Population and environment: a reply


By Mark O'Connor

The comment by Peter Boyle in the November 11 Green Left contained some serious misinformation about Paul Ehrlich's important I=PAT equation.

This equation indicates that for a given country or region — with the behaviour patterns and technology it has at a given time — I = P x A. That is, Impact on resources and environment = population size multiplied by average impact/consumption per individual. Clearly governments should work to hold down both of these multiplying factors. It makes no sense to pretend that only one of them is important.

In "cross-technology" comparisons, Ehrlich adds a third multiplying factor, T, for the destructiveness of the technology used to supply an average unit of consumption. Hence I = PAT. For example, if a given number of people P is to be supplied with an average of so many units of electricity per person A from a coal-burning station, then the carbon dioxide emissions might double if brown coal rather than black coal has to be used (in this case, T=2).

Thus the full form of this very useful equation is I=PAT. Yet in many contexts it can be simplified to I=PA.

Despite Peter Boyle's casual rhetoric, this equation is well respected. As Dr Alan Jones and Dr Tim Flannery, senior scientists at the Australian Museum, have pointed out, its truth is nearly self-evident, except in those cases where significant economies or diseconomies of scale may be involved.

Boyle is wrong to imply that I=PA can only be applied to macro situations. Certainly the equation World Environmental Impact = World population x Average per capita Environmental Impact is a crude one, because its second term must average out large differences between rich and poor. But I=PA can just as well calculate something as precise as the total electrical energy needed if battery-powered wheelchairs were supplied to all 53 nonagenarians currently living in East Brighton. It is like one of those fractal equations that can generate a model of a coastline equally on the broadest global scale or in almost microscopic detail.

Peter Boyle also complains that emphasis on I=PA "distracts" us from "the present inequitable world order" and "scapegoats" population growth. Not so. Per capita consumption (A) is one of the equation's two basic

multiplying factors.

In fact a great advantage of I=PA is its clarity on this issue. Anyone with Year 7 maths can readily grasp that if two factors are to be multiplied together, then clearly each is equally important. Yet if the interaction of population and consumption is explained in non-mathematical language, it is usually not too long before some confused soul is heard arguing "Of course it's not the number of people in Australia (or in Melbourne, or on the Earth) that damages the environment: it's how they choose to consume".

In fact the I=PA(T) equation is a good way to make the point Peter Boyle is bursting to emphasise: that each extra person added to the First World uses up to 30 times the energy resources of a person added to the Third World. This is precisely why groups like Jenny Goldie's Australians for an Ecologically Sustainable Population (AESP) and the ZPG and Negative Population Growth societies in the USA are trying to get people to have fewer children. Overpopulation is not just "over there" — it is right here in our own families. Boyle should perhaps study the account of I=PAT in AESP's very interesting document Future Directions for a Sustainable Australia.

One great value of I=PAT is that while it does not exaggerate the importance of population, it does force us to face the obvious: any large increase in population greatly increases the difficulty of achieving sustainability.

This is important because, as Professor Jonathan Stone pointed out recently on Occam's Razor, many people have trouble — indeed many environmentalists have trouble — accepting that humanity itself can be a problem. As Stone remarks, most people do not invent moral systems, they inherit them; and almost all of our traditional moral systems are based on valuing other human beings. Many people are genuinely frightened and confused by the suggestion that people themselves can become a plague; they fear that to admit as much will be to topple over some abyss into intolerance and bloody-mindedness.

In this respect the old fashioned communist's obsession with attributing all woes to inequality between classes of humans is as much an example of "the human exuberance and exultance" syndrome as the pope's view. (Even today some supposed greenies are closer to being lightly recycled reds with a green tinge.) Such persons tend to downplay the population problem. They often claim that their own intense agenda of pressing for a more equal distribution of wealth is the best or even the only way to prevent environmental damage — even with a constantly expanding population. Once again, I=PA can help remind us all that both terms matter. Trying to do without

one of them is like trying to walk on the left leg only.

And for those who are resolutely non-mathematical? Well, the answer to Boyle's insistence on emphasising problems of equity rather than problems of population can be put another way:

Yes, issues of equity and distribution do matter very much. They must be addressed as well as but never instead of environmental and population ones. It is not true that population growth doesn't matter because there is some superior system of distribution that "we" could introduce tomorrow if only we were not so wicked or foolish.

If all the world's wealth were distributed equally tomorrow human overpopulation would still be a deadly problem — to us and to every other species on earth. Even the world's 1985 harvest, its richest to date, could provide what the UN considers a fully adequate diet only for about 5 billion people. We are already five billion and heading on towards 10.

To argue that we should not worry much about overpopulation until we achieve global equity would be uncomfortably like arguing we shouldn't worry about road safety or about helping road-accident victims until every person in the world has equal access to a motor car — both a logical fallacy and a distraction.