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 :

• 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. ) does not change locally with respect to time:

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 () that depends periodically () on the independent variable time (Verhulst 1996):

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:

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 report, 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):

1. 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:

1. ¿How do we meet the needs of the present?
2. ¿How do we estimate the needs of the future?
3. ¿How do we reach consensus on how to address present and future needs?

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).