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*The views expressed in this brief are the authors’ and not those of the United Nations. Online publication
or dissemination does not imply endorsement by the United Nations.
Brief for GSDR 2015
Weak Sustainability versus Strong Sustainability
Jérôme Pelenc, Fund for Scientific Research (FRS-FNRS) and Free University of Brussels (ULB), Belgium
Jérôme Ballet, University of Bordeaux, GRETHA research unit, France
Tom Dedeurwaerdere, Fund for Scientific Research (FRS-FNRS) and Catholic University of Louvain
(UCL), Belgium*
The fundamental debate regarding
sustainable development is whether we
choose to adopt a strong or a weak
conception of sustainability. Weak
sustainability postulates the full
substitutability of natural capital whereas the
strong conception demonstrates that this
substitutability should be severely seriously
limited due to the existence of critical
elements that natural capital provides for
human existence and well-being. The
following science digest provides an overview
of scientific findings to support informed
debate among decision-makers regarding the
need to adopt a strong sustainability position
for the discussion and implementation of the
post-2015 sustainable development policies.
Introduction
Weak sustainability assumes that
natural capital and manufactured capital are
essentially substitutable and considers that
there are no essential differences between
the kinds of well-being they generate (Ekins et
al., 2003; Neumayer, 2003; Neumayer, 2012).
The only thing that matters is the total value
of the aggregate stock of capital, which should
be at least maintained or ideally increased for
the sake of future generations (Solow, 1993).
In such a perspective: “it does not matter
whether the current generation uses up non-
renewable resources or dumps CO
2
in the
atmosphere as long as enough machineries,
roads and ports are built in compensation”
(Neumayer, 2003, p1). Such a position leads to
maximising monetary compensations for
environmental degradations. In addition, from
a weak sustainability perspective,
technological progress is assumed to
continually generate technical solutions to the
environmental problems caused by the
increased production of goods and services
(Ekins et al., 2003).
Authors writing on strong
sustainability demonstrate that natural capital
cannot be viewed as a mere stock of
resources. Rather natural capital is a set of
complex systems consisting of evolving biotic
and abiotic elements that interact in ways that
determine the ecosystem’s capacity to
provide human society directly and/or
indirectly with a wide array of functions and
services (Noël and O’Connor, 1998; Ekins et al.,
2003; De Groot et al., 2003; Brand, 2009). The
proponents of strong sustainability invoke
several reasons to demonstrate the non-
substitutability of natural capital.
• Firstly, there is a qualitative difference
between manufactured capital and natural
capital. Manufactured capital is reproducible
and its destruction is rarely irreversible,
whereas the consumption of natural capital is
usually irreversible (for instance species
extinction is irreversible, whereas the
destruction of material goods or
infrastructures is not) (Ekins et al., 2003). In
addition, due to our lack of knowledge about
the functioning of natural systems we cannot
be sure of the effects on human well-being of
destroying natural capital (Dietz and
Neumayer, 2007). Acknowledging
irreversibility and uncertainties should lead us
to implementing a precautionary principle
regarding the use of natural capital.
• Secondly, since manufactured capital
requires natural capital for its production, it
can never be a complete substitute for the
biophysical structures of natural capital (Ekins
et al.). In addition, the contribution of natural
capital through the delivery of services to
human well-being is multidimensional. The
Millennium Ecosystem Assessment (2005)
captures these multiple linkages through the
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*The views expressed in this brief are the authors’ and not those of the United Nations. Online publication
or dissemination does not imply endorsement by the United Nations.
identification of four types of contributions
that ecosystem services make to human well-
being: security, basic materials for a good life,
health, and good social relations. Therefore,
ecosystem services provided by natural capital
play an important role in determining the
freedom of choice and action for human
beings (ibid.). In this view, natural capital is
instead seen as being complementary to
manufactured capital and other forms of
capital (human and social capital, etc.) in
producing human well-being (Brand, 2009)
and so manufactured capital cannot be a
complete substitute for it.
• Thirdly, an increase of future
consumption is not an appropriate substitute
for losses of natural capital (see among others
see Toman, 1992; Dedeurwaerdere, 2013).
The following exemple helps to grasp our
point: “Today’s generation cannot ask future
generations to breathe polluted air in
exchange for a greater capacity to produce
goods and services. That would restrict the
freedom of future generations to choose clean
air over more goods and services” (UNDP,
2011, p.17). This raises the key issue of
conserving natural capital for the sake of
future generation, i.e., intergenerational
justice issue.
Thus strong sustainability holds that
certain elements of natural capital are
« critical » due to their unique contribution to
human well-being (Ekins et al., 2003;
Dedeurwaerdere, 2013). These potentially
“critical” elements for human existence and
well-being can be conceptualised as
ecosystem services provided by natural capital
(Brand, 2009). This leads us to defining the
notion of critical natural capital. Critical
natural capital highlights the need to maintain
the ecological functioning of natural systems
above certain thresholds of degradation in
order to conserve the capacity of natural
capital to provide the services which are
critical for human existence and well-being
(Noël and O’Connor, 1998; Ekins et al., 2003;
Chiesura and de Groot, 2003, de Groot et al.,
2003; Dietz and Neumayer, 2007; Brand,
2009). Therefore critical natural capital
corresponds to the particular configuration of
natural capital that provides a particular set of
critical ecosystem services.
Nevertheless, strong sustainability
does not state that all ecosystem services
everywhere have to be sustained exactly as
they are. Some assessments must be made of
those services that play a particularly
important role in supporting life and
generating human well-being. And so, policies
for sustainability must be geared accordingly
(Ekins et al. 2003). However, strong
sustainability proponents recognize that the
uncertain state of knowledge about
ecosystems and ecosystem services, makes
very difficult to judge which services are
critical and which are not.
Scientific debate
Brand (2009) identifies six domains in
which natural capital and so ecosystem
services can potentially be critical: socio-
cultural, ecological, sustainability, ethical,
economic and human survival. This intrinsic
multidimensionality makes it very difficult to
assess the level of criticality and
substitutability of natural capital. Indeed,
acknowledging that natural capital and human
well-being are both complex and
multidimensional, implies having to deal with
multiple meanings, and with measurements
that are not necessarily either comparable or
commensurable (Scheidel, 2013). Moreover, it
has to be noted that in addition to the
“objective” ecological criteria (safe minimum
standards, minimum ecosystem size,
maximum sustainable yield, ecological
footprint, etc.), societal values and
perceptions, ethics and attitude to risk, also
play important roles in the determination of
what aspects of natural capital can be
considered “critical” (Ekins et al., 2003; De
Groot et al., 2003; Chiesura and De Groot,
2003; Brand, 2009; Dedeurwaerdere, 2013).
Hence, the definition of critical natural capital
relies not only on our capacity to provide
factual knowledge about socio-ecological
systems but also implies discussing the
normative values that underline our use of the
natural capital (Dedeurwaerdere, 2013).
Therefore, the definition of what constitutes
an intolerable loss, and so what is critical and
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*The views expressed in this brief are the authors’ and not those of the United Nations. Online publication
or dissemination does not imply endorsement by the United Nations.
for whom, requires both relevant factual
knowledge about the interactions between
natural capital and human well-being and a
normative basis to assess the sustainability of
these interactions. Consequently, there is a
need to move beyond the technical and
expert-based calculation of critical thresholds
of natural capital only (ibid.). As long as there
are multiple value involved in the definition of
critical natural capital and given the
irreducible uncertainties that characterise
complex socio-ecological systems, public
deliberation and stakeholders participation
(Van den Hove, 2000) seem to be required for
the definition of criticality of natural capital
(De Groot et al., 2003; Dedeurwaerdere,
2013).
In sum, implementing strong sustainability
requires a trans-disciplinary approach for
identifying and conserving critical natural
capital. The knowledge provided by natural
science constitutes crucial contributions for
identifying ecological thresholds and planetary
boundaries but they are not sufficient on their
own. Natural science research needs to be
combined with social sciences and their
interactions need to be embedded in a broad
societal debate about (i) levels of risk
acceptable to all populations (especially the
most vulnerable populations) and (ii) values
that underlie human development.
Issues for further consideration
• In terms of scientific methodology,
strong sustainability is to be greatly preferred
as the a priori position of full substitutability
of natural capital which appears improbable
for the aforementioned reasons.
• Improve multidimensional and
integrated assessment of the interactions
between the natural environment and human
well-being (e.g. improve the integrated
assessment of ecosystem services).
• Advance the construction of a
normative basis to assess the sustainability of
these interactions in a strong perspective.
Main differences between weak and strong
sustainability
Strong
sustainability
Weak
sustainability
Key idea The
substitutability of
natural capital by
other types of
capital is severely
limited
Natural capital and
other types of
capitals
(manufactured etc.)
are perfectly
substitutable
Consequences
Certain human
actions can entail
irreversible
consequences
Technological
innovation and
monetary
compensation for
environmental
degradation
Sustainability
issue
Conserving the
irreplaceable
« stocks » of
critical natural
capital for the
sake of future
generation
The total value of
the aggregate stock
of capital should be
at least maintained
or ideally increased
for future
generation
Key concept Critical natural
capital
Optimal allocation
of scarce resources
Definition of
thresholds
and
environmenta
l norms
Scientific
knowledge as
input for public
deliberation
(procedural
rationality)
Technic/scientific
approach for
determining
thresholds and
norms
(instrumental
rationality)
Source: Adapted from Mancebo, 2013
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*The views expressed in this brief are the authors’ and not those of the United Nations. Online publication
or dissemination does not imply endorsement by the United Nations.
References
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sustainable development. Ecological
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Chiesura, A., De Groot, R. (2003). Critical
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Dedeurwaerdere, T. (2014). Sustainability
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