A brief history of “IPAT” (impact = population
x affluence x technology)
John
P. Holdren
The following is a previously
privately circulated explanation of IPAT written by John Holdren in 1993 and
published here with permission as an appendix to Paul Ehrlich’s book review
(Vol.2 No.2 pp.63-65).
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DOI: 10.3197/jps.2018.2.2.66
Licensing: This article is Open Access (CC BY 4.0).
How to Cite:
Holdren, J.P. 2016. 'A Brief History of “IPAT”'. The Journal of Population and Sustainability 2(2): 66–74.
https://doi.org/10.3197/jps.2018.2.2.66
–––––––––––––––––––––––––––––––––––––––––––
In
late 1969, the then‑prominent biologist Barry Commoner began claiming in
speeches and lectures that he had sorted out the responsibility for the
environmental crisis and had found that neither population growth nor rising
affluence had much to do with it. The culprit, he said, was ecologically inept
choices of productive technologies in post‑World‑War‑2 industrial
societies. He often used the figure 95 percent in these talks to describe
the share of the “blame” for environmental problems attributable to faulty
technology. (The 95 percent claim is also made on page 176 of The Closing Circle,
the 1971 popular book through which his argument reached its largest
audience.) During 1970 Commoner published these claims in a variety of
unrefereed forums –Saturday Review,
Congressional testimony, and the like – and in April 1971 his more detailed
analysis, “The Causes of Pollution” (with Michael Corr and Paul J. Stamler)
appeared in Environment (1971/2010).
That journal was then the house organ of the Scientists’ Institute for Public
Information, which Commoner headed; I mention this because the transparent
errors of arithmetic and logic in “The Causes of Pollution” would have
precluded its publication in any competently refereed professional journal.
In
the Environment article, Commoner and co‑authors
offered up, with great fanfare, their discovery that
pollution = (population) x (production/capita) x
(pollution/production)
(an
intellectual achievement roughly equivalent to noticing that GNP equals
population times GNP per capita); and they proceeded to try – through a
combination of biased selection of data, redefinition of widely understood
concepts, and neglect of cause‑and‑effect relations, and with the help of major
mistakes in arithmetic – to support the proposition that 95 percent of the
problem resides in the last factor. These flaws survived unscathed the
expansion of the argument to 300 pages’ length in The Closing Circle,
which appeared later the same year and hammered home relentlessly the
simplistic message that neither population growth nor rising material
consumption is a major cause of environmental disruption. The culprit is
faulty technology, brought about by a faulty economic system. Here are
some quotes from The
Closing Circle (1971):
It
seems clear, then, that despite the frequent assertions that blame the
environmental crisis on ‘overpopulation’, ‘affluence’, or both, we must seek
elsewhere for an explanation. (Ibid. p. 139)
The
pattern of economic growth is the major reason for the environmental crisis. A
good deal of the mystery and confusion about the sudden emergence of the
environmental crisis can be removed by pinpointing, pollutant by pollutant, how
the postwar technological transformation of the United States economy has
produced not only the much‑heralded 126 percent rise in GNP, but also, at a
rate about ten times faster than the growth of GNP, the rising levels of
environmental pollution. (p 146)
[M]ost
of the sharp increase in pollution levels is due not so much to population or
affluence as to changes in productive technology. (Ibid. p. 177)
[The
technology factor] has a far more powerful effect on pollution levels than the
other two. (Ibid p. 211)
As it
happened, prior to Commoner’s initial revelation that population and affluence
are unimportant causes of environmental problems, I had started to collaborate
with Stanford biologist Paul Ehrlich on studies of more or less the same
questions –the interactions of population, poverty and affluence, technology,
and resource and environmental issues. (I was then a doctoral student at
Stanford in aeronautics and astronautics and theoretical plasma physics.)
Our first joint paper, “Population and Panaceas: A Technological Perspective”
(written in late 1968 and published in the refereed journal Bioscience in December 1969), showed why
technological “fixes” alone were unlikely to be able to cope with the pressures
posed by the combination of population growth and rising material
consumption. We were dismayed to learn, at a conference at the end of
1969, of Commoner’s determination to persuade people that population growth and
rising material consumption were nothing to worry about, and we began preparing
a rebuttal. It was presented as an invited paper to the President’s
Commission on Population Growth and the American Future in November 1970 and
was published in the 26 March 1971 issue of the refereed journal Science under the title “Impact of Population
Growth”. In it, we took the position that ALL of the factors (population,
affluence, technology, socioeconomic variables) are important, that they
interact, and that neglect of any of them, or of their interactions, is
dangerous. Here are some quotes from our paper:
Problems
of population size and growth, resource utilization and depletion, and
environmental deterioration must be considered jointly and on a global
basis. In this context, population control is obviously not a panacea –
it is necessary but not alone sufficient to see us through the crisis.
(3rd paragraph of the paper)
‘Environment’
must be broadly construed to include such things as the physical environment of
urban ghettos, the human behavioral environment, and the epidemiological
environment. (5th paragraph)
Complacency
concerning any component of these problems –sociological, technological,
economic, ecological– is unjustified and counterproductive. It is time to
admit that there are no monolithic solutions to the problems we face.
Indeed, population control, the redirection of technology, the transition from
open to closed resource cycles, and the equitable distribution of opportunity
and the ingredients of prosperity must ALL be accomplished if there is to be a
future worth having. Failure in any of these areas will surely sabotage
the whole enterprise. (conclusion of the paper; emphasis in original)
As
for the “IPAT” relation, Commoner’s version of the population‑production‑pollution
identity had not been published yet when we wrote the Science article, and we chose to present the
population‑impact relation in a way that stressed its inherent complexity from
the outset. Here is our initial treatment of the subject from Science of 26 March 1971:
The
total negative impact of an [agricultural or technological] society on the
environment can be expressed, in the simplest terms, by the relation
I = P * F
where
P is the population, and F is a function which measures the per capita
impact. A great deal of complexity is subsumed in this simple relation,
however. For example, F increases with per capita consumption if
technology is held constant, but may decrease in some cases if more benign
technologies are introduced in the provision of a constant level of
consumption…. Pitfalls abound in the interpretation of manifest increases
in the total impact I. For instance, it is easy to mistake changes in the
composition of resource demand or environmental impact for absolute per capita
increases, and thus to underestimate the role of the population multiplier.
Moreover, it is often assumed that population size and per capita impact are
independent variables, when in fact they are not. (Ibid. p.1212)
The
actual “IPAT” equation, using those symbols, appeared for the first time in the
critique of The Closing Circle that Paul Ehrlich and I wrote and
circulated widely in late 1971, and that was published together with Commoner’s
rebuttal in the April 1972 Environment and the May 1972 Bulletin of Atomic Scientists.
We introduced the “IPAT” version as a vehicle for illustrating the flaws in
Commoner’s use of the population‑production‑pollution identity, starting with
the problem that “pollution” is too narrow a concept for what is being done to
the environment (hence our preference for “impact”) and that “production” is
too narrow a term to capture the array of effects associated with rising
material well‑being (hence our preference for “affluence”). Here, in
full, is the passage from our 1971/72 critique of The Closing Circle in which the “IPAT” equation made its
first appearance in the literature:
Commoner
admits that the factors contributing to environmental impact are
multiplicative, rather than additive; he offers (in a footnote to pp 211‑212)
the equation
pollution = (population) x (production/capita)
x (pollution emission/production)
Here
the second factor on the right, production per capita, is in some sense a
measure of affluence, and the last factor, pollution per unit of production, is
a measure of the relative environmental impact of the technology that provides
the affluence. For compactness, let us rewrite this equation
I = P x A x T (1)
or,
in terms of initial values and the subsequent changes, over a specified period
of time,
I + delta I = (P + delta P) x (A + delta A) x (T + delta T)
(2)
Here
I is for impact (a better word than “pollution” for reasons already explained),
P is for population, A for affluence, and T for technology. Let us also
assume for a moment that the variables P, A, and T are independent; i.e., that
a change in P does not cause changes in A or T, and vice versa. We shall
find later that this is not true, but it is the simplest assumption and the one
most favorable to Commoner’s hypothesis.
It is
immediately obvious from equation (2), of course, that the actual magnitude of
the environmental deterioration engendered by an adverse change in technology
depends strongly both on the initial levels of population and affluence and on
such changes in these levels as may occur simultaneously with the change in
technology. A corollary is that population and affluence would be
important factors in environmental degradation even if they were not
growing. A change for the worse in the technology of production is more
serious environmentally if it occurs in a populous, affluent society than if it
occurs in a small, poor one. (Ibid. pp. 19-20)
We
went on, in the critique, to elucidate many of the ways in which the factors
are in fact causally interrelated, as well as showing how Commoner had mangled
the logic and arithmetic even for the hypothetical case when they are
independent. In our conclusion to this critique, we wrote:
In
fixing the blame for environmental deterioration on faulty technology alone,
Commoner’s position is uncomplicated, socially comfortable and, hence,
seductive. But there is little point in deluding the public on these
matters; the truth is that we must grapple SIMULTANEOUSLY with overpopulation,
excessive affluence, and faulty technology. (Ibid. p. 27, emphasis in original)
Unfortunately,
numerous writers revisiting “the population debate” in subsequent decades have
chosen to expound at length on the content and significance of this 1969‑1972
Ehrlich/Holdren/Commoner disagreement without, apparently, taking the trouble
to read any of the original documents. The result is passages like the
following (from an op‑editorial essay in Science of 25 June 1993 by National Academy of
Sciences staffer Paul Stern:
Scientific
progress has been slowed by a futile debate about which of these factors is the
most important driving force, a debate that rests on the erroneous assumption
that the contributions of these forces can be assessed independently. For
example, in decades of sharp debate about the impact of population growth on
the environment, some have argued that population growth is the primary cause
of environmental cause of environmental degradation (2), others that population
growth is environmentally neutral or even beneficial (3), and others that
population is secondary to technological or socioeconomic factors (4). (Stern 1993
p. 1897)
Under
note (2), Stern cites the 26 March 1971 Ehrlich/Holdren paper in Science (from which I quoted at length above),
as well as a 1974 Holdren/Ehrlich paper in American
Scientist, entitled “Human Population and the Global Environment”,
in which we are emphatic throughout that population, affluence, and technology
are ALL important, that the “IPAT” relation conceals much complexity, that its
component factors are causally interrelated and influenced by context, and so
on. Stern’s essay then goes on to inform the reader that:
What
has become clear is that the driving forces interact – that each is meaningful
only in relation to the impacts of the others and that the environmental
consequences of increased population are highly sensitive to the economic and
technological conditions of that population (7). (Ibid. p. 1897)
But
everything that Stern appears to think has only recently “become clear”(his
reference 7 being a 1992 National Research Council study for which he was the
staff director) was in fact already clear – and clearly stated in the
literature Stern misportrays – when Paul Ehrlich and I were writing about it in
1971. Evidently Stern has not acquired the scholarly habit of reading the
works he cites.
He is
not alone. As another example, consider the 1992 article by World Bank
analyst R. Paul Shaw on “The Impact of Population Growth on the Environment:
The Debate Heats Up” (1992). Shaw writes that the “IPAT” equation was “proposed
by Paul and Anne Ehrlich in 1990” (Ibid. p. 29), characterizes their position
as being that population growth “is largely responsible for global
environmental degradation”, and cites with an apparent sense of discovery and
approval the 1988 (re)statement by “leading environmentalist Barry Commoner”
that “The theory that environmental degradation is largely due to population
growth is not supported by the data” (Ibid. p. 11). The rest of Shaw’s
analysis is at a comparable level.
Consider,
finally, a paper entitled “Population, Environment, and Development: Key Issues
for the End‑of‑Century Scenario”, presented by Brazilian analyst George Martine
at a 1992 international conference on environment and development.
Martine writes:
A
sizeable segment of the existing literature on population and environment has
attempted to grapple with the intricacies of the theoretical interrelationships
between environmental change and what appears to be a restricted list of
variables: technology, population size, characteristics, and growth,
consumption levels and patterns. These relationships are customarily
summarized in the formula:
I (impact) = P (pop.) x A (affluence) x T (technology).
In
reality, however, the relationships between population size, consumption, and
technology are much more complex than suggested in this formula. [1]The heated
debates which have ensued within what appears to be a relatively limited number
of variables can be partly attributed to this complexity, as well as to
divergences of a theoretical‑ideological character. Inspiration for
different stances has come from a gamut of contrasting positions ranging from
Malthusian to Marxist to neo‑classical. Lack of hard data compounds the
absence of consensus on appropriate methodological approaches and added fuel to
the debate. What’s worse, all of the different positions are correct,
when examined from their own relative standpoints. [2] (Martine, 1992)
Under
note [1], Martine refers the reader “for a more general discussion” to Paul
Harrison, The Third Revolution:
Environment, Population, and a Sustainable World (1992).
In that book, Harrison struggles with the complexities of “IPAT”, clearly
handicapped by having read and talked to only Commoner on the subject, and gets
some of it right and some of it wrong. He accuses Ehrlich of lack of
precision – not realizing, having not actually read the relevant literature,
that it is Ehrlich AND Holdren he means to be (incorrectly) accusing – and he
credits Commoner with “the seminal work” in the field. He ends up saying,
with Martine, that EVERYBODY is more or less right. In note [2], Martine
(op. cit.) quotes Harrison as suggesting helpfully that “to overcome partial
views, we treat our familiar three factors – population, consumption, and
technology – as the proximate, direct determinants of environmental use which
influence each other and are influenced by other factors.”
This
last “insight”, which it appears that Martine believes Harrison discovered in
1992 (and perhaps Harrison DID learn of it only then), is of course the
perfectly obvious position that Ehrlich and I took when we first wrote about
“IPAT” in 1971.
As
for the proposition that “all of the different positions are correct”, I must
insist that when one position holds that only technology is important and
another holds that technology, affluence, and population are all important,
both positions are NOT correct; the first position is wrong, and the second one
is right. Of course, Martine may be onto something when he writes that
the debate has been partly due to “divergences of a theoretical‑ideological
character”: Ehrlich and I hold to the theory that logical argument,
getting one’s sums right, and reading the references one cites are important
principles in intellectual life; some of the other people in the debate
evidently hold to the theory that these principles can be safely ignored.
Commoner,
B., Corr, M. & Stamler, P.J. 1971/2010. The causes of pollution, Environment: Science and Policy
for Sustainable Development, 13:3, 2-19, https://doi.org/10.1080/00139157.1971.9930577
Commoner,
B., 1971. The closing circle: nature,
man, and technology. New York: Alfred A. Knopf
Commoner,
B., 1972. On “the closing circle”: Response. Bulletin
Of The Atomic Scientists, May 1972, pp 17, 42-56.
Ehrlich,
P.R. and Holdren, J.P., 1971. Impact of population growth. Science, vol. 171,
26 March 1971, pp 1212-1217. (See also the longer version by the same
authors under the same title in Commission on Population Growth and the
American Future, Research
Reports, Vol.
III: Population, Resources, and the Environment, Ronald G. Ridker,
ed., US Government Printing Office, 1972, pp 365-377.)
Ehrlich,
P.R. and Holdren, J.P., 1972. One-dimensional ecology. Bulletin Of The Atomic
Scientists, May 1972, pp 16, 18-27. (A version of the same
article was published without the permission or proofreading of the authors in Environment, April
1972, pp 24-34.)
Harrison,
P., 1992. The Third Revolution:
Environment, Population, and a Sustainable World. London:
I.B. Tauris & Co. Ltd.
Martine,
G., 1992. Population, environment and
development: Key issues for the end-of-century scenario. Paper
presented at the Workshop
on Population Programme Policies: New Directions, organized by
UNFPA and NESDB, Chiang Mai, September, 1992.
Shaw,
R.P., 1992. The impact of population growth on the environment: The debate
heats up. Environmental Impact Assessment
Review, Vol. 12, pp. 11-36.
Stern,
P. 1993 A second environmental science: Human-environment interactions. Science, Vol 260,
June 25th 1993,
pp. 1897-1899