down).
  4. Statistical correlation attempts to describe the strength of a relationship between two (or more) series of data. The result is a single number between +1 and -1 with strength indicated by numbers approaching +-1. The sign, + or -, are equally significant, the "-" sign indicating that one series increases as the other decreases, negative correlation. As the number approaches zero a decreasing statistical relationship is apparent. It must be said that causation is not a condition of correlation; although an intuitive connection helps provide understanding, technically, the data sets can lack even a common sense link. Rain in the northern hemisphere, for example, is often preceded by wind from the east, yet easterly winds do not cause rain.


1. Wackernagel, Mathis and Rees, William, 1996. Our Ecological Footprint: Reducing Human Impact on the Earth. New Society Publishers, P.O. Box 189, Gabriola Island, B.C., Canada VOR 1X0. Note pages 85, 88, and 97.
2. Rees, William E., "Revisiting Carrying Capacity: Area Based Indicators of Sustainability." Population and Environment: Volume 17, Number 3, Human Sciences Press, Inc. January 1996.
3. "The Ecological Footprint of Nations"; updated Dec. 1997. "Nations Rankings", See at < >. Revised using "equivalency factors, new forest productivity, CO2 absorption, and ocean factors."
4. Derived from data from, "Total Output, Income, and Spending: Gross Domestic Product," Department of Commerce, Bureau of Economic Analysis. U.S. GPO. March 13, 2000. See at < bin/getdoc.cgi?dbname=economic_indicators&docid=01fe00.txt >.
5. Derived from data from, "Energy Consumption and Production by Country, 1990 & 1997". U.S. Energy Information Adm. In, The World Almanac 2000. p854.
6. 1995 data. United Nations Statistical Yearbook, 42nd Issue, 1997. "Current prices," p159.
7. Pimentel, David. "U.S. Food Production Threatened By Rapid Population Growth," Carrying Capacity Network, 2000 P Street, NW; Suite 240, Washington, D.C. 20036.
8. Hardin, Garrett, 1974. "Living on a Lifeboat." Originally published in BioScience, 24(10):561-568. Also see Chapter 30, "Living on a Lifeboat", and Chapter 31, "Trouble in the Lifeboat", 1978. In, "Stalking the Wild Taboo", 3rd Ed. 1996; The Social Contract Press, Petoskey, MI.

[MFS note: works of several of the cited authors are available on the "Sustainability Authors" page here. Also, there are several items mentioning Footprint works and Easter Island on this Website ─please use the "Search" feature.]

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