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The ecological footprint: an exhibitat an intergenerational trial?
Gregory Ponthiere
Received: 16 February 2007 / Accepted: 23 November 2007 / Published online: 6 December 2007� Springer Science+Business Media B.V. 2007
Abstract This paper aims at assessing the extent to which the ecological footprint
indicator (EF) can be regarded as an exhibit allowing an intergenerational trial about the
use of natural resources. For that purpose, we examine various criticisms questioning the
relevancy of EF measures for the study of environmental justice between generations. We
explore the difficulties raised by the physical—and highly aggregated—nature of EF
measures, as well as problems related to the number, the possible non-existence, and the
tastes of future generations. The extent to which postulates on nature’s regeneration and
technological progress affect the significance of EF studies is also discussed. It is con-
cluded that those criticisms, by identifying various weaknesses of EF measures for the
study of intergenerational justice, point to several crucial refinements of existing EF-based
analyses.
Keywords Ecological footprint � Future generations � Intergenerational justice �Natural resources
1 Introduction
Introduced by Rees (1992) and Wackernagel and Rees (1996), the ecological footprint
indicator (EF) measures the surface of land and water required by an economy to produce
all goods consumed in that economy, and to absorb all wastes generated by their
Readers should send their comments on this paper to: [email protected] within 3 months of publicationof this issue.
G. Ponthiere (&)FRS-FNRS, CREPP, HEC-ULg, University of Liege (Belgium), Boulevard du Rectorat,9, Batiment B31, Sart-Tilman, 4000 Liege, Belgiume-mail: [email protected]
123
Environ Dev Sustain (2009) 11:677–694DOI 10.1007/s10668-007-9136-x
production.1 Thanks to its capacity to provide, by means of a single figure, a global picture
of human dependency on nature, the EF has become, during the last decade, increasingly
used by scientists studying the pressure put by human societies on the natural
environment.2
EF measures have been computed for various purposes, such as the comparison of the
dependencies of diverse regions on natural resources (see Bicknell et al. 1998; Wacker-
nagel et al. 2005). Other applications include the empirical estimation of the environmental
impact of various consumption goods (see Wiedmann et al. 2006), and the description of
possible future ecological scenarios (see van Vuuren and Bouwman 2005; Yue et al. 2006).
Besides those different applications, EF measures have been also computed to study
environmental justice between generations, that is, to make empirically grounded state-
ments about the fairness, with respect to future people, of the current depletion of natural
resources.
In order to evaluate the fairness of the current use of natural resources with respect to
future generations, EF measures are generally contrasted with bio-capacity estimates
(measuring the maximum supply of natural resources compatible with their reproduction).
That conventional use of EF measures is illustrated by Fig. 1, which compares, for the last
40 years, the evolutions of the world’s EF and the world’s bio-capacity.3
As shown by Fig. 1, the surface required by the production of the consumption basket of
the average citizen of the world has significantly grown over time, from about 1.6 global
hectares in 1961 to about 2.2 global hectares today. Moreover, given that bio-capacity has,
over the same period, fallen, a kind of ‘environmental deficit’ has appeared since the early
1980s, reflecting that the pressure put on nature exceeds the one allowing its reproduction.
Hence, if one adheres to a purely physical, resources-centred concept of sustainability, the
current use of natural resources appears to be unsustainable.
The EF, by allowing the comparison of the actual pressure put on nature with the
hypothetical pressure compatible with the reproduction of nature, can be used as an
‘exhibit’, making possible the existence, at least in theory, of an ‘intergenerational trial’.
Such a ‘trial’ would allow the defence of future generations’ rights, which seem, in the
light of EF figures, to be violated by the current use of nature. Hence, current generations
may be ‘condemned’ on the grounds of their excessive—and unfair—depletion of nature
revealed by EF figures.
However, although a priori well-founded, the above use of EF measures as a kind of
exhibit is not exempt from criticisms. Thus, it is far from obvious that EF figures can really
serve as a basis for the making of an intergenerational trial about the use of natural
resources.
The goal of this paper is to evaluate the capacity of the EF to serve as an exhibit at an
intergenerational trial, by examining the validity of the major arguments against such a use
of EF measures. In other words, the present study aims at investigating whether the EF
indicator can be regarded as having the ability to ground, on empirical facts, statements
about intergenerational justice as far as the use of natural resources is concerned.
1 The EF is measured in ‘global hectares’. A global hectare is an aggregated unit of measurement forsurface, in which all kinds of biologically productive areas are converted by means of equivalence factors(e.g. an hectare of pasture equals 0.5 global hectares; an hectare of forest equals 1.4 global hectares). SeeWackernagel et al. (2005).2 See, for instance, the Symposium on the Ecological Footprint in Ecological Economics (2000).3 Sources: Global Footprint Network, available online at http://www.footprintnetwork.org.
678 G. Ponthiere
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For that purpose, we shall abstract from several criticisms against EF measures, such as
the difficulty, in (circular) economies where millions of goods are produced by means of
millions of goods, to compute the surface required by the production of each of those goods
(see Bicknell et al. 1998). Moreover, we shall also abstract from EF’s anthropocentric
nature (see Venetoulis and Talberth 2007), and from interpretational difficulties raised by
the comparison of EF figures across countries (see van den Berg and Verbruggen 1999;
Ferguson 1999). Hence, this study aims at complementing the existing literature on the EF,
by examining its foundations as an indicator of environmental justice between generations.
This paper is organized as follows. Sections ‘The ecological footprint and resources-
centred sustainability’ and ‘The ecological footprint and the aggregation criticism’ review
several criticisms against the EF as an informational basis for the study of intergenera-
tional justice. Then, Sections ‘The ecological footprint and the different number problem’,
‘The ecological footprint and the uncertainty about future generations’ existence’, and ‘The
ecological footprint and the non-identity problem’ explore some problems related to futuregenerations—their number, their possible non-existence, and their tastes—in the context of
EF-based analyses. Finally, Sections ‘The ecological footprint and the knowledge of
nature’s regeneration’ and ‘The ecological footprint and the knowledge of technological
progress’ assess the extent to which difficulties to make forecasts on nature’s reproduction
and technological progress affect the usefulness of EF calculations. Section ‘Concluding
remarks’ concludes.
2 The ecological footprint and resources-centred sustainability
The status of the ecological footprint as an exhibit making an intergenerational trial possible
can be questioned by arguing that the EF constitutes a purely physical index, which, as such,
has little relevance for assessing the fairness of the actual depletion of nature.
That criticism, which was made, among others, by van den Berg and Verbruggen
(1999), can be formulated as follows.4 The EF indicator is, by definition, a physical index,
Fig. 1 World’s ecological footprint and bio-capacity, 1961–2002 [sources: Global Footprint Network (2005)]
4 Criticisms against the purely physical nature of the EF were also made by Ayres (2000), Moffat (2000)and van Kooten and Bulte (2000). For a defence, see Wackernagel and Silverstein (2000).
The ecological footprint: an exhibit at an intergenerational trial? 679
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which aggregates goods by weighting these not by market prices (which have, under some
assumptions, a welfare significance), but, rather, by their costs in terms of natural
resources. However, as van den Berg and Verbruggen (1999) emphasized, physical weights
do not necessarily coincide with social weights. Hence, given that EF measures have no
obvious relation with social welfare, using EF measures as a basis for assessing the fairness
of nature’s depletion is inadequate. Knowing how many global hectares are used to pro-
duce current generations’ consumption is useless, as this informs us neither on the welfare
that current generations derive from these, nor on the damages undergone by future
generations.
That criticism tends also to question the relevancy, for intergenerational justice, of
comparing the pressure put on nature with bio-capacity. Actually, once it is acknowledged
that the EF has no relation with social welfare, it is not obvious to see why one should, as
we did in Section ‘Introduction’, compare the actual EF level with its hypothetical level
maintaining the stock of natural resources constant. Is the constancy of the stock of natural
resources the ethical standard that is relevant for assessing the fairness of the current use of
resources?
Thus, van den Berg and Verbruggen’s criticism of the welfare foundations of the EF
tends also to question the significance of the conventional uses of EF figures (see Wa-
ckernagel et al. 1999, 2005). By assuming that the ‘fair’ lifestyle consists of the one
allowing the reproduction of natural resources, those interpretations rely implicitly on a
resource-centred sustainability standard that has no obvious ethical support.
Nevertheless, although it casts some doubts on the relevancy of usual interpretations of
EF figures for intergenerational justice, that criticism does not question the validity of
other possible interpretations, which might be immunized against it. Actually, whereas
usual interpretations of EF figures are based on the resource-centred sustainability stan-
dard—whose significance is questionable—the reliance on that standard is not the unique
possible one.
To see the possibility of relying on other ethical standards of intergenerational justice, it
is crucial to notice that the EF indicator, although it aggregates goods by means of their
costs in terms of natural resources, can nonetheless, under some conditions, allow the
making of judgements about intergenerational justice in welfare terms. Hence, under some
conditions, the EF can be compatible with other—non-necessarily physical—ethical
standards of intergenerational justice. Let us now be more precise about what those
conditions are.
Clearly, EF measures do not, in their usual form, allow us to study intergenerational
justice in welfare terms, because EF measures depend on the general consumption level in
the society and on the effectiveness of the production technology in terms of natural
resources. Hence, the fact that a society exhibits a higher EF than another can be caused
either by a higher consumption in that society—so that its members are better off—or,
on the contrary, by a more wasteful production technology—so that its members are not
better off.5
Thus, if one wants to draw, on the basis of EF inter-temporal inequalities, some con-
clusions about the welfare of different generations, it is necessary to compute EF measures
under the assumption of a fixed technology of reference, that is, ‘net’ EF measures, as
suggested by Haberl et al. (2001). Net EF figures, by measuring the hypothetical pressure
put on nature by a society under a technology of reference, allow us to abstract from
5 That fact is acknowledged by Wackernagel and Yount (2000), when they argue that a reduction offootprint does not necessarily reduce human welfare.
680 G. Ponthiere
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differences in production technologies, and to interpret inter-temporal inequalities in EF in
welfare terms.
To see this, let us suppose that economic welfare is additive over time, and increasing
and concave in consumption. Moreover, let us abstract from intra-period inequalities.
Under those assumptions, it is straightforward to see that, in an overlapping generations
one-good economy with stationary population size and age-structure, inequalities in net EF
figures are equivalent to inequalities in generational welfare. Actually, once the technology
is fixed, the EF becomes a consumption index, so that it is possible, under some
assumptions on welfare, to ‘jump’ from inequalities in net EF to inequalities in lifetime
welfare. Generations alive at periods where the net EF is higher must be characterized by
higher lifetime welfare levels.
Naturally, the interpretation of net EF measures as indexes of generational lifetime
(economic) welfare is heterodox, and requires some—non-weak—assumptions on welfare.
However, that interpretation has the virtue to cast a new light on existing interpretational
tensions raised by EF measures. Actually, the interpretation of conventional, ‘raw’ EF
figures is often made difficult by the fact that raw EF figures measure something that is
neither to be maximized (because societies with the highest EF are far from ‘models’), nor
to be minimized (because societies with the lowest EF are often the ones with the lowest
standards of living).
The heterodox interpretation of EF figures proposed here makes that confusion disap-
pear. Once net EF figures are computed and interpreted as indexes of generational
economic lifetime welfare, it appears that the reason why EF figures measure something
that is neither to be maximized, nor to be minimized, is that the EF indicator is not
concerned with the natural environment per se (unlike what usual interpretations suggest),
but with environmental justice between people. Hence, what has to be interpreted is not a
single EF figure, but, rather, the entire distribution of EF figures across time and space.
Furthermore, besides its virtue to make interpretational tensions vanish, the heterodox
interpretation of net EF measures as indexes of generational lifetime welfare makes also
appear that EF figures can be interpreted in various ways, and do not necessarily require
the use of a physical ethical standard, such as resources-centred sustainability. Once net EF
inequalities can be interpreted as welfare inequalities between generations, the fairness of
the actual use of nature can also be assessed in the light of other, welfare-based, ethical
standards.
More precisely, one can, under several assumptions about technology and about the
laws of reproduction of nature, compare the actual (net and raw) EF profiles with the fair
EF profiles recommended by distinct, welfare-based ethical standards. Such standards
could be, for instance, egalitarian welfarism, requiring the maximization of the welfare of
the worse-off generation, or, classical utilitarianism, defining the fair use of natural
resources as the one maximizing the total welfare of all existing generations.6 Egalitarian
welfarism would, under a fixed rate of regeneration of natural resources and a constant-
return-to-scale technology with a constant technological progress, imply a constant net EF
profile, and a decreasing raw EF profile (allowing early generations to deplete nature to a
larger extent, to compensate their worse technology). On the contrary, classical utilitari-
anism would, under such conditions, recommend increasing net and raw EF profiles. If the
future technology is more efficient than the current one, the depletion of natural resources
should be postponed to future generations, who will make a better use of these. A strong
6 Note that the solvability of the fair EF profile under classical utilitarianism requires, under no discounting,a finite number of generations.
The ecological footprint: an exhibit at an intergenerational trial? 681
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tendency of nature to reproduce itself supports also the postponement of the use of natural
resources, to let these accumulate themselves.7
One may question the validity of such descriptive analyses of environmental justice
between generations, on the grounds of the limited validity of the assumptions made on
technological progress and nature’s regeneration (see Sections ‘The ecological footprint
and the knowledge of nature’s regeneration’ and ‘The ecological footprint and the
knowledge of technological progress’). But those criticisms are different from the argu-
ment suggesting that the EF, being a physical indicator—and thus requiring a physical
interpretation—cannot help for the study of intergenerational justice.
Hence, the questioning, on the grounds of the purely physical nature of the EF, of the
status of the EF indicator as an exhibit at an intergenerational trial is not fully convincing.
Provided additional assumptions are made, it is possible to use EF measures to judge the
intergenerational fairness of the current use of natural resources without necessarily relying
on the usual—somewhat narrow—resources-centred sustainability standard.
3 The ecological footprint and the aggregation criticism
Another criticism consists of questioning the extra-value brought by the EF indicator in the
study of intergenerational justice on the grounds of its highly aggregated nature, which,
although pedagogically useful, may nonetheless be inadequate for the purpose at hand.
That criticism, which was made by, among others, van den Berg and Verbruggen
(1999), Ayres (2000), Opschoor (2000) and van Kooten and Bulte (2000), goes as follows.
EF figures, by measuring the total pressure put on nature at a particular point in time,
provide only a global view of the extent to which natural resources are used by current
generations. Although that global view, by summarizing a complex situation into a single
figure, has the virtue to make current generations aware of the actual depletion of nature, it
has also a non-negligible informational cost. EF statistics tends, by aggregating the pres-
sures put by current generations on different aspects of nature, to ‘hide’ the diverse pieces
of information on which it is based. Such pieces of information may be most relevant for
intergenerational justice, so that the computation of EF figures involves inevitably an
undesirable loss of information.
To illustrate this, let us consider the example of an economy with two natural resources
A and B, which are used in the production of various consumption goods. Those resources
differ by the rate at which these reproduce themselves over time, resource A reproducing
itself at a constant rate lower than the one at which resource B reproduces itself. Let us now
compute EF figures, by firstly converting the quantities of resources A and B required by
the production of consumed goods into surface, and, then, by aggregating these. It is not
difficult to see that a given EF figure may correspond to very different situations,
depending on the extent to which resources A and B are depleted. If the measured total
pressure put on nature is due to a large depletion of resource A, and to a low depletion of
resource B, this may have, given the lower regeneration rate of resource A, worse con-
sequences on future generations.8 However, the EF, by being highly aggregated, does not
7 Note that the extent to which postponing the use of resources is socially desirable depends on theconcavity of temporal welfare: the more concave welfare is in consumption, the lower the gains from savingresources are.8 The extent to which this is so depends on the degree of substitutability in the production process (seeinfra).
682 G. Ponthiere
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discriminate between those situations, which differ significantly as far as environmental
justice between generations is concerned.
Thus, the highly aggregated nature of the EF should be regarded as both a strength and a
weakness of that indicator. On the one hand, it is true, as Wackernagel and Rees (1997)
argued, that the EF promotes the collective awareness of the global pressure put by current
generations on nature. As Costanza (2000) underlined, it is the mono-dimensionality of EF
measures that helps people visualizing the size of Man’s impact on nature. However, on the
other hand, the EF indicator does not tell us how each natural resource—taken sepa-rately—is used. Given that natural resources follow various reproduction laws, and are
subject to various depletion patterns, the EF may show us only one part of reality: the tip of
the iceberg.
Hence, the EF indicator, by aggregating—and thus hiding—pieces of information that
are relevant for intergenerational justice, does not exhaust the list of exhibits required for
an intergenerational trial. The EF cannot dispense us from studying the depletion of natural
resources individually, which matters also for environmental justice between generations.
Nevertheless, although the criticism of EF figures on the grounds of their highly
aggregated nature is well-founded, one could hardly use that criticism to question the
overall significance of EF calculations for the assessment of the fairness of the current use
of nature. Contrary to the conclusions drawn by Opschoor (2000), the aggregation criticism
does not question footprint analyses in general, but, rather, emphasizes the necessity to
complement global footprint assessments by the calculation of disaggregated footprint
measures. A synthetic indicator providing a global picture of the pressure put on the natural
environment remains useful. The aggregation criticism implies only that aggregated EF
measures should be complemented by more disaggregated footprint measures.9
4 The ecological footprint and the different number problem
The conventional use of EF measures in an intergenerational context can also be criticized
on the grounds that it mistakenly regards the number of future people as independent from
current actions. However, as Kavka (1978) emphasized, our current actions—including our
depletion of natural resources—will influence the number of future people. The situation
faced corresponds to what Parfit (1984) called a different number problem. Thus, EF-based
judgements postulating a fixed number of generations (or people) seem to be irrelevant: if
the number of future people depends on current decisions, why should current generations
worry about the natural resources available for—contingent—future generations?
Actually, even if the current EF is higher than the postulated ethical standard—e.g. bio-
capacity—one can argue that such an excessive use is not unfair with respect to future
people. The reason why this is not unfair is that future people will exist only if enough
natural resources are still available at that time. Hence, if the number of people tends to
adjust itself to our actions, it seems that we can deplete nature today without any con-
straint. Thus, while Ferguson (1999, p. 153) argued, on the basis of EF figures, that, in
order to live in a sustainable way, western European countries and the U.S. should reduce
significantly their populations, one may reply to this that there is no point living in a
sustainable way, because future people will not suffer from non-existing. It follows from
this that EF figures seem to be irrelevant for the issue of intergenerational justice. But is
that criticism really convincing?
9 For footprint analyses at various aggregated and disaggregated levels, see Wiedmann et al. (2006).
The ecological footprint: an exhibit at an intergenerational trial? 683
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True, the number of future people may depend on our current actions, and, thus, on the
precise extent to which we are depleting natural resources. But even if one adheres to that
statement, this does not suffice to make EF measures of the pressure put on nature irrel-
evant. The observation that the number of future people will depend on the current
depletion of nature implies that the number of future generations to be used in the deri-
vation of a fair EF profile under a particular ethical standard should be modelled as a
function of the EF itself. However, that corollary does not suffice to make the calculation
of EF measures useless.
To illustrate this, let us suppose that, in the current state of the world, we are facing a
choice between two ‘lifestyles’, imposing two distinct pressures on nature, and leading, infine, to two different (raw and net) EF levels, EFlow and EFhigh. Let us assume that, under
the low pressure on nature (i.e. EFlow), the number of future generations is high, and equal
to, let us say, 100,000 generations. However, under the high pressure on nature (i.e.
EFhigh), only 85,000 generations will exist. Does the dependency of the number of future
generations on the current EF level affect the significance of the EF for the study of
intergenerational justice?
The fairness of each ‘lifestyle’—whatever the population size is the same in each case
or not—can only be assessed by first computing net EF profiles over existing generations
under each scenario, and, then, by discussing the precise extent to which those profiles
depart from the fair EF profile under the chosen standard of intergenerational justice. Only
such an analysis can tell us which lifestyle is the most fair with respect to future gener-
ations. Hence, judging the fairness of each current lifestyle with respect to future
generations—whatever their number is—could hardly be made without comparing actual
EF profiles with the EF profile recommended by the selected ethical standard.
One should thus distinguish two stages in the making of an intergenerational trial: (1)
the selection of an ethical standard dealing with situations where the number of generations
is not fixed; (2) the use of EF figures as an empirical tool on the basis of which one can
evaluate the fairness of different scenarios in the light of the selected ethical standard.
There is no doubt that selecting an ethical standard of intergenerational justice when the
number of generations varies is a complex task, as shown by the population ethics liter-
ature.10 However, that difficult choice does not affect the relevancy of EF measures for the
comparison of the actual use of natural resources with the use recommended by the
(selected) ethical standard.
5 The ecological footprint and the uncertainty about future generations’ existence
Whereas the fact that current actions may influence the number of future people does not
disqualify EF measures, the relevancy of the EF for the study of intergenerational justice
may nonetheless be questioned on the grounds that the interpretation of EF measures relies
on strong assumptions on the mere existence of future people. Actually, although EF-based
analyses presuppose that some people will necessarily exist in the future, it might be the
case, as Dasgupta and Heal (1979) rightly emphasized, that future people will not exist at
all, because of an event having nothing to do with our actions (e.g. a meteor falling on the
Earth).
10 The complexity of the task is well illustrated by the recent treatise of Blackorby et al. (2005). The largestdifficulty consists of selecting what Broome (2004) calls a ‘welfare level neutral for existence’ (i.e. makingthe existence of a person neutral from a social point of view).
684 G. Ponthiere
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In other words, one may question the relevancy, for intergenerational justice, of com-
paring actual EF figures, reflecting the current depletion of natural resources, with fair EF
levels recommended by particular ethical standards (whatever these are), on the grounds
that future people may simply not exist. Hence, investigating whether the current pressure
put on nature is fair or not—while taking the existence of some future people as given—is
irrelevant.
That criticism, based on the possible non-existence of future people (see Dasgupta and
Heal 1979), differs from the one discussed in the previous Section. The latter questioned
the significance of EF figures on the grounds that the number of future people will adapt to
our actions, so that we should not care about future people when depleting nature today. On
the contrary, the present criticism questions the relevancy of EF measures on the grounds
that the number of future people is not under our control, and is unknown. Hence, state-
ments on the fairness of the current depletion with respect to future people, by taking the
existence of those people as given—while it is not—are highly speculative and not far from
worthless.
Why should one worry about the natural resources available for future people, if the
existence of those temporally distant people is highly uncertain? Once we acknowledge
that future people may not exist, our duties towards them are no longer obvious, and the
value of judgements drawn from comparing EF figures with fair EF levels becomes
questionable.
However, it should be stressed here that acknowledging the uncertainty about the
number of future people questions the validity of some EF-based judgements, but not of all
of them. Whereas the uncertainty about the number of future people makes EF-based
judgements questionable if these rely on the postulate that future people will live for sure,
the uncertainty about the number of future generations on the Earth casts no doubt on the
validity of EF-based judgements taking the possibility of an exogenous extinction of
Mankind into account.
Actually, it is possible, when computing the fair EF level under a particular ethical
standard, to assume that there exists a strictly positive exogenous risk of extinction of
Humanity at all points in time, and to derive the fair EF profile accordingly. Then, in a
second stage, that fair EF profile could still be compared with the actual one, and judge-
ments could be drawn concerning the fairness of the current use of natural resources with
respect to possible—but not certain—future generations. Hence, the existence of a positive
probability of extinction of life on the Earth does not disqualify the use of EF measures as a
basis for the making of an intergenerational trial. On the contrary, it requires a modification
of the definition of the fair EF taken as a reference, in order to incorporate the risk of
extinction.
The possibility that life might cease to exist on the Earth at some point in the future is
thus not sufficient to question the use, in principle, of EF indicators. However, the
uncertainty about the length of Mankind raises two complex problems for the assessment
of the fairness of the depletion of natural resources, the first being theoretical, while the
second is practical.
The first problem consists of determining the precise form under which the uncertainty
about the existence of future generations should be incorporated into the ethical standard
used as a reference for the definition of a fair use of natural resources. That question can be
reformulated as the search for a set of axioms of choice under uncertainty, which would not
conflict with basic intuitions about intergenerational justice. A first problem is whether one
can reduce the situation of uncertainty about the length of existence of Humanity into a
situation of risk about the length of existence of Humanity (in which probabilities of
The ecological footprint: an exhibit at an intergenerational trial? 685
123
Humanities of different lengths can be estimated). But even if that reduction can be made,
the selection of a framework modelling the risk about the length of Mankind is not trivial.
As illustrated by the debates raised by uncertainty-based ‘pure’ discounting under classical
utilitarianism, introducing risk in conventional ethical standards is far from
straightforward.11
The second problem raised by the uncertainty about future generations’ existence
concerns the calibration of the exogenous risk of extinction. Indeed, even if one can select
a plausible ethical standard taking uncertainty about the length of Humanity into account,
the making of judgements about the fairness of the current use of natural resources requires
to assign a particular value—or, at least, some interval of values—to the probability that
life on the Earth will cease. Otherwise, if it is not possible to calibrate that risk, the fair EF
level cannot be computed, so that actual EF figures cannot be contrasted with fair EF
levels, and no judgement can be made as far as the fairness of the current use of nature is
concerned.
Those two difficulties raised by the uncertainty about future people’s existence could be
overcome by arguing that, even if future people may not exist, current generations should
behave as if the existence of future generations was certain, even if it is not the case. Hence, if
one follows that ‘as if’ requirement, judgements on the fairness of the current depletion of
nature can still be made by comparing actual EF levels with fair EF levels under particular
ethical standards taking the existence of some number of future generations as given.
Naturally, one may regard that ‘as if’ requirement as an ad hoc solution allowing us to
escape from all theoretical and practical difficulties raised by uncertainty about future
people’s existence. Actually, it is hard to see why the lower likelihood of existence of very
distant future generations should not be taken into account when defining a fair EF level,
and when assessing the fairness of the current depletion of natural resources.
However, whatever one adheres to the ‘as if’ requirement or not, acknowledging the
uncertainty about future people’s existence does not question the significance of EF measures
for the assessment of the fairness of our actions with respect to future generations. Uncertainty
about future people’s existence can be incorporated into the ethical standard from which the
fair EF level is derived. Whatever the way by which that incorporation is made, one will
always have, in fine, to compare that resulting fair EF level with the actual, observed one.
Hence, uncertainty about the number of future people does not question the role played by EF
figures when discussing the fairness of the current use of natural resources.
6 The ecological footprint and the non-identity problem
Beyond the facts that current actions may influence the number of future people, and that
the existence of future people may also depend on uncontrollable events, there can be no
doubt that the lifestyle prevailing today is also likely to affect what future people will be.
Hence, we face here what Parfit (1984) named a non-identity problem. Actually, selecting a
specific lifestyle today—leading to a particular pressure put on nature, measured by the
EF—is likely to influence the identities of future people, and their preferences. The reason
why this is the case is that the identities and preferences of future people are not given to
them, but are learned by future individuals, as this was stressed by, among others,
Boulding (1969).
11 The seminal work on discounting on the grounds of the more uncertain existence of future people isDasgupta and Heal (1979). See also Bommier and Zuber (2006) for recent advances on that issue.
686 G. Ponthiere
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However, acknowledging this dependency of future people’s identities and tastes on our
current actions is not without consequences on the possibility of an intergenerational trial,
especially if one would like that trial to be based on a welfarist ethical standard (Section
‘The ecological footprint and resources-centred sustainability’). Once the tastes of future
people depend on what we do, it becomes hard to assess the fairness of current actions.
Judging the fairness of current actions is especially difficult when individual tastes are
subject to an adaptation process of the kind studied in Elster (1983), where the availability
of resources tends to shape people’s preferences.
To see this, let us turn back to Fig. 1, according to which we are currently over-
exploiting natural resources, in such a way that is not compatible with the regeneration of
nature. Is such an excessive use of natural resources unfair with respect to future gener-
ations? If one adheres to resources-centred sustainability standard, and if one takes the
number of future people as certain and given, the answer is definitely yes. However, if one
relies on a welfarist ethical standard, one may argue, on the contrary, that such a depletion
is not unfair, on the grounds that future generations’ preferences will be ‘adapted’ to the
scarcity of natural resources prevailing at the time of their existence. Hence, the low
remaining stock of natural resources will not affect the welfare of those future people with
tastes different from ours.
But if people’s preferences tend to adapt to the available resources, does any com-
parison of the actual EF with the fair EF under fixed preferences make any sense? After all,
if over-depleting resources today is not unfair (because future people, by adapting their
tastes, will not suffer from our use of resources), judgements based on EF measures seem
to become hardly informative as far as intergenerational justice is concerned.
However, contrary to that severe conclusion, it is not obvious that the endogeneity of
tastes highlighted by Boulding (1969) and Elster (1983) casts some doubts on the relevancy
of the EF indicator for the study of intergenerational justice. Actually, the endogeneity of
tastes does not question the use of EF measures in general, but only the comparisons of
actual EF levels with fair EF levels defined under a welfarist ethical standard. Hence, the
endogeneity of tastes casts some doubts on the reliance on a welfarist standard, but not on
the general use of EF measures. The existence of psychological mechanisms adapting
tastes to the prevailing circumstances does not question the meaningfulness of comparing
EF with bio-capacity.
Moreover, one should also notice that individual preferences will not necessarily adapt
in the direction of accepting the prevailing scarcity of natural resources. It might be the
case that the preferences of future people differ from ours by valuing more—instead of
less—natural resources, as a reaction to their stronger scarcity. Hence, although future
people will not have the same preferences as ours—so that welfare comparisons relying on
fixed, common preferences constitute approximations—it is nonetheless hard to know how
tastes will evolve. The shift in preferences will not necessarily go in the direction of
preferring goods whose production requires the use of fewer—rather than more—natural
resources. Thus, taking preferences as fixed over time may lead to underestimate—rather
than overestimate—the unfairness of our depletion of nature with respect to future
generations.12
12 Another limitation of the adaptive tastes criticism arises from the fact that the amount of naturalresources consumed by humans depends not only on their tastes, but, also, on how the society is organized(which is something on which individuals have, in the short run, little control). Hence, EF-based analysesremain relevant, as the adaptation of future generations’ tastes cannot avoid a large welfare loss due tolimited natural resources.
The ecological footprint: an exhibit at an intergenerational trial? 687
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All this suggests that acknowledging the non-constancy of preferences does not suffice
to disqualify EF measures as a basis allowing empirically grounded judgements about the
fairness of the depletion of nature. On the contrary, the non-constancy of preferences
requires, when computing the fair EF level, to make not one, but several postulates on the
evolution of people’s preferences. A recent example of EF studies including such a multi-
scenario analysis for the evolution of tastes is provided by Senbel et al. (2003).13 In their
forecasting of EF for North America over 2000–2100, Senbel et al. used three scenarios:
‘simplicity’, ‘moderation’ and ‘luxury’, each of these involving different tastes and con-
sumption sets.
To conclude, the non-identity problem does not question the use of EF measures as a
basis for making judgements about the fairness, with respect to future generations, of the
current depletion of nature. That problem requires only, when making such judgements, a
particular attention to be paid to the issue of the evolution of preferences over time, and,
also, to the question of which preferences shifts should be regarded as morally relevant.
That latter point raises the well-known—but complex—problem of the optimal degree of
paternalism in normative economics.14 But those problems do not concern the EF in
particular, and can be discussed without questioning the role of the EF in the study of
intergenerational justice.
7 The ecological footprint and the knowledge of nature’s regeneration
When defining the fair EF level to be compared, in an intergenerational trial, with actual
EF figures, a central requirement, besides the choice of an ethical standard, is to make
plausible assumptions on the laws of reproduction of nature. Actually, the extent to which
the current depletion of resources is fair depends on its impact on the quantity of natural
resources available for future generations, which is determined by how nature reproduces
itself.
If, for instance, one assesses the fairness of current depletion by comparing the actual
EF with bio-capacity (see Section ‘Introduction’), the resulting judgement depends sig-
nificantly on how bio-capacity is computed. As this is discussed in Wackernagel et al.
(2005), the computation of bio-capacity requires the making of various assumptions on the
reproduction of natural resources. Alternatively, if one compares the actual EF with the fair
EF under a classical utilitarian standard, the same sensitivity to the laws of reproduction of
nature arises. Under a constant rate of regeneration of resources, a higher reproduction of
nature—taken here as a single input—leads to a more increasing fair net EF profile: a
higher ‘rate of return’ on natural ‘capital’ makes the saving of those resources more
desirable from a utilitarian perspective.
However, the dependency of the fair EF profile on the postulated laws of reproduction
of nature is not unproblematic for the making of an intergenerational trial. Actually, as this
was stressed by Ayres (2000), Deutsch et al. (2000) and Rapport (2000), the laws under
which natural resources reproduce themselves are not only diverse, but, also, highly
complex and largely unknown.15 Hence, drawing, on the basis of EF figures, conclusions
about the fairness of the current depletion of nature seems, given the lack of knowledge on
13 See also van Vuuren and Bouwman (2005).14 On paternalism, see Broome (1994).15 On the various laws of reproduction of natural resources, see Clark (1990).
688 G. Ponthiere
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the concrete effects of our actions on the future stock of all those resources, highly
speculative and questionable.
That criticism is quite convincing, as it is obvious that our knowledge of the laws of
reproduction of nature is limited: there exist millions of distinct species and resources,
whose reproductions follow various laws, many of these being still unknown. Hence, any
statement on the fairness of current depletion—which has to be based on some assumptions
on the reproduction of nature—is necessarily fragile. All this tends thus to cast some
doubts on the comparison, carried out in Section ‘Introduction’, of the EF with bio-
capacity, on the grounds that the latter can only be a proxy of the EF allowing the exact
reproduction of nature as a whole. Similarly, our lack of knowledge on how nature
reproduces itself tends also to question the exactness of all EF-based judgements relying on
approximate assumptions for those laws.16
Nevertheless, one can hardly deduce from that criticism that EF measures are irrelevant
for the study of intergenerational justice. Actually, our lack of knowledge on the laws of
regeneration of natural resources does not suffice to disqualify EF measures. The reason for
this is that, even if we do not know the exact consequences of the current depletion of
natural resources on the quantity of those resources available for future generations, this
dispenses us neither from measuring the actual depletion of nature, nor from analysing the
extent to which that depletion is, in the light of the knowledge we have, fair with respect to
future generations.
Our lack of knowledge on nature’s reproduction can hardly be regarded as a good
reason for ignoring the consequences of our actions on future people, so that it makes
sense, even under an imperfect knowledge, to compute EF figures, and to contrast these
with what seems to be a fair EF level under plausible assumptions on nature’s laws. For
that purpose, one should rely not on a single, but on several plausible scenarios for the
reproduction of nature.
Hence, whereas our imperfect knowledge of nature’s reproduction makes the fair EF
level more difficult to define and compute, this does not, however, question the principle of
making an intergenerational trial through the comparison of actual depletion of natural
resources—as synthesized by EF figures—and a fair depletion of resources, even if this has
to be approximated by means of several sets of hypotheses on nature’s regeneration.
8 The ecological footprint and the knowledge of technological progress
Judgements about the fairness of the depletion of nature must rely also on some postulates
on the production technology, and on its evolution over time. As stressed by Roemer
(2005), postulates on technology—especially the assumed substitutability between
inputs—play a crucial role in the definition of a fair depletion of natural resources.
Actually, a sufficiently large substitutability between human-made capital and natural
capital can strongly weaken the constraints imposed by a given standard of intergenera-
tional justice.
Even if one abstracts from substitutability issues, and supposes that production involves
a natural resource (let us say ‘surface’) as a unique input, the extent to which current
actions will affect future generations depends on how efficient the technique used by future
16 Note that bio-capacity depends not only on natural laws, but, also, on human intervention into ecosys-tems, and, thus, on technologies. Their evolution in the future is, as discussed in Section ‘The ecologicalfootprint and the knowledge of technological progress’, also difficult to forecast.
The ecological footprint: an exhibit at an intergenerational trial? 689
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generations will be. For instance, under egalitarian welfarism, the higher technological
progress is, the more decreasing the fair raw EF profile is across generations. Actually, if
future people benefit from a more efficient technology (requiring a smaller quantity of
natural resources for the production of each unit of good), early generations should be
allowed to extract more resources, to ‘compensate’ these for having a less efficient
technique.
Given that judgements comparing actual EF profiles with fair EF profiles are generally
dependent on some postulates about the evolution of technology over time, it is tempting to
criticize those judgements on the grounds of the necessary approximate nature of postu-
lates on the evolution of technology. Indeed, if one cannot know precisely what production
technologies will prevail in one or two centuries, how could one know the consequences of
the current use of nature on the capacity of future generations to satisfy their needs?
That criticism was formulated against EF calculations by, among others, Costanza
(2000), Ayres (2000), and Moffat (2000), who criticized existing EF applications on the
grounds of their (general) reliance on a fixed technology postulate. It is not difficult to see
how the existence of technological progress can be used to question the validity of
EF-based judgements emphasizing the unfairness of the current depletion of nature. If
future people can produce things with much smaller quantities of natural resources than
today, current over-depletion is not a serious problem, and, thus, the actual depletion of
resources is not unfair.
However, the mere existence of technological progress does not suffice to question
EF-based judgements about the fairness of the current depletion of nature, because
assumptions on how technology evolves over time can be incorporated into such judge-
ments. Thus, if technology consists of a problem for EF-based discussions on
intergenerational justice, this must come from the inadequacy of the assumptions made,
that is, from some kind of impossibility to forecast the evolution of production technology
over long periods of time.
There can be no doubt that the forecast of the evolution of technology is a complex task.
One may think, like North (1981), that technological revolutions are the output of the
existing institutions (e.g. property rights, market structures, political systems). Institutions,
by providing incentives to act in one direction or in another, influence the entire course of
history, including production techniques. However, while the picture provided by North is
plausible, it has a quite undesirable corollary: if institutional frameworks evolve in a
discontinuous manner, incentives to innovate—and, in fine, innovations—tend also to
evolve in a discontinuous manner, so that, given the existence of structural breaks, usual
forecast methods based on mere extrapolations can say only few things about the long-run.
It follows from all this that EF-based statements about the fairness of the current
depletion of nature conditionally on some expectations about technological progress are
highly speculative, because we are unable to predict which exact quantities of natural
resources will be required by the production of goods and services consumed in the future.
Nevertheless, the difficulties raised by the forecast of production techniques over long
temporal horizons could hardly question the use of EF measures as a basis for judging the
fairness of the current depletion of nature with respect to future generations. Actually,
those difficulties invite more complete judgements about the fairness of the current use of
nature, taking into account not one, but several distinct scenarios about the evolution of
technology.17 For instance, Senbel et al. (2003), relied, in their EF forecasts for North-
America over 2000–2100, on four technological scenarios—‘intensified production’,
17 Examples of such analyses are provided by Ferng (2002) and Senbel et al. (2003).
690 G. Ponthiere
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‘business-as-usual’, ‘conservation’ and ‘depletion’—and showed the sensitivity of future
EF to those scenarios.
Such a multi-scenario analysis could also be used to discuss the fairness of the current
depletion of natural resources. Thus, as it was the case with our imperfect knowledge of the
laws governing the regeneration of nature, our imperfect knowledge of the laws of the
material reproduction of a society by itself cannot constitute a sufficient motive to reject
any attempt to discuss, in the light of EF measures, how (un)fair the current depletion of
nature is.
9 Concluding remarks
This paper aimed at examining the extent to which EF measures constitute an empirical
basis—an exhibit—allowing an intergenerational trial on the depletion of natural resour-
ces. For that purpose, we reviewed major criticisms questioning the relevancy of EF
measures for the study of intergenerational justice. What can be concluded from the
present review?
The previous sections emphasized the various limitations of conventional EF-based
studies, which consist of comparing EF measures with bio-capacity estimates (see Wa-
ckernagel et al. 1999, 2005). The reasons why such comparisons can hardly inform us
about the fairness of the current depletion of nature are the following.
First of all, such applications rely on the—somewhat questionable—resources-centred
sustainability standard (Section ‘The ecological footprint and resources-centred sustain-
ability’). Moreover, the EF, being a synthetic indicator, tends to hide pieces of information
that may be most relevant for intergenerational justice (Section ‘The ecological footprint
and the aggregation criticism’). Conventional EF-based studies suffer also from the
dependency of the number of future people on current actions (Section ‘The ecological
footprint and the different number problem’), from the possible non-existence of future
generations (Section ‘The ecological footprint and the uncertainty about future genera-
tions’ existence’), and from the sensitivity of future people’s tastes to current decisions
(Section ‘The ecological footprint and the non-identity problem’). Finally, the interpre-
tation of EF measures in terms of intergenerational justice relies on fragile forecasts on
nature’s regeneration and technological progress (Sections ‘The ecological footprint and
the knowledge of nature’s regeneration’ and ‘The ecological footprint and the knowledge
of technological progress’).
Although those criticisms question conventional EF-based studies of intergenerational
justice, it should be stressed that various alternative uses of EF measures could, at least to
some extent, be immunized against those shortcomings. Hence, this paper suggests that
usual EF studies are quite imperfect ‘exhibits’, which should be complemented by alter-
native EF-based analyses of justice between generations. Recent studies have already
tackled some problems explored in this paper. For instance, Wiedmann et al. (2006)
produced footprint measures at various aggregation levels, while Ferng (2002) and Senbel
et al. (2003) dealt with the forecasting of future technology and lifestyles by means of
multi-scenario analyses.
Despite recent attempts to overcome some limitations of EF-based studies, the imper-
fect nature of the EF as an exhibit allowing an intergenerational trial raises the question of
the possible ‘domination’ of the EF by other indicators. Could other indicators of ‘strong’
sustainability, such as the biophysical pressure indicators discussed by Rennings
and Wiggering (1997), ‘dominate’ the EF? Alternatively, could ‘weak’ sustainability
The ecological footprint: an exhibit at an intergenerational trial? 691
123
indicators, such as Jackson and Stymne’s (1996) index of sustainable economic welfare
(ISEW), or the genuine progress indicator (GPI) (Cobb et al. 2001), avoid the criticisms
raised in this paper?
While a study of those rival indicators would require an entire paper on its own, it is not
difficult to see that those indicators suffer from several criticisms developed against the EF.
Indicators of strong sustainability, if less aggregated than the EF, avoid the aggregation
criticism, but their biophysical nature makes these hard to be interpreted in terms of
intergenerational justice. Weak sustainability indicators have also some weaknesses. True,
the ISEW and the GPI, which consist of correcting consumption for (among other things)
environmental damages, are monetary indicators, and, thus, avoid the problems raised by
the physical nature of the EF. However, in order to use such indicators in an intergener-
ational trial, assumptions must be made to ‘jump’ from the metrics of money to the metrics
of welfare.18 Moreover, the ISEW and the GPI are highly aggregated indicators that may
also hide important information. Furthermore, all those indicators are, like the EF, subject
to the problems of numbers and identities discussed in Sections ‘The ecological footprint
and the different number problem’, ‘The ecological footprint and the uncertainty about
future generations’ existence’, and ‘The ecological footprint and the non-identity problem’,
and could hardly avoid making—somewhat fragile—assumptions on nature’s regeneration
and future technology.
Hence, neither the EF nor those other indicators could be regarded as a ‘perfect exhibit’,
which could allow us to make a certain judgement on the fairness of the current use of
natural resources. All environmental indicators—monetary or biophysical, aggregated or
not—rely on specific informational bases and on particular assumptions, and, as such,
should be regarded as distinct—necessarily imperfect—exhibits complementing each
others.
The imperfection of those exhibits—including the EF—should not hide that, without
exhibit, there could be no trial at all, that is, there could be no explicit assessment of
arguments suggesting that our current actions are unfair with respect to future generations.
Therefore, despite its imperfections, the EF indicator has the virtue to open the possibility,
for humans, to become the own judges of their actions, and, hence, to be able to act, on the
basis of their judgements, in a more fair way with respect to future generations. All this
might well be only a promise, but a promise of justice may be the first step towards justice
itself. Hence, the—most demanding—task of measuring our depletion of nature is worth
being pursued.
Acknowledgments The author would like to thank Paul-Marie Boulanger, Alexander Cappelen, PaulCobben, Axel Gosseries, Russell Keat, Jonathan Seglow and Jurgen de Wispelaere for their helpfulcomments.
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