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Population as a Sustainable Scale Problem
Overpopulation Means Over Consumption
“Overpopulation” occurs when a population’s consumption exceeds the capacity of its environment to support it. The current global population is consuming some 20% more than the annual bioproductive capacity of the earth ( ). This is not sustainable. Just a few  specific examples of consumption exceeding replacement include:

Exponential Growth Unsustainable 
Between 1650 and 1965, the human population displayed super-exponential growth. While this rate has slowed significantly since 1965, the 77 million people now being added annually generate additional throughput which contributes to further ecosystem degradation. At the current growth rate of only 1.2% per year the human population will double in only 58 years. Exponential growth of any living system is a physical impossibility (Bartlett, Meadows, Cohen ,site ).  Such growth cannot continue: the question is whether the transition to a sustainable population level will be chaotic or planned.

Stable Population Not Necessarily Sustainable Population
UN projections that the human population is likely to stabilize sometime in the current century are taken as a positive outcome by some analysts (ref?).  A stable population is certainly better than a population continually increasing, even if at a very low rate. However, a stable population, especially one at the expected level of 9 billion, is not sustainable if its consumption exceeds what the earth can produce annually.

Given that the world’s bioproductive capacity has an upper limit, more people can only mean a lower level of per capita consumption.  Current attempts at dealing with the population problem are attempting to increase per capita consumption as a means of decreasing fertility.  If global per capita consumption occurs along with a 50% increase in population, total consumption will even more seriously stress global ecosystems, making it increasingly unlikely that sustainable scale could ever be achieved.

Population as a Major Driver of Consumption (Throughput) 
The IPAT equation (The IPAT Equation ) reminds us that environmental impact is a function of consumption, technology and total population. Our current levels of consumption are already in an “overshoot” or unsustainable level (see Ecological Footprint, and Areas of Concern).  Adding an additional 2 to 5 billion people by 2050, at the current level of per capita consumption, will only exacerbate the problem of ecosystem degradation.  Each additional person requires additional food, shelter, education, medical care, energy and a variety of basic material amenities for a dignified existence.

While it is difficult to predict further population levels with much precision, it is clear that the human population will continue to grow for at least a few decades. Without radical decreases in per capita consumption, and/or radical increases in technological efficiency, whatever population increases occur will increase the currently unsustainable level of material throughput. Public policies which target even lower fertility rates would facilitate the transition to a level of sustainable throughput necessary for a healthy population on a healthy planet.

Estimating Carrying Capacity for the Human Population
Various attempts have been made to determine the highest human population that could be supported by the earth’s resources (cohen p 40?).  Some of these estimates are little more than ideological statements; some reflect attempts to consider various limiting factors such as food or water availability.  Estimates range from 500,000 to tens of billions.  Most of these estimates are generated to demonstrate that there are one or more limiting factors, and to estimate what the population might be if brought up to these specific limits. 

Very few attempts have been made to actually consider the earth’s human carrying capacity at various consumptions levels, and the impact of technology on population levels. [do we have any examples??] What is clear is that current population levels are not sustainable with present technologies and consumption levels in developed nations. If the earth’s population of 6.3 billion people were to live at the consumption levels of North America, three or four additional planet earth’s would be required to provide the material throughput ( ).  Clearly, the planet cannot provide material throughput for the additional 2 to 5 billion people expected by 2050 at this level of consumption.

What Level of Consumption is Sustainable?
Total consumption levels, regardless of population and technologies used, must not exceed the biophysical limits of ecosystem renewal; this is the definition of sustainability.  What is clear is that the choice we must make involves aiming for higher levels of per capita consumption with a lower population, or a lower level of per capita consumption at higher population. What is fixed is the total level of consumption possible if sustainable scale is to be achieved.

Currently, total global consumption levels are determined largely by market factors. Biophysical limits of ecosystem are not considered in determining global consumption, although they, and not market issues, will ultimately set the limits.  Accepting these biophysical limits as key determining factors from a sustainable scale perspective forces us to consider what levels of per capita consumption are acceptable given the population and technologies we now have.

What Level of Consumption Do Humans Need?
Consumptions levels vary greatly between nations. Using the Ecological Footprint as the indicator, the United States now uses 9.57 global hectares per capita to support its consumption habits. China and India use considerably less on a per capita basis (1.36 and 0.76 global hectares per capita, respectively).  However, the Asia-Pacific region as a whole has by far the greatest aggregate level of consumption due to its large total population.

It has been argued that consumption patterns in developed nations are wasteful, whereas those in the poorest countries barely allow a subsistence existence. Mortality and morbidity is many times greater in the poorest countries, and more than two billion people survive on less than $2 a day.  Very few nations consume at a level close to the “equal earth share” of approximately 1.8 ha per capita (the total amount of bioproductive land and sea areas available divided by the global population). Nations whose ecological footprint are close to this “equal earth share” (e.g. Albania, China, Uganda, Tunisia, Botswana, Honduras, Indonesia, etc) are generally aspiring to achieve higher levels of consumption, as are all other nations.     [need to ensure all these figures are up to date]

Clearly, this “equal earth share” would be higher if global population were smaller.  It may be argued that a desirable and sustainable level of per capita consumption is somewhere between the excesses of high footprint countries (e.g United Emirates, United States, Kuwait) and the poverty of countries at the low end of the footprint spectrum (e.g. Afghanistan, Somalia, Haiti). This approach is based on the understanding that a certain level of material consumption is essential for human well being and happiness (Understanding Human Happiness and Well Being), but that non-material issues are also highly relevant to these issues.  Exactly what level of consumption is desirable and sustainable has yet to be determined (see below Additional Solutions for Population ).

The Role of Technology
Technology is a key factor in determining total consumption or throughput.  The cheap energy which characterized the past 150 years is now peaking and less energy is likely to be available in the next few decades (see ).  The great increases in productivity and technological innovation have relied heavily on this cheap energy.  Sustainable technologies are being explored (see Sustainable Business Practices) to both increase efficiencies and reduce toxicities, but wide acceptance is still decades away.  It is unlikely that increases in technology can provide more than 1 to 2% annual average increases in efficiency and resource productivity [ need ref ]. 

Existing technologies are not likely to simply be abandoned even if these sustainable alternatives were readily available.  At best, there will be a transition period which will take decades to both optimizes the investment in existing technologies, and implement the infrastructure for new technologies.  It is therefore unlikely that technological innovation toward sustainability will keep pace with population increase over the next few decades.

A Sustainable Scale Perspective on Population
What is clear from a sustainable scale perspective is that:
Sociopolitical Implications
Making the overpopulation and over consumption combination even worse is the effect of “demographic fatigue” [GLOSSARY] faced by governments in developing areas that are overburdened and unable to cope with providing for the needs of their increasing populations (Brown, Gardner and Hailwel, 1998). According to the most recent UN calculations, the governments  of Afghanistan, Burkina Faso, Burundi, Chad, Congo, the Democratic Republic of Congo, East Timor, Guinea-Bissau, Liberia, Mali, Niger and Uganda are already incapable of meeting basic food and housing needs. Populations in each of these countries are expected to triple by 2050. At this time, a predicted 7.8 billion people will live in developing nations (UN report 2004).
1. Barlow, 2001.
2. PAI, 2000
3. Millennium Ecosystem Assessment. Ecosystems and Human Well-being. Washington: Island Press, 2003.
4. PAI, 2000
5. ref??
6. Cohen, p. 40
7. need ref
8. Brown, Gardner and Hailwel, 1998
9. UN Report 2004

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