Continuing our examination of the misuse (deliberate or not) of numbers and statistics by advocates of the “too many people” explanation of environmental destruction.
Part One showed that the global population numbers frequently quoted by populationist authors conceal immense differences between countries. The principal conclusion was that вЂњCO2 emissions are a problem of rich countries, not poor ones.вЂќ This means that programs that seek to mitigate global warming by reducing birth rates in poor countries are at best misguided.
Now we look at the misuse of вЂњper capitaвЂќ statistics. 
See also Part One: Population Where?
In an official briefing, the largest and most influential populationist group in the world explains why it favors a вЂњpopulation-based climate strategyвЂќ:
вЂњThe most effective national and global climate change strategy is limiting the size of the population. вЂ¦ A non-existent person has no environmental footprint: the emissions вЂsavingвЂ™ is instant and total.
вЂњGiven an 80-year lifespan and annual per capita emissions (2006) of 9.3 tonnes of CO2 вЂ¦ each Briton вЂforegoneвЂ™ вЂ“ each addition to the population that does not take place вЂ“ saves 744 tonnes of CO2.вЂќ
The UK-based Optimum Population Trust (OPT) goes on to quantify the lifetime saving from preventing one birth at ВЈ30,000 вЂ“ a вЂњnine million per centвЂќ return on a 35-pence investment in condoms.
We might view that as a feeble attempt at humor, had OPT not published a clearly serious study in August 2009, purporting to prove that birth control is the most cost-effective way to reduce carbon emissions. The methodology involved forecasting the number of unwanted births that might be eliminated between now and 2050 if modern birth control were universally available вЂ“ and then multiplying the number of non-people by the current per capita emission rates in the countries they wouldnвЂ™t be born in. Result вЂ“ 34 fewer gigatonnes of CO2, at a cost of only $7/tonne.
Prominent US populationist Lester Brown made a similar calculation to confidently predict that if the worldвЂ™s population by 2050 matches the UNвЂ™s вЂњlowвЂќ projection instead of the вЂњmediumвЂќ projection, we will reduce our energy needs by the equivalent of 2,792 million tons of oil. He arrived at that improbably precise figure by multiplying the difference between the two population projections by per capita energy use.
OPT, Brown, and the many others who make similar use of per capita emissions figures, are using an argument that seems to have originated with Paul and Anne Ehrlich, for forty years the worldвЂ™s most persistent and influential promoters of populationism. Their 1968 book The Population Bomb is the best-selling book on environmental issues of all time, and to this day itвЂ™s rare to find a magazine article on population that doesnвЂ™t cite or interview them.
In 1970, the Ehrlichs published a college-level text book whose central premise was set out in the Introduction: вЂњThe explosive growth of the human population is the most significant terrestrial event of the past million millennia. вЂ¦ Spaceship Earth is now filled to capacity or beyond.вЂќ 
They tried to express their views mathematically:
вЂњIt is axiomatic that the total impact of a society on the ecosystem can be expressed by the relation
I = P*F
вЂњWhere I is the total impact, P is the population size, and F is the impact per capita.вЂќ 
For F, you can substitute вЂњper capita emissionsвЂќ or вЂњecological footprintвЂќ or any other term that purports to measure individualsвЂ™ effect on the environment. Then, according to the formula, one personвЂ™s impact will be 1 times F, two peopleвЂ™s impact will be 2 times F, and so on.
Although longer versions of the formula have been proposed, this one is still widely used, both in narratives like the OPT statement quoted above, and in formal demographic studies. 
The median isnвЂ™t the message
At first glance, I = P*F appears obvious and undeniable вЂ“ thatвЂ™s why it remains central to populationist arguments. But its apparent simplicity conceals a common error: it mistakes an abstraction (an average or median) for concrete reality.
To illustrate this, we can turn to another field entirely. In 1982, the noted evolutionary biologist Stephen Jay Gould discussed his reaction to learning that he had a type of cancer for which the median survival time was just 8 months. His article was titled, profoundly, вЂњThe Median IsnвЂ™t the Message.вЂќ
вЂњWe still carry the historical baggage of a Platonic heritage вЂ¦ with its emphasis in clear distinctions and separated immutable entities, leads us to view statistical measures of central tendency wrongly, indeed opposite to the appropriate interpretation in our actual world of variation, shadings, and continua.
вЂњIn short, we view means and medians as the hard вЂrealities,вЂ™ and the variation that permits their calculation as a set of transient and imperfect measurements of this hidden essence. If the median is the reality and variation around the median just a device for its calculation, the вЂI will probably be dead in eight monthsвЂ™ may pass as a reasonable interpretation.
вЂњBut all evolutionary biologists know that variation itself is nature’s only irreducible essence. Variation is the hard reality, not a set of imperfect measures for a central tendency. Means and medians are the abstractions.вЂќ
Instead of despairing, Gould set out to learn how survival times varied concretely, and to find how he could maximize his chances of living longer than the вЂњmedian.вЂќ In fact, he lived 20 more years. 
The populationist equivalent of вЂњThe median survival time for people with my kind of cancer is 8 months, so in 8 months IвЂ™ll be dead,вЂќ is: вЂњCanadaвЂ™s per capita emission rate is 17.2 tonnes, so reducing the population by one will cut emissions by 17.2 tonnes.вЂќ
Measures such as вЂњemissions per capitaвЂќ or вЂњecological footprintвЂќ are created by dividing a countryвЂ™s total population into the total emissions generated in that country, or the total resources used there, or something similar. For comparing countries, a per capita figure can be more meaningful than a total вЂ“ for example, the usual media assertion that China is the largest emitter of greenhouse gases conceals the fact that China has over four times the population of the number two country, the USA.
But per capita statistics can be very misleading if we forget that they are abstractions and treat them as concrete measures of the impact of individuals on the environment.
Just as GouldвЂ™s median survival time concealed a great range of possible outcomes, so per capita emission rates (or any other form of pollution per capita) conceal great variations in the pollution that can actually be attributed to specific persons or groups.
Perhaps the most obvious problem is that a large proportion of green house gas emissions are not caused by individual behavior at all. Simon Butler and I made this point in a recent article about claims that reducing immigration will reduce emissions.
вЂњmost emissions are caused by industrial and other processes over which individuals have no control.
вЂњIn Canada, for example, no change in the number of immigrants will have any effect on the oil extraction industry at the Alberta Tar Sands, described by George Monbiot as вЂthe worldвЂ™s biggest single industrial source of carbon emissions.вЂ™
вЂњReducing immigration to the United States will have no effect whatsoever on the massive military spending вЂ“ up 50% in the past decade вЂ“ which ensures that the Pentagon is the worldвЂ™s biggest consumer of oil. вЂ¦
вЂњClosing AustraliaвЂ™s borders would have had no effect on the climate denial policies of the previous Liberal Party government, or on the current Labor governmentвЂ™s determination to continue AustraliaвЂ™s role as вЂthe worldвЂ™s largest вЂcoal mule.вЂ™вЂќ
Reducing immigration wonвЂ™t change any of those things, nor will reducing the population by other means. In fact, reducing population is more likely to have the paradoxical effect of increasing per capita emissions вЂ“ proving once again that this statistic is an abstraction.
So at the very least, before claiming to predict the emission saving that will result from preventing one or a hundred or a million births, OPT should calculate a per capita figure that only includes emissions that are caused directly by individuals.
But even that wouldnвЂ™t make per capita emissions a useful guide to the effect of increasing or decreasing population. It may improve the numerator (emissions), but it still uses a denominator (population) that, as Marx wrote, is itself an abstraction.
According to an old joke, if you stand with one foot in the oven and the other in the freezer, on average youвЂ™re reasonably comfortable. ThatвЂ™s exactly the problem with вЂњper capitaвЂќ вЂ“ itвЂ™s an average that conceals inequalities within the population.
A study published by the Canadian Centre for Policy Alternatives illustrates this. Drawing on path-breaking research by a former Director at Statistics Canada, Size Matters вЂњfinds that the ecological footprint of high-income Canadian households is substantially greater than that of everyone else.вЂќ
вЂњThe richest 10% of Canadian households are leaving behind an ecological footprint of 12.4 hectares per capita. To put that finding in context, their per capita ecological footprint is 66% higher than the national average. вЂ¦
вЂњThe ecological footprint of the richest 10% of Canadians is nearly two-and-a-half times that of the poorest 10%.вЂќ 
The average ecological footprint increases gradually from 5.03 hectares in the poorest group to 8.87 hectares for those just below the top вЂ“ and then it jumps by 40% to 12.42 hectares for those in the top 10%. As a CCPA news release announcing the report says, вЂњWhen it comes to environmental impact, it really is a case of the rich and the rest of us.вЂќ 
Canada is not unique. A survey of household GHG emissions in India found even more extreme disparities вЂ“ вЂњthe highest income group in India, constituting merely 1% of the population, emits four and a half times as much CO2 as the lowest income group consisting of 38% of the population.вЂќ A presentation accompanying that study concluded:
вЂњThere is no average India but a major divide between the emissions between the CO2 emissions of the rich and the poor.вЂќ 
Global Inequality vs Per Capita Pollution
In The Political Economy of the Environment, James K. Boyce considers the impact of global inequality on the environment, comparing the wealth not of countries but of people. He cites 1988 UN figures showing that the richest 20% of individuals in the world had average incomes of $22,800 each, while the poorest 20% averaged $163 each вЂ“ a 140 to 1 ratio. He concludes:
вЂњThe amount of environmental degradation associated with a dollarвЂ™s worth of production and consumption is likely to vary across individuals and countries.
вЂњWhether degradation per dollar is higher for poor people or for rich people is a question on which little systematic evidence has been collected. If the amount of degradation per dollar were roughly the same for both groups, the richest 20 percent of the worldвЂ™s people would account for 140 times as much environmental degradation as the poorest 20 percent.
вЂњPut differently, the total amount of degradation for which the poorest fifth is responsible could equal that for which the richest fifth is responsible only if the degradation per dollar for the poor were 140 times greater вЂ“ a rather implausible suggestion.
вЂњThis simple comparison suggests that environmental degradation driven by the economic activities of the rich is likely to surpass, by a substantial margin, that driven by the economic activities of the poor.вЂќ 
The gap between rich and poor has expanded since 1988. In 2005 Thomas Pogge of Columbia University reported that the income ratio between the richest 10% of the worldвЂ™s population and the poorest 10% was 320 to 1. This makes BoyceвЂ™s conclusion even more credible today.
This gap is, inevitably, reflected in access to birth control: According to leaders of International Planned Parenthood, вЂњIn every country for which we have data, women in the highest quintile [richest 20%] have much better access to contraceptives when compared with the lowest quintile.вЂќ 
Despite this, groups such as Optimum Population Trust and the Sierra ClubвЂ™s Population Justice Project claim that future Third World emissions can be significantly reduced by meeting вЂњunmet needsвЂќ for birth control вЂ“ that is, by providing reproductive health services to the worldвЂ™s poorest people, who have the least access to birth control, who cause the least environmental damage today, and whose children are the least likely to contribute to increased emissions in coming decades.
As noted demographer Wolfgang Lutz has pointed out:
вЂњwithin each country the rich have fewer children and emit significantly more than the poor. India, for example, has a per capita carbon emission of only 0.21 tons. Although this is one of the lowest in the world there is every reason to assume that the richest 10 percent in India emit at least 10 times more than the bulk of the population and that the expected future population growth of India comes almost entirely from the poor segments of the population. If this is true, the actual impact of population growth on carbon emission will be much less than national averages would imply.вЂќ 
We can restate his final sentence:
Reducing the number of babies born to poor women in India will have much less actual impact on carbon emission than national averages (per capita emission numbers) would imply.
A 2009 study of the impact of global inequality on green house gas (GHG) emission levels, by Dr. David Satterthwaite of the UKвЂ™s International Institute for Environment and Development, found that вЂњa significant proportion of the worldвЂ™s urban (and rural) populations have consumption levels that are so low that they contribute little or nothing to such emissions.вЂќ
Among his conclusions:
вЂњIt is very misleading to discuss responsibility for GHG emissions per person using national averages because of the very large differences in per capita emissions within each nation between the highest-income and lowest income groups вЂ“ perhaps a 100-fold or more difference between GHG emissions per person if we could compare the wealthiest 1 per cent and the poorest 1 per cent in many nations вЂ¦
вЂњIf GHG emissions were allocated to people (not nations) on the basis of the contribution of their consumption to GHG emissions, it is likely that the wealthiest one-fifth of the worldвЂ™s population would account for more than 80 per cent of all GHG emissions (they have more than 80 per cent of the worldвЂ™s income) and an even higher proportion of historical contributions to GHG emissions. The consumption of the one fifth of the worldвЂ™s population with the lowest income levels may account for only around 1 per cent of all GHG emissions.вЂќ 
Part One of this article dissected the global population numbers that populationists so often cite, and concluded that CO2 emissions are a problem of rich countries, most of which have low birth rates, not poor ones with high birth rates. This means that the often-claimed correlation between global population growth and global warming is an illusion.
In Part Two, weвЂ™ve seen that per capita numbers, which are also used to support populationist conclusions, conceal substantial inequalities within populations and between people. When we dissect the numbers, we find that mostemissions and pollution cannot be attributed to the actions of individuals, and that insofar as some can be, they are mainly caused by rich people, not poor ones. This means that using ’per capita’ numbers or national averages to calculate the environmental impact of population changes will produce misleading results. (In short: I=P*F is wrong.)
So far, we have focused on quantitative issues вЂ“ the differences in income or emissions between rich and poor. A unconvinced populationist could now reasonably respond: Yes itвЂ™s true that rich countries and rich people produce more emissions and other forms of pollution. But all people produce some, so any reduction in population will reduce the problem.
The ecosocialist response to that objection is that those overpopulation numbers donвЂ™t just conceal quantitative inequalities вЂ“ they conceal qualitative differences of class and power.
WeвЂ™ll discuss that subject in Part Three.
To be continued
 Judging by some of the responses I received to the first article in this series, I should point out that disagreeing with the analysis and solutions proposed by populationists is not the same as believing that the worldвЂ™s resources are infinite, or that economic growth can continue forever, or that population size is irrelevant. As someone said, вЂњSaying that IвЂ™m not at the South Pole does not mean that I am at the North Pole.вЂќ
 “A Population-Based Climate Strategy – An Optimum Population Trust Briefing.” Accessed May 26, 2010 at http://www.optimumpopulation.org/opt.sub.briefing.climate.population.May07.pdf
 Thomas Wire. Fewer Emitters, Lower Emissions, Less Cost: Reducing Future Carbon Emissions By Investing in Family Planning. Accessed May 26, 2010 at http://www.optimumpopulation.org/reducingemissions.pdf
 Lester Brown et al. Beyond Malthus: Nineteen Dimensions of the Population Challenge. WW Norton, New York 1999. p. 47
 Paul R. Ehrlich and Anne H. Ehrlich. Population Resources Environment: Issues in Human Ecology. WH Freeman & Company, San Francisco. Second Edition. 1972. pp 1, 3
 Ibid, p. 252. This is an early version of the IPAT formula: Impact = Population times Affluence times Technology. Although it contains more terms, IPAT is effectively identical to вЂ“ and has the same weaknesses as — its predecessor.
 See, for example, Brian OвЂ™Neill et al. Population and Climate Change. Cambridge University Press, 2001. p. 117.
 Stephen Jay Gould. вЂњThe Median IsnвЂ™t the Message.вЂќ Bully for Brontosaurus: Reflections in Natural History. WW Norton, New York, 1992. pp 473-478
 Ian Angus and Simon Butler. вЂњShould Climate Activists Support Limits on Immigration?вЂќ Climate and Capitalism, January 24, 2010. Accessed May 27, 2010 at http://climateandcapitalism.com/?p=1562
 Hugh Mackenzie, Hans Messinger, and Rick Smith. Size Matters: Canada’s Ecological Footprint, By Income. Canadian Centre for Policy Alternatives, June 2008. p. 5. Accessed May 27, 2010 at http://www.policyalternatives.ca/publications/reports/size-matters.
 Hiding Behind the Poor. Greenpeace India Society, October 2007. Report, news releases and presentation accessed May 28, 2010 at http://www.greenpeace.org/india/footer/search?q=Hiding+Behind+the+Poor
 James K. Boyce. The Political Economy of the Environment. Edward Elgar, Northampton, MA, 2002. p.6
 Summary of a discussion of the book Worlds Apart, sponsored by The Carnegie Endowment for International Peace, September 28, 2005. Accessed May 28, 2010 at http://www.carnegieendowment.org/files/Worlds_Apart_Discussion.pdf
 Carmen Barroso and Steven W. Sinding, вЂњCairo: The Unfinished Revolution.вЂќ Laurie Mazur, ed., A Pivotal Moment: Population, Justice, and the Environmental Challenge. Island Press, Washington, D.C. 2010. p. 250
 Wolfgang Lutz. “World Population Trends: Global and Regional Interactions Between Population and Environment.” In Lourdes Arizpe et al, eds. Population and Environment: Rethinking the Debate. Boulder: Westview Press. 1994. p. 59
 David Satterthwaite, вЂњThe implications of population growth and urbanization for climate change.вЂќ Environment & Urbanization. 2007 Vol. 21(2) p. 545
Study: UT system brings in $2.5BResponse to “Who’s to blame for the population crisis?” in Mother Jones