This article is a response to Dr Mark Diesendorf’s article ‘Population is a Driver of Environmental Impact: a Response to Duncan Wallace’ (NEJ, May 2020)
Thank you to Dr Mark Diesendorf for his reply.
He said that I implied, in my original article, that he and others are misanthropes. I don’t think I implied that any individuals were misanthropic – but I did say that the equation, I=PAT, has misanthropic presumptions. In the spirit of reasoned debate, I assume people are not misanthropes, and, if it can be demonstrated that a theory they subscribe to has misanthropic presumptions, I assume that’s something they’ll be concerned about.
I maintain that I=PAT has misanthropic presumptions. Here is why.
Mark Diesendorf says that I=PAT is tautologically true, and “doesn’t need empirical justification any more than 6 = 2 x 3”.
I=PAT is not a purely logical equation in the way 6 = 2 x 3 is. While a purely logical equation doesn’t need empirical justification, it does nevertheless require proof – a logical proof – which is what the study of mathematics is about.
Some equations are not purely logical, but purport to say something about the nature of the world. An example is E = mc2. This is an identity, but it nevertheless needs empirical justification given it claims to explain how the world works. As a scientist involved with a recent empirical test of E = mc2 said,
In spite of widespread acceptance of this equation as gospel, we should remember that it is a theory. It can be trusted only to the extent that it is tested with experiments”
I=PAT is like E = mc2: if it is to claim utility, it needs empirical justification.
Let me explain why I believe this is the case:
In the equation I=PAT, each term in the equation has a lower bound of zero.
This means that Impact must necessarily be at or higher than 0:
Thus, an empirical test of IPAT must demonstrate that Impact (I) is necessarily a positive value. If it can be shown that Impact (I) can be a negative value, then IPAT is not empirically justified.
Is there a way that Impact (I) could be a negative value? If it could have a negative value, this would mean that humans not only do damage, but can also be creators. We can think of this in terms of give and take – we are all givers and takers. A tree in a forest takes up resources for itself – it is a taker – but it also provides resources and services to other entities in its ecosystem. It is also a giver.
Humans are also, of course, not just consumers of ecosystem resources, but also providers of ecosystem services. Indeed, each of us are ourselves ecosystems of bacteria – more of the cells in our body are bacterial than are human. It is not hard to demonstrate the innumerable other ways humans provide ecosystem services – not least providing food for worms after we die (the circle of life)!
We do much more than provide food for worms though – we are a part of ecosystems, not dominant over them. Take, for example, the Amazon Rainforest. A journal article published in Science in 2011, with over 40 co-authors, found that the “region’s ecology is a product of 8,000 years of indigenous agriculture”. One of the leaders in the study said we should stop speaking about the Amazon as “pristine”. The Amazon, in fact, was shaped by humans: “human societies increased the abundance and distribution of useful species”, she said. “Perhaps”, said another of the co-authors, “the very biodiversity we want to preserve [in the Amazon] is not only due to thousands of years of natural evolution but also the result of the human footprint. The more we learn, the more the evidence points to the latter.”
We do not live outside ecosystems, having only impacts on them – we are part of them, and not only taking benefits from them, but contributing ecosystem services too. If that was not true, we would have to reject as impossible projects like regenerative agriculture.
(As an aside, a documentary series that is extraordinarily insightful in this regard, is the BBC’s Unnatural Histories).
Returning to I=PAT – if the above has any truth to it at all, PAT can only be one part of the equation – the part representing the fact that human beings take from our environment. It fails to represent the fact humans also give – it cannot account, for example, for a person planting a tree. Planting a tree cannot be accounted for by ‘Affluence’ (A), nor ‘Technology’ (T). Hence we must also recognise another part of the equation – let us call it PSG. This is the part that recognises that humans are also givers – that they perform ecosystem services; that they plant trees. That is:
|Population (P)||≥ 0|
|Services (S) (provision of ecosystem services)||> 0|
|Technology (G) (how effective we are at performing services)||> 0|
Here, we call technology G, to differentiate service technology from affluence technology, which is called T. So, our new equation for “Impact” is:
|Impact||= PAT – PSG|
|= P(AT – SG)|
This now allows Impact to be a negative value, if SG > AT (though, of course, it may very well be positive – it depends on how we behave!).
By this new identity, there is now no necessary relationship between population size and impact on the environment, given that it is recognised each person may be performing more ecosystem services than the total of the resources they are consuming. At issue is not the size of P, but whether AT is bigger than SG.
Of course, if humans are behaving in such a way that AT is out of balance with SG, then the size of P is relevant. But whether AT is bigger than SG, or visa versa, will depend on the society in question, and will not be uniform geographically or across time.
A further observation: so far, environmental scientists have been focussed on discovering the value of PAT, having assumed that this is equal to impact. However, PAT does not in fact equal I:
|Impact||= PAT – PSG|
|Impact + PSG||= PAT|
We see here that if we ignore the ecosystem services human beings engage in, and focus only on our consumption, we will have a warped understanding of our net impact. If we work out only the value of PAT, it will appear as if our Impact is larger than it is, since we are not working out our net Impact, but are instead working out our net Impact plus the sum total of our ecosystem services: Impact + PSG.
In addition to misleading us about the size of our net impact, I=PAT also blinds us to the fact that we not only need to minimise the harm we cause to environments, but we also need to start ramping up the ecosystem services we perform. It blinds us to what is perhaps our most important defence against ecological destruction – that is, our ability to positively enrich our environment. We cannot just focus on conservation – we must also focus on regeneration.
This demonstrates, if nothing else, that I=PAT requires empirical justification. Advocates of the utility of I=PAT must show empirically that it is to be preferred to, for example, I=P(AT–SG). If they cannot show that, they cannot claim any utility for I=PAT.
I think that I=P(AT–SG) may be better justified empirically than I=PAT. I=PAT, after all, assumes we are all “takers” but never “givers”, which is demonstrably not true. Hence my characterisation of I=PAT in my original essay as misanthropic: I described the equation as assuming all human actions are necessarily “bad” (Diesendorf has pointed out that is an emotive term, so in this reply I have gone for the term “take”, in the aforementioned sense of “give and take”, instead of “bad”).
Nevertheless, while better than I=PAT, I do not claim that I=P(AT–SG) is empirically useful. I think it’s just too hard to put a numerical value on things like affluence or ecosystem services. Also, the way that people interact together creates emergent properties, which cannot be captured by a linear equation.