The Ehrlich-Holdren formula1, useful in quantifying the human environmental impact, has survived many rounds of critique. It states that the rate of total human environmental impact ‘I’ depends on the number of humans on Earth ‘P’, on the individuals’ affluence ‘A’, and on ‘T’, which is a measure of environmental damage caused by the production of one unit of consumed goods. The affluence is strongly correlated to the global average rate of resources consumed per person ‘xav’ and the T-factor depends on the kind of technology used in the production process:
I = P A T = P xav T = X T (1)
Where the total resource consumption ‘X’ is given by X = P xav. Today’s carbon based energy technology, and the energy intensive industrial scale agricultural technology are mainly responsible for a large T-factor. Barbara Zimmerman2 claims that agriculture contributes more to loss of rainforests than logging. Consumer attitudes, urbanization, and infrastructure have an impact on the T-factor of the equation.
Apart from the Technology factor it is often stated by politicians, academics and environmentalists alike that population does not matter much, consumption is the problem. Susan McDaniel3, says that the “Billionaire club” sees population growth as the big problem; this tends to shift responsibility from rich to poor (people and countries), following a long tradition of rich blaming poor for their reproduction. In support of this view, George Montbiot4 and David Satterthwaite5 point to the statistics, which in a simplified form indicate that at present 80% of world’s poor population consume only 20% of the resources, and 20% of the population consume 80% of the resources6. Pope Francis' encyclical letter Laudato Si' points in that direction as well7. The views that: population does not matter and that consumption is responsible for unsustainable civilization is widely accepted and considered politically correct. At face value, using today’s statistical data this view seems justifiable. However, its validity must be further investigated, because it clearly contradicts the Ehrlich-Holdren impact formula.
One of the problems of the population-does-not-matter view is that it ignores the imperative of global justice; it neglects to consider that the numerous poor have a legitimate claim to a higher standard of living. Global justice demands that the poor be allowed to consume more. Increasing consumption by the poor is in agreement with reducing poverty as proposed by the UN millennium goals8, and the proposed UN Sustainable Development Goals9, which see poverty eradication as the greatest global challenge facing the world today.
Using the Ehrlich-Holdren formula (1) and Data from the Global Footprint Network10, a quantitative relation can be established between sustainable population, global average resource consumption per person and the kind of technology used.
If today’s total resource consumption is X, which determines the global footprint, and if the Global Footprint Network data is correct, then today we are 50% beyond sustainability:
X = 1.5 Xs (2)
Xs is the sustainable global consumption of resources, when the world footprint is equal to the biological capacity of the Earth.
If we use the simplified 80/20 distribution of poverty and consumption, then
X = Pp xp + Pr xr = 0.8 P xp + 0.2 P xr = P xav (3)
Pp and Pr are the number of poor and of rich people, xp and xr are the resource consumption per person of the poor and the rich; xav is the global average resource consumption per person which is, from (3):
xav = X/P (4)
From the assumed data and equation (4) follows:
0.8 P xp = 0.2 X, or xp = 0.25 xav , and 0.2 P xr = 0.8 X, or xr = 4 xav (5)
This reflects the presently unjust use of resources. With today’s 80/20 consumption distribution the world average per person consumption is xav = 0.25 xr = 4 xp. Thus the rich use four times more and the poor four times less resources per person than the world average. This means that the few rich use 16 times more resources per person than the many poor. In an ideal just world everyone would use the same amount of resources. In reality, a just distribution of individual consumption would differ from the average due to climatic and other local conditions.
Keeping present day carbon based technology, the relation between a sustainable world population Ps and the resource consumption per capita xav is, with (2), (3), and (5):
Ps xav = Xs = X/1.5 = P xav/1.5 = P (0.25xr/1.5) = P xr/6, or:
Ps = (P xr/6)/ xav = (P/6) xr/xav (6)
The Global Footprint Network states, that carbon footprint is half of the total footprint. Therefore, the sustainable population can be doubled by changing energy technology to all renewable energy resources with zero carbon emissions:
Ps = (P xr/3)/ xav = (P/3) xr/xav (7)
A graph of how the sustainable population depends on the per capita consumption and on the kind of energy technology used is given in Figure 1.
Figure 1. Relation between sustainable world population and resource consumption. The vertical axis gives the sustainable world population in Billions as a function of the global average per capita consumption of resources xav as a fraction of present day per capita resource consumption xr in rich countries. The red series gives the sustainable population under today’s condition of mainly carbon based energy, the green series shows the sustainable world population for zero carbon, totally renewable resources based energy technology.
The following scenarios illustrate situations of interest.
1. Present Situation
The present population according to the world population clock is 7.3 billion. With today’s average per person resource consumption being 0.25 xr, equations (6) and (7) yield a sustainable population of 4.9 billion with carbon based energy and 9.9 billion with renewable energy
2. All Poor Scenario:
This is the unlikely case, where all humans would consume resources at the level of today’s poor, using just food near starvation and no machines, no carbon energy. In this case, with (5), the per-person consumption xav = xr/16. Therefore, with equation (7), in the all-people-poor scenario the Earth could carry sustainably 5.3 times the present population, i.e., 39 billion people.
3. All Rich Scenario
If the poor increase consumption and all humans were to consume at the level of today’s rich, then x = xr, and with (6) the sustainable world population is 1/6 of the present day population, i.e., 1.2 billion people with present day energy system, or 2.4 billion with 100% renewable resources based world energy system.
4. Contraction and Convergence
If the poor develop to a point where they double their resource use, and somehow the rich cut back to half of their present per capita resource consumption, the total consumption would be with (3):
X4 = 0.8 P 2 xp + 0.2 P 0.5 xr = 1.6 xp + 0.1 xr = 1.6 P 0.25 xav + 0.1 P 4 xav, or
X4 = 0.4 P xav + 0.4 P xav = 0.8 X (8)
The total resource consumption in the reasonable contraction and convergence scenario would be only 80% of today’s consumption and the global average per person consumption would also be lower: P x4av = 0.8 P xav , or x4av = 0.8 xav. The sustainable population at this per capita consumption is: P4 x4av = Xs, or with (2): P4 0.8 xav = (P xav)/1.5. Hence P4 = P/1.2. In this quite realistic scenario the planet could sustain 6.1 billion people with present day technology, and 12.2 billion with totally renewable energy.
5. Convergence and Sustainability
If the gap between rich and poor was closed, and all of today’s people would consume the same share of the sustainably available total resources Xs, then the average per person consumption in a just and sustainable world would be:
x5av = Xs/P = (X/P)/1.5 = 0.67 xav = 2.7 xp = 0.17 xr (9)
In a just world at today’s population and technology, the world average per capita consumption must be reduced to 67% of the present average per capita consumption, while according to (5) and (9) the poor could increase consumption by a factor of 2.7 and the rich would have to reduce consumption to 17% of their present consumption in carbon based energy. With renewable energy the results are that the poor could quintuple their consumption, and the rich need to reduce to some 40% of their present use.
6. Doubling Today’s Consumption
If all humans wished to live in a sustainable world at half the standard of living of today’s rich, i.e. average consumption per person in this scenario is with equation (5): x6av = 2 xav; in this scenario the sustainable population P6 is lower than the present world population:
P6 2 xav = Xs = X/1.5 = (P xav)/1.5, or: P6 = P/3 = 0.33 P = 2.4 billion (10)
This means that only one third of today’s population can be sustained if the global average resource consumption per person is half of what it is today in the rich nation. With renewable energy, 4.8 billion could be sustained at this life style.
The Impact of Justice on Lifestyles and Population
The fourth scenario describes a meaningful first step toward global justice. The poor double their consumption, and the rich cut their consumption in half. It turns out that under these conditions the Earth can sustain 6.1 billion people with present technology or 12.2 billion with renewable energy.
Achieving full justice by closing the gap between rich and poor, this means all humans have more or less the same level of consumption per person. In this case, there are two just and sustainable options. One is described in scenario five. It keeps the present population, and changes the lifestyle. The sixth scenario gives the example of a lifestyle characterized by half the level of consumption of today’s rich, then only 33% of today’s population i.e. 2.4 billion people can be sustained with carbon energy and 4.8 billion with renewable energy. In general, the sustainable population as it depends on the average per capita consumption is represented in Figure 1.
The illustrative scenarios clearly show the connection between consumption, lifestyle choices and population numbers. If the global footprint analysis is correct, then in a just and sustainable world at present population of 7.3 billion, humankind must reduce global resource consumption to 67% of the present resource consumption. Even with carbon based energy the poor could triple their consumption, the rich would have to reduce to less than 17% of their present consumption. If, for the sake of global justice, a higher standard of living for the poor is desired, the global average resource consumption per person will rise and sustainable population will accordingly be lower as shown in Figure 1. The UK based organization ‘Population Matters’ is right11.
A note of warning is appropriate. Today’s species extinction rate is given at 30,000 species per year12. Prorated to the sustainable level according to the global footprint analysis given in (2), still some 23,000 species a year are going extinct. The global footprint definition of sustainability does not sufficiently take the loss of biodiversity into account. Therefore, genuine sustainability does require more appropriate technology, lower average resource consumption per person, and much lower populations than those calculated here on the basis of the global footprint analysis.
1. P.R. Ehrlich and J. Holdren, The Impact of Population Growth, Science, Vol. 171, (1971) p.1212
2. Barbara Zimmerman, Director, Kayapo Project, Conservation International, Brazil Program, Washington DC.: oral communication at the University of Toronto Faculty of Forestry and Science for Peace Roundtable on Forestry, 22/23 September 2006.
3. Susan McDaniel, Director, Prentice Institute & Prentice Research Chair in Global Population & Economy & Professor of Sociology, University of Lethbridge, Alberta, private communication, 21 November 2009.
4. George Monbiot: The Population Myth, 30 September 2009.
5. David Satterthwaite of the International Institute for Environment and Development:
The implications of population growth and urbanization for climate change, 27 October 2009.
6. Adèle Meijer, A fair share in environmental space, Share International, 6 December 2009.
7. Pope Francis, Laudato Si', specifically paragraphs # 50 and # 95, 24 May 2015.
8. United Nations, Millennium Development Goals: 1990 to 2015, accessed 19 August 2015.
9. United Nations, Sustainable Develoment Goals: 2015 to 2030, accessed 19 August 2015.
10. Global Footprint Network, World Footprint, accessed 19 August 2015.
11. Optimum Population Trust, Population Matters for a Sustainable Future, accessed 19 August 2015.
12. Casey Kazan and Rebecca Sato, The Earth's 6th Great Mass Extinction is Occurring as You Read This, The Daily Galaxy, 26 February 2008. Based on The Creation: An Appeal to Save Life on Earth by Edward O. Wilson, W. W. Norton & Company, 17 September 2007.
ABOUT THE AUTHOR|
Helmut Burkhardt is Professor Emeritus of Physics, Ryerson University, Toronto, Canada. His early research was in thermonuclear fusion and magneto hydrodynamic energy conversion at the University of Stuttgart and at the University of Quebec. Later the focus was renewable energy research, general systems theory, substance accounting, sustainability, and global governance*. As Director of the Ryerson Energy Centre he organized many interdisciplinary conferences cosponsored by Science for Peace and the International Society for the Systems Sciences.
After retirement Helmut was co-founder and member of the Global Issues Project of Science for Peace and the Canadian Pugwash Group; the purpose of this project is a full-spectrum study of sustainability issues. He is a member of the American Association of Physics Teachers, a life member and past president of Science for Peace, and a member of the Canadian Pugwash Group, the Canadian World Federalist Movement, and the International Network of Engineers and Scientists for Global Responsibility.
* Good Global Governance For a Just and Sustainable World