I am disappointed by Duncan Wallaces’s response (NEJ, October 2019) to the articles by Kurt Johnson (NEJ, April 2019) , Mark Diesendorf (NEJ, June 2019) and Haydn Washington (NEJ, July 2019), which drew attention to the environmental impacts of human population on a finite planet. The subtitle of Wallace’s article implies that we, two environmental scientists and an engineer/journalist, are misanthropes, i.e. haters of humankind. Wallace (and Bookchin whom he quotes extensively) have allowed labelling people and rhetoric to substitute for reasoned debate.
Wallace misunderstands the nature of the relationship I = PAT, implying that it’s just an arbitrary equation that we have misrepresented as a law of nature. He then dismisses it on the grounds that it is tautological. But I = PAT is more than an equation, it is identically true, as previously explained by this author (NEJ, June 2019): by the definitions of the terms on the right-hand-side, it simply says I = I. So it is a tautology and more, but this is its strength, not its weakness, because it doesn’t need empirical justification any more than 6 = 2 x 3. It is the rates of increase of each of the three factors that are determined empirically.
The disaggregation of environmental impact (I) into the three factors population (P), ‘affluence’ (i.e. economic activity per person) (A) and technology (T) is useful because each of these factors can be addressed by different strategies, as illustrated in my example from the energy sector (NEJ, June 2019).
Wallace goes on to liken the I = PAT identity to ‘the abstruse mathematics of mainstream economics’, yet the identity is no more abstruse than 6 = 2 x 3.
Wallace next argues that using the identity implies that humans are all ‘bad’, an emotive term that none of us alleged misanthropes used. Humans use energy, materials and land. Humans dump wastes into the environment. These are facts of life. Human impacts on the environment depend on the numbers of humans, their economic activity per person and the technologies they use. This is reflected in aggregate in I = PAT. This is consistent with the fact that some people are stewards of the environment, but the majority are destroyers. Collectively, we are doing enormous damage, as David Attenborough has pointed out.
P, A and T have their own drivers that must also be addressed, although they don’t appear explicitly in the identity. Population growth is pushed by the property and retail industries and governments that wish to boast about GDP growth. ‘Affluence’ is pushed by advertising. Dirty technology is pushed by vested interests such as the fossil fuel and chemical industries. All three factors are pushed by institutions and cultures.
Of course, alleviating poverty and inequity are important issues in their own right, but their impacts on the environment are dwarfed by those of the multinational mining, agriculture, finance and property industries.
Wallace concludes that ‘Environmental degradation is caused by human behaviour, not population numbers’. However, the environmental impact of human behaviour depends on the number of humans, their economic activity per person and their choice of technologies, as expressed in I = PAT. Yes, we should change our behaviour, but this must involve addressing all these three factors and, I would add, changing our values. But we should not delay action on the immediate drivers of environmental impact until such time as we have an equitable, poverty-free society where everyone follows strong environmental ethics.