In part two, five areas of concern regarding sustainability were covered: the climate system, energy, resources, food and water, and biodiversity. While each area has its own specific issues, this report suggests that there are three general conclusions relating to the overall issue of whether or not we are managing our planet sustainably.

1. There is no evidence that non-renewable mineral resources are in an immediate danger of being completely exhausted. If we consider the situation 50 to 100 years into the future, however, we realize that several high-quality resources may face severe depletion. The real problem may be that there is no generally accepted theory and even less concerted action to ensure the sustainable use of non-renewable resources -whether we talk of the short or long term future.
2. The natural environment is the life support system of human society - the very underpinnings upon which our existence and all our activities depend. Yet this understanding is not shared by everyone, and recent changes in the global environment point to the fact that parts of this support system may be out of balance. Changes in our climate system and widespread deterioration of biodiversity are becoming increasingly apparent.
3. The future of such renewable resources as food, water, forests, and fisheries upon which humanity has relied since long before modern, industrial society is currently in doubt. Mismanagement of many of these resources has endangered the capacity of nature to sustain its productive capacity. In some regions of the world, food and water issues have reached a critical state.

As mentioned above, it is undoubtable that significant and often unpredictable changes are occurring in our climate system, in the biodiversity of ecosystems, and in the area of renewable resources such as food (soil), water, and forests. It is, however, difficult for science to provide exact assessments as to the seriousness of each issue of concern. In such a situation, it is of the utmost importance for us to take the following three actions:

1. Find a sound balance between preventative measures and those based on a cost-benefit analysis;
2. Develop better indicators and monitoring systems to measure the changes in the earth's life-support systems, bringing attention, on both a global and local level, to situations that have previously gone undetected; and
3. Promote understanding of the connections between the ecosystem and human society, and develop new technological and social systems to manage it.

Science is not yet able to prove conclusively whether or not human activity is exceeding the earth's capacity. Aided by simulations and models that often cross the traditional boundary between the social and natural sciences, this issue is the topic of lively debate. How do we achieve a high standard of living for all people on Earth without destroying nature and exceeding the capacity of the earth's ecosystem? That is the topic of the concluding pages of this report.

In 1972, based on the results of a series of computer simulations, a small team of MIT researchers commissioned by the Club of Rome published The Limits to Growth, setting off a great debate that continues even today. A second book was published by the team in 1992 (Beyond the Limits), and a further update in 2004 ("Limits to Growth -The 30-Year Update"). For over thirty years, Limits to Growth has raised key questions about the sustainability of modern society.

The Limits to Growth computer simulation was built specifically to investigate five major trends of global concern: accelerating industrialization, rapid population growth, widespread malnutrition, depletion of non-renewable resources, and a deteriorating environment. The simulation was run multiple times, each time with changes to five key parameters:

• Population (growth rate)
• Per capita food production (kg of grain per year)
• Per capita industrial output (USD per year)
• Relative level of pollution (multiples of 1970 levels)
• Remaining non-renewable resources (proportion of resources remaining in 1900)

The researchers' findings, based on these simulations, were that:

1. If the present growth trends in world population, industrialization, pollution, food production, and resource depletion continue unchanged, the limits to growth on this planet will be reached sometime within the next one-hundred years. The most probable result will be a rather sudden and uncontrollable decline in both population and industrial capacity.
2. It is possible to alter these growth trends and to establish a condition of ecological and economic stability that is sustainable far into the future. The state of global equilibrium could be designed so that the basic material needs of each person on earth are satisfied and each person has an equal opportunity to realize his individual human potential.
3. f the world’s people decide to strive for this second outcome rather than the first, the sooner they begin working to attain it, the greater will be their chances of success.1

The first oil crisis, occurring the year after "Limits to Growth" was published, caused many to view the book as a warning about the depletion of mineral resources. Thirty years later, however, resources have not run out, and known deposits of metals thought to be highly scarce such as lead, zinc and silver have increased, prices have stabilized, and with this criticism has arisen, maintaining that the MIT team underestimated the significance of technological advances and economic incentives.^[4]

The researchers, however, did not actually predict the depletion of any particular resource at a given date. What they did do was to run multiple simulations with varying parameters. Although they did touch on the possibility of "physical resource depletion" for a number of resources if patterns of consumption were not to change, their main findings pointed to the danger of what is referred to as "economic depletion" in chapter three, part two of this report. The researchers' overall conclusion regarding non-renewable resources was that "Given present (1970) resource consumption rates and the projected increase in these rates, the great majority of the currently important non-renewable resources will be extremely costly 100 years from now."^[1]

William D. Nordhaus, from Yale University in the United States, is one among many who have challenged the MIT research team's conclusion that, without a major change in human activity society will hit the limits to growth within 100 years from 1970. In his 1992 paper "Lethal Model 2: The Limits to Growth Revisited,"^[4] Nordhaus claims that "Limits to Growth" has four major weaknesses:

1. Equations and definitions of variables seem to have been invented de novo instead of building on existing scientific knowledge. In Limits I, no attempt was made to estimate the behavioral equations econometrically, although some attempt seems to have been made to calibrate some of the equations, such as the population equation, to available data.

2. The production structure is pessimistic, particularly with respect to the "essential" nature of different inputs. There is no substitution between abundant inputs and limited factors, such as the severely limited natural resource of land. No pollution abatement was allowed in Limits I, although it is possible in Limits II to reallocate capital to pollution abatement activities.

3. Both models rule out ongoing technological change. In this respect, they are inconsistent with the standard interpretation of economic history during the capitalist era.

4. Both models are enormously complex, with a variety of nonlinearities and lags. In light of developments in the understanding of nonlinear systems over the last twenty years, it seems apparent that the dynamic behavior of the enormously complicated Limits I model was not fully understood (or even understandable) by anyone, either authors or critics.^[4]

In an interview for this report, we asked Dennis Meadows what he thought of this upon reflection. This was his reply:

"Our analysis has been misinterpreted. Most people believe our major conclusion was to assert that there are limits to growth. We did say that, but it does not take a computer model to understand that physical growth on a physically finite planet will confront physical limits. Our main contribution was to analyze the dynamics of growth in a finite world (this was the title of our third book in 1974). We said that when physical growth encounters limits the most likely behavior will be overshoot and collapse, not an orderly asymptotic approach to the limits. In our 1972 analysis we discovered in most of our scenarios that the collapse would start around 2030-2050. So it is still too early to tell whether we were right or not. But events over the past 33 years, since our first book came out, certainly tend to confirm our original analysis.”^[6]

With regard to the rise in the price of some metals, Meadows had this to say:

"I have always recognized that physical scarcity an market price are only very loosely related. [...]. I assume that metals prices will go back down as soon as China’s economy cools off, or the producers bring on enough capacity to overshoot demand. With a few possible exceptions, we are not yet witnessing serious scarcity of any metal. [...] And I think energy is now oscillating around a permanently higher average. But I expect metals prices to come back down - at least for some time."^[6]

Is human activity today conducted within the limits of Earth's capacity -or do we already exceed the carrying capacity of the planet as a whole? While a great debate on this issue continues in the scientific community, one particular approach and tool dealing with this issue, "The Ecological Footprint" (EF), has received much attention in both the scientific and political world. While it is not the task of this report to judge whether calculations made with the Ecological Footprint methodology are correct, we still find it useful to describe this tool in some more detail reflecting on the message it brings and its potential value as a guiding tool in economic and resource policy.

Nature provides numerous resources (such as crops, water, lumber, metals, etc.) and ecosystem services (such as the absorption of toxins and waste, stabilization of the atmosphere, and ozone protection from UV radiation) to humanity. Such services provided by nature are called "natural income" (natural flows) while the natural stock which enables the continuous generation of natural income is called "natural capital." Some scientists call for special protection of those types of natural capital that provide essential life preserving services, or "life-supporting natural capital".^[7]

The Ecological Footprint focuses in particular on the global ecosystem's capacity to reproduce natural (biomass) resources and provide waste absorbing functions - based on the maintenance of life-supporting natural capital. It is an index developed to meaningfully compare the supply capacity of nature with the demand from human activity to evaluate whether the two are balanced. Looking at the balance between nature's supply and human demand, the index is used to estimate whether we are in a state of excessive demand (called "overshoot"), and, if we are in overshoot, by how much (Figure 1).

Figure 1: The Concept of Overshoot
Source'Wackernagel, Rees ^[8]

If overshoot caused by economic activity and resource consumption is assumed to occur, this would indicate that, from an ecological point of view, sustainability has not been achieved^[9]. Such information which may help send a signal as to whether our economic activities may be in excess of nature's supply capacity is crucial to the achievement of long-term sustainability. The Ecological Footprint was developed to provide such signals by indicating the balance between earth's capacity and economic demand, an area that is not reflected in current macro-economic indicators such as Gross Domestic Product (GDP), and Gross National Product (GNP), which only measure total annual output in monetary terms.

The scope of the Ecological Footprint is restricted to measuring our economic dependence on life-supporting natural capital biomass resources, or the extent to which economic activity obstructs life-supporting natural capital's production of those resources. As such, metal resources used in factory production are not directly factored in, but refining, treating, manufacture process energy demands, mines, and disposal of slag waste are. The ecological footprint is calculated based on the following six areas, and where there are multiple factors for calculation, the general rule is to choose what will make the footprint smaller (thus making a conservative estimate of the required area).

1. Agricultural land - (land for production of food, feed, tobacco, cotton, etc.)
2. Pasture land - (grazing land, land for production of wool, etc.)
3. Forest - (land for production of raw materials for furniture, building, paper, etc.)
4. Energy land - land for carbon sequestering (forested land needed for absorption of CO2 produced by burning fossil fuels), also "alternative biomass production land" + "water reservoir surface areas" for production of hydroelectric power. In the case of nuclear power, the area of land needed for sequestering CO2 that would have been produced by burning fossil fuel to generate an equivalent amount of electricity is calculated.
5. Land inhibiting productivity - (land being used in such a way that prevents it from being productive. This includes roads, buildings, waste disposal areas, mines for metal resources, etc.)
6. Marine and fresh water - (water areas such as ocean, rivers, and lakes that produce seafood and seaweed)

The WWF International, UNEP, and others have collaborated with scientists to measure the ecological footprint of 150 countries, publishing the results in the "Living Planet Report" in 2000, 2002, and 2004. ^{[10] [11] [12]}

According to the 2004 report, the global ecological footprint reached the earth's limit in the last half of the 1980s, and is continuing to rise each year. In 1987, society's ecological footprint reached 113.3 billion gha (global hectares), surpassing the earth's productive capacity by 3%, and in 2001 total ecological footprint surpassed the earth's productive surface area by 20% as it reached 134.7 billion gha. This means that we would require 1.2 earths to support human economic activity. Figure 2 illustrates how our "ecological debt" continues to grow larger.

Figure 2: Global Ecological Footprint Statistics
Source: WWF Living Planet Report 2004 ^[6]

There are several often-cited criticisms of the ecological footprint method of which five are presented below.

• Criticism 1' The Ecological Footprint calculation is incomplete.
• Criticism 2'Applying the concept of biological carrying capacity to human society is a mistake.
• Criticism 3'When calculating ecological footprint, accounting for changes in land usage makes the assumption that uses are substitutable, but this is not always possible.
• Criticism 4'Talking about carrying capacity is meaningless because the supply of renewable resources can be increased and advances in technology greatly prolong depletion of resources.
• Criticism 5'In a society with free trade, the idea of carrying capacity is meaningless because scarce resources can be imported.

One of the inventors of the ecological footprint, Mathis Wackernagel, as well as Craig Simmons from Best Foot Forward in Oxford, England, and Yoshihiko Wada, from Doshisha University, Japan, have all responded to these criticisms. We shall not cover these responses here, but suffice it to say that it is difficult for science to provide a definitive answer to the question of whether or not humanity has actually exceeded the Earth's carrying capacity. When following the precautionary principle, however, the ecological footprint is a highly useful tool to help identify and manage potential risks relating to sustainability, thus supporting the sound development of society in the 21st century.

Considering the numerous cases throughout history of human cultures being destroyed because they overshot their regional carrying capacity, few would deny that “sustainability” is one of the most critical topics facing society in the early 21st century.

We have mentioned how human activity today may have exceeded the Earth’s global carrying capacity. According to the results of the ecological footprint analysis, human activities (in particular the global economy) are in excess of Earth’s physical capacity by as much as 20%. More important than determining the accuracy of this analysis however, is determining what insights might be gained from such a warning, and where we should focus or efforts to achieve a sustainable economy and society.

If we plot the ecological footprint against per capita GDP, we will find a positive correlation between the two -the higher the GDP, the greater the ecological footprint. If, however, we plot each country’s ecological footprint against the United Nations Development Program’s (UNDP) Human Development Index (HDI), calculated using lifespan, education level, and earnings per-capita, interesting results can be observed (Figure 3).

At one end of the spectrum are countries that can be considered as "unsustainable," with a low ecological footprint and a low HDI. On the other end we find countries with both a large ecological footprint and a high HDI. These too can be considered as "unsustainable" because of their high footprint. In the middle lies a group of countries that may be considered to be the most sustainable (at present), having a relatively small footprint, as well as mid-range HDI values. Most of these countries, however, are moving rapidly toward the upper right, more environmentally "unsustainable" area. Looking at this from a standpoint of “sustainability,” it seems logical that we should aim to develop nations with a high HDI and a low ecological footprint.

Figure 3: Ecological Footprint and Human Development Index
Source: Hong Nguyen, Ryoichi Yamamoto

In the early 21st Century, keeping in mind the basic sustainability principles embedded in The Natural Step’s Four System Conditions and Herman Daly’s Three Principles, all nations of the world face the grand task of designing social and economic strategies that consistently raise HDI while at the same time lowering ecological footprint - something that has not yet happened large scale anywhere in the world. We must continue technological development and promote lifestyle changes to enable this kind of development. Many creative people around the world are working on realizing a “dematerialized service economy”, or on the acceleration of environmental technology development. In addition to such initiatives, we need advancements in environmental technologies, and the internalization of environmental costs through proper measurement tools and the introduction of green taxes and incentives.

This summary report is intended to present a brief bird’s eye view of how science today views the issue of sustainability. Owing to time and budget restrictions, however, it focuses primarily on the natural science aspects, stopping at the bare minimum in terms of the economic or social implications. Examining the importance of infrastructure such as construction, traffic systems, as well as other topics related to the civil and social sciences will be of great importance to act forcefully in our common task to realize a sustainable society for the benefit of all people and peoples on Earth today as well as into the future.
We strongly hope that this body of scientific knowledge (the main report of which is available in Japanese at www.sos2006.jp) regarding sustainability will serve as a foundation for the planning and enactment of concrete policies and strategies.

1. Meadows, Donella. H., Meadows, L.M., Randers, Jorgen. and Behrens III, W.W. The Limits to Growth. (New York: Universe Books, 1972)
2. Meadows, Donella H., Meadows, Dennis L., and Randers, Jorgen. Beyond the Limits: Confronting Global Collapse, Envisioning a Sustainable Future. (Post Mills, Vermont: Chelsea Green, 1992)
3. Meadows, Donella H., Meadows, Dennis L., and Randers, Jorgen, Limits to Growth: The 30-Year Update, (Post Mills, Vermont: Chelsea Green, 2004)
4. Nordhaus, W. D. Lethal Model 2: The Limits to Growth Revisited. Brookings Papers on Economic Activity. 1992, 2:1-43
5. Wackernagel, M. and Rees, W. E., Our Ecological Footprint: Reducing Human Impact on the Earth. (New Society Publishers, 1995)
6. Dennis Meadows .e-mail exchange, 2005.
7. Wackernagel, M., Monfreda, C., Moran, D., Wermer, P., Goldfinger, S., Deumling, D. and Murray, M. National Footprint and Biocapacity Accounts 2005: The Underlying Calculation Method. (Global Footprint Network, 2005)
8. Wackernagel, M. and Rees, W. E., Our Ecological Footprint: Reducing Human Impact on the Earth. (New Society Publishers, 1995)
9. Cotton, W. Carrying Capacity and Limits to Freedom. Paper prepared for Social Ecology Session XI World Congress of Sociology. New Delhi, India, 19 August, 1986
10. WWF, RP, et al. Living Planet Report 2000. (Gland, Switzerland: WWF International., 2000) http://www.panda.org/downloads/general/lpr2000.pdf (accessed November, 2005)
11. WWF, RP, et al Living Planet Report 2002. (Gland, Switzerland: WWF International., 2002) http://www.panda.org/news_facts/publications/general/livingplanet/lpr02.cfm (accessed November, 2005)
12. WWF, Global Footprint Network, et al. Living Planet Report 2004. (Gland, Switzerland: WWF International. 2004)