What does it mean to be sustainable?
The title question may seem trivial, particularly since the word is used ad nauseam in the press, academic literature, and political discourse. However, a closer examination shows that the concept of sustainability has been largely expanded from its initial definition, becoming ambiguous and even contradictory in itself.
An intellectually honest person recognizes that conceptual definitions are fundamental to establish meaningful operational definitions, which are particularly necessary in the technical fields. For the case of engineering, we are interested in defining a concept of sustainability that allows derivation of ideally well-posed problems, i.e. problems where a solution exists, it is unique and stable (Hadamard 1902). Otherwise, we are interested in deriving ill-posed problems that are at least numerically tractable (e.g. Tikhonov et al. 1995).
Sustainability
According to the Merrian-Webster dictionary, sustainability means “capable of being sustained”, i.e. “maintained at length without interruption or weakening” 1. From this definition we can derive some illustrations of the concept :
1 https://www.merriam-webster.com/dictionary/sustainable. Accessed on January 31, 2022.
- A sustained round of applause.
- A sustained chemical reaction inside a reactor.
- A sustained production of water from a water treatment plant.
Note that the above definition clearly establishes what we should understand by sustainable, and allows development of operational definitions for the concept.
For instance, we can mathematically approximate the above definition with the thermodynamic concept of steady state, which dictates that a given state variable in a system (e.g. \(\rho\)) does not change locally with respect to time:
\[ \frac{\partial \rho}{\partial t} = 0 \]
On the other hand, we can also approximate the above definition with the concept of periodic solution of a system, i.e. a given state variable (\(\rho\)) that depends periodically (\(T\)) on the independent variable time (Verhulst 1996):
\[ \rho(t+T) = \rho(t)\]
Note that the above definition establishes time as the primary variable to determine sustainability. However the definition does not impose how long a sustainable process should be maintained, nor the nature of the process itself.
Time scales of sustainable processes are linked to the nature of the process itself. For instance, a sustained round of applause can be achieved in a matter of seconds, whereas a sustained production of water can take hours to be achieved. In both cases, however, it is unreasonable to consider that such processes must be maintained indefinitely to be considered sustainable.
Such considerations are important, since modern definitions of sustainability address primarily technological processes that support human progress, and are thus particularly sensitive to innovation and disruption.
Sustainability redefined
Interestingly, Merrian-Webster additionally defines sustainability as “of, relating to, or being a method of harvesting or using a resource so that the resource is not depleted or permanently damaged.”
Similarly, the Encyclopaedia Britannica provides a more broad definition of sustainability (emphasis added) 2:
2 https://www.britannica.com/science/sustainability. Accessed on January 31, 2022.
sustainability, the long-term viability of a community, set of social institutions, or societal practice. In general, sustainability is understood as a form of intergenerational ethics in which the environmental and economic actions taken by present persons do not diminish the opportunities of future persons to enjoy similar levels of wealth, utility, or welfare.
The idea of sustainability rose to prominence with the modern environmental movement, which rebuked the unsustainable character of contemporary societies where patterns of resource use, growth, and consumption threatened the integrity of ecosystems and the well-being of future generations…
In both cases the definition of sustainability has been expanded to include preservation of the resources required to sustain a given process or system. In addition, the latter definition explicitly addresses complex systems such as social institutions or practices, and propagates the time scale to an unknown number of future generations. Such considerations introduce ambiguity to the concept, which in turn complicates efforts to bring forward operational definitions that properly map to the original set of propositions.
This conceptual ambiguity is often a deliberate attempt at drawing a moral relation between economical and political systems with respect to the underlying ecological system upon which they depend (Jenkins 2009). However, in other cases this ambiguity is the result of conflation between sustainability and sustainable development, and confusion when addressing specific operational frameworks in a given field (e.g. sustainable business).
Sustainable development
Most contemporary literature supports this broad definition of sustainability on the report of the World Commission on Environment and Development of the United Nations “Our Common Future” (WCED 1987), also known as the Brundtland repor, in honor to the Chair of the Commission and former Prime Minister of Norway, Gro Harlem Brundtland. This report defines sustainable development as follows (emphasis added):
- Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. It contains within it two key concepts:
the concept of ‘needs’, in particular the essential needs of the world’s poor, to which overriding priority should be given; and
the idea of limitations imposed by the state of technology and social organization on the environment’s ability to meet present and future needs.
The Brundtland report explicitly recognizes the importance of economic growth, particularly in poor countries, but establishes the need to conciliate such growth with environmental issues and social equity in order to achieve sustainable development. Notably, the report also recognizes that, along with the environment, technology and social systems are fundamental to drive human progress.
It is difficult -and certainly beyond the scope of this post- to estimate the profound impact that the Brundtland report had on shaping sustainability policies and initiatives over the last 35 years. It suffices to say that this report has allowed formulation of several operational frameworks of sustainable development, most notably the triple bottom line of sustainability (Elkington 1997), the Millennium Development Goals (UN 2000), and more recently the Sustainable Development Goals (UN 2015), also known as the 2030 Agenda for Sustainable Development.
Examining sustainable development
Lets focus our attention on the definition of sustainable development, to derive conclusions regarding the possibility of meaningful operational definitions. We can proceed by addressing the following questions:
- ¿How do we meet the needs of the present?
- ¿How do we estimate the needs of the future?
- ¿How do we reach consensus on how to address present and future needs?
Addressing present needs
If present needs refer primarily to necessities of the poor, then the problem of meeting such needs can be addressed by encouraging countries to adopt and maintain stable and effective political systems that support economic growth and technological innovation (see Tebaldi and Mohan 2010; Tebaldi and Elmslie 2008). An example of such political system would be a free-market economy supported by democratic institutions (Baumol 2002; Schumpeter 1976), however a general approach must consider measures to address the current needs of vulnerable population subjected to other systems of governance, including various forms of monarchies and dictatorships .
Since economic growth requires consumption of resources and energy, by necessity this growth will partially deplete resources that might be useful for future generations. In addition, pursuit of economic growth in developing nations may lead to initial economic inequalities and environmental degradation, therefore negatively impacting such dimensions.
It is worth to note that the previous effects are in contradiction with the propositions of sustainable development. Despite these contradictions, evidence has shown that at as economic growth progresses, economic inequality and environmental impacts tend to concurrently decrease (Kuznets 1984; Grossman and Krueger 1994).
In addition to economic growth, other nations may also place significant value to socio-cultural and religious traditions, and thus may consider an approach to sustainable development that prioritizes preservation of traditions. This observation highlights the multidimensional nature of defining needs for the present.
Considering the above, the problem of addressing the needs of the present is sufficiently well-posed; it can be properly defined for a state or a given geographical location, and afterwards reduced to feasible and meaningful metrics that allow assessment of proposed measures as a function of time. Therefore feasible solutions are likely to be found for this problem.
Estimating future needs
Future needs are by definition unknown, and therefore any approach to estimate them introduces significant uncertainties. A reasonable assumption is to consider that future generations will follow our current needs closely, and thus we simply project our current consumption of resources into the future in order to estimate the needs of future generations.
But the previous assumption produces a dead end, since it invariably reaches the a-priori conclusion that our development is unsustainable, and therefore we must drastically reduce our resource consumption to meet the need of future generations, even at the sake of disregarding the current needs of the poor. The previous assumption is also flawed, because it negates the emergence of technological innovations that offer radical new opportunities in terms of goods and services for future generations (Schumpeter 1976; Baumol 2002; Tupy and Pooley 2022).
Therefore we are left with significant uncertainty, which unfortunately turn the problem of estimating future needs into an ill-posed one, certainly unstable and likely intractable as long as the original proposition remains.
International consensus
The issue of international consensus in terms of sustainable development is no less challenging than the previous issues, since it is predicated upon them. Advancing a global agenda on sustainable development introduces opportunities for reconfiguration of relations between states (e.g. economic, cultural) and between states and non-state actors (e.g. corporations, non-governmental organizations). Such opportunities are likely to be capitalized by either state or non-state actors in order to advance their strategic interests, creating conditions for potential conflict with other states that may perceive disregard for their national interests.
Naturally one can expect that trade agreements, international law, intergovernmental organizations, and overall transparency will play a fundamental role in allowing the required flow of resources, the resolution of eventual conflicts, and the political agreements necessary for states to progressively achieve sustainable development while respecting their national sovereignty. Therefore, consideration of national interests, particularly national security, will play a significant role in securing consensus and promoting measures aimed at achieving goals for sustainable development.
Given its dependency on estimating need of future generations, the consensus problem is also ill-posed, and particularly intractable given the complexities of international relations.
An alternative approach
The previous analysis may seem gratuitous and unconstructive; after all we only had 35 years to highlight the shortcomings of the definition for sustainable development put forward by the Brundtland report.
This is however not the point of the previous analysis, as the focus is in observing that definitions matter, particularly when they support policies that will dramatically reduce much needed resources for the poor. Therefore definitions should be subject to careful examination, including correction to address shortcomings such as ambiguity, contradiction, and translation into ill-posed problems.
It seems appropriate at this point to put forward an alternative definition for sustainability, particularly one that is sufficiently well-posed. Here we turn our attention to the work of the economist and Nobel laureate Robert Solow, which offers the following definition for sustainable path (Solow 1993, 168):
A sustainable path for the economy is thus not necessarily one that conserves every single thing or any single thing. It is one that replaces whatever it takes from its inherited natural and produced endowment, its material and intellectual endowment. What matters is not the particular form that the replacement takes, but only its capacity to produce the things that posterity will enjoy. Those depletion and investment decisions are the proper focus.
According to Solow, in order for the concept of sustainability to be meaningful, “it must amount to an injuction to preserve productive capacity for the indefinite future”. Solow rightly recognizes that nothing can be produced without the use of natural resources, but emphasizes that resources are valuable not by themselves, but for their capacity to produce goods and services that are useful for both current and future generations. Therefore, in terms of sustainable ethics, each generation should produce assets of equal or greater value (reproducible capital) to compensate for the non-renewable resources it consumed to satisfy it needs.
In practice, the above definition translates to calculation of the value of depleted non-renewable resources that must be returned by assets of equal or greater value in order to sustain productive capacity. As such it is a sufficiently well-posed problem, one that we can actually hope to solve.
Indeed there is plenty of reason to believe that the above definition is appropriate for a sustainabile path; a cursory review of the state of affairs shows that valuable goods and services are not decreasing, but in fact increasing (Lomborg 2001; Tupy and Pooley 2022).
Conclusions
As seen in this post, a well-posed definition of sustainability refers to the capacity to maintain something without interruption or weakening in a given span of time. Similarly, a sustainable path also constitutes a well-posed definition, since it alludes at replacing depleted natural resources in terms of reproducible capital for posterity to enjoy.
On the other hand, sustainable development constitutes an ill-posed definition, since it requires estimation of uncertain future needs, which in the worst case translates into a contradiction of maintaining resources for future generations, while at the same attempting to produce economic growth for the current generation.
Without a proper conceptual definition it is not possible to define well-posed problems to address sustainability issues. As a result, proposed solutions are certainly likely not unique, unstable and incapable of addressing the original proposition.