Motivations

When we talk about sustainability, what are we talking about, really? I went looking for a systems-based definition of sustainability and I didn't find one that was clear and accessible to the general reader. The following is an attempt to provide such a definition.

Why is it important to have this kind of a definition of sustainability? If we are to reverse climate change while building a livable world for all of us, it will be important to exchange our unsustainable systems for sustainable ones. This work will depend on an understanding of what sustainability is.

Definition

A system that can persist over a defined time interval can be said to be sustainable over that interval.

As an example system, consider mountains. Mountains can persist from 10s of millions to billions of years. If a particular mountain is predicted to persist for another 50 million years, then it can be said to be sustainable over a 50 million year period.

Sustainability and climate

No system stands alone. Each system is part of one or more systems. The resource use of a system, when seen as part of a larger system, will be considered to be sustainable inasmuch as it contributes to the resource use of the larger system.

When you trace the relationships between systems in this way, you will always reach a global system. Each system is thus part of one or more global systems. It is the sustainability of global systems that should be given the highest importance in any sustainability analysis.

The resource use of a system, when seen as part of a global system, will be more or less sustainable inasmuch as it contributes to the resource use of the global system. It is these global effects which are most important when assessing the sustainability of a system.

A sustainability analysis should incorporate the ongoing resource use of the system under analysis. In addition it should incorporate the resources used to create the system, including any upstream resource use incurred by related systems in the process of creating the system.

Embedded or embodied emissions are resources that are consumed during the production and transportation of a product or activity. This includes everything from the extraction of raw materials to the manufacturing process and final delivery to the end customer.

Example 1: CO2e sustainability

Consider the sustainability of a single soccer ball, with respect to CO2e. A soccer ball is a relatively simple object and yet its supply chain is complex. The EPA provides this handy graphic description of the soccer ball's supply chain.

The lifecycle of a soccer ball includes resource extraction, manufacturing, transportation, usage, and disposal.

Raw materials involved include polyurethane/PVC and rubber, which are sourced in part from crude oil, and cotton. These raw materials are processed into plastics and fabrics.

In a factory, the ball is manufactured with machine cutting and stitching, as well as heat-based forming of plastic components. The ball is glued together. Designs are then printed onto the surface of the ball and it is coated with plastic.

A finished soccer ball may travel a very long distance to reach its eventual market or a consumer's home.

The ball will last more or less depending on its usage. At the end of its life the ball will be transported either to a recycling facility or to a landfill.

The following formula can be used to determine the CO2e emissions related to a soccer ball. $$\begin{align} embedded\_co2e_{ball} = \hspace{0.5em} & co2e_{extract\_oil} + co2e_{grow\_cotton} + co2e_{make\_plastics} \\ & + co2e_{make\_fabric} + co2e_{build\_factory} + co2e_{cutting\_stitching} \\ & + co2e_{forming\_plastic} + co2e_{printing} + co2e_{plastic\_coating} \\ & + co2e_{shipping} \\ co2e_{ball} = \hspace{0.5em} & embedded\_co2e_{ball} + co2e_{disposal\_transport} \\ \end{align} $$

If we consider the global context for this system, we can see that the soccer ball can be considered sustainable with respect to CO2e inasmuch as it minimizes the CO2e emmissions associated with its entire life cycle. The goal of a sustainability effort for a soccer ball should be to minimize the value of this formula.

Example 2: H2O sustainability

Similarly we can consider the water use for the life cycle of a soccer ball. $$ \begin{align} embedded\_h2o_{ball} = \hspace{0.5em} & h2o_{extract\_oil} + h2o_{grow\_cotton} + h2o_{make\_plastics} + h2o_{make\_fabric} \\ & + h2o_{build\_factory} + h2o_{cutting\_stitching} + h2o_{forming\_plastic} + h2o_{printing} \\ & + h2o_{plastic\_coating} + h2o_{shipping} \\ h2o_{ball} = \hspace{0.5em} & embedded\_h2o_{ball} + h2o_{disposal\_transport} \\ \end{align} $$

For this resource we might also consider different forms of water use, for example water use that depletes an aquifer (a) or impedes local agriculture. $$ \begin{align} embedded\_h2o_{a_{ball}} = \hspace{0.5em} & h2o_{a_{extract\_oil}} + h2o_{a_{grow\_cotton}} + h2o_{a_{make\_plastics}} + h2o_{a_{make\_fabric}} \\ & + h2o_{a_{build\_factory}} + h2o_{a_{cutting\_stitching}} + h2o_{a_{forming\_plastic}} + h2o_{a_{printing}} \\ & + h2o_{a_{plastic\_coating}} + h2o_{a_{shipping}} \\ h2o_{a_{ball}} = \hspace{0.5em} & embedded\_h2o_{a_{ball}} + h2o_{a_{disposal\_transport}} \\ \end{align} $$

Example 3: Overall sustainability

We can generalize these formulas to the case where there are an arbitrary number of resources under consideration.

$$ \begin{align} & \text{Let} \hspace{0.5em}p\hspace{0.5em} \text{be the primary product or activity. (In this case, the soccer ball.)} \\ & \text{Let} \hspace{0.5em}R\hspace{0.5em} \text{be the set of resources under analysis.} \\ & \text{Let} \hspace{0.5em}f(n)\hspace{0.5em} \text{be the function that normalizes resource values.} \\ & \text{Let} \hspace{0.5em}k_r\hspace{0.5em} \text{be the weight appiled to each resource r when compiling the sum.} \\ \\ \end{align} $$ $$ \begin{align} s\_p = \sum_{r \in R} [ & k_r * f(r_{extract\_oil}) + k_r * f(r_{grow\_cotton}) \\ & + k_r * f(r_{make\_plastics}) + k_r * f(r_{make\_fabric}) + k_r * f(r_{build\_factory}) \\ & + k_r * f(r_{cutting\_stitching}) + k_r * f(r_{forming\_plastic}) + k_r * f(r_{printing}) \\ & + k_r * f(r_{plastic\_coating}) + k_r * f(r_{shipping}) + k_r * f(r_{disposal\_transport}) ] \\ \\ \end{align} $$

This can be further generalized as follows, giving us a general formula for sustainability. $$ \begin{align} & \text{Let} \hspace{0.5em}E\hspace{0.5em} \text{be the embedded activities that comprise the lifecycle of the product.} \\ & \text{Let} \hspace{0.5em}N\hspace{0.5em} \text{be the non-embedded activities that comprise the lifecycle of the product.} \\ & A = E \cup N \\ \\ \end{align} $$ $$ \begin{align} s\_p = \sum_{r \in R} \sum_{a \in A} k_r * f(r_a) \end{align} $$

Efficiency

Strictly speaking, efficiency is not especially relevant to sustainability. If you have two processes, A and B, where A is much more efficient than B, but where they both emit the same amount of CO2e, regarding the contribution to global CO2e they are the same.

Now consider a scenario where B emits less CO2e than A. In this case, there may be some situations where we would prefer B. But perhaps in other situations we might want to stick with A. How might we guide our decision-making regarding efficiency?

We might consider the ratio of value (however that is defined for a product or activity) to the volume of resources that are consumed for a product or activity. This may be considered to be the efficiency with respeoct to that resource.

While measures of efficiency may be helpful when assessing a system for purposes other than sustainability, efficiency improvements on their own are not sustainable. Efficiency often drives increased demand, and increased consumption of resorces. This dynamic is known as Jevon's Paradox. Any sustainability analysis that incorporates efficiency must take this into account.

Estimation

It is important to note that sustainability analyses like those in the examples above require data across the supply chain for a product. It is often the case that some of this data will not be readily available. It is entirely appropriate to include estimated values for the data that cannot be obtained. Make sure to indicate in your analysis the data which are based on estimates, and to provide a justification for your estimations.

Opportunity cost

Sustainability calculations should always be performed on a set of alternatives for the product or activity under analysis. The sustainability analyses can be used to decide on the best alternative from a sustainabitlity standpoint.

Another way to fame this comparison between alternatives is with an opportunity cost. Opportunity cost is the value (in terms of sustainability) of the best alternative to the solution under consideration.

For example, consider a project to power a commercial building. For this project there is a fixed amount of money set aside for either a gas, solar, or wind installation. Assuming that the solar option is more sustainable than the wind option, which in turn is more sustainable than the gas option, we can say that the opportunity cost of the solar option is the sustainability value of the wind option.

Likewise the opportunity cost of the wind option is the sustainability value of the solar option. In this case we would say that while the wind option would provide sustainability benefits, it has too high an opportunity cost, and that we should pick the solar option instead.

When considering investment in climate projects, it can be especially important to consider opportunity cost. When taking into account all of the varied projects in which time, labor, and capital can be invested, it is important to think broadly about the many worthy sustainability efforts that could be options for your consideration. Especially considering the small amount of time available to avoid the worst outcomes of the climate crisis, it is important to choose wisely when selecting climate projects.

A taxonomy of sustainability

Sustainability is a multivariate concept, touching on almost every dimension of our human, technical, and environmental organizations. To organize all of this, sustainability can be analyzed along three major dimensions: environmental, economic, and social.

Environmental

Environmental aspects of sustainability include the natural resources and impacts on natural systems that are affected by a product or activity. These aspects include the following resources.

• CO2e
• Water
• Biological (Biodiversity)
• Arable land
• Minerals
• Other natural resources

Economic

Economic systems change over time. By considering the economic features at play in a system, the sustainability of that system from an economic perspective can be assessed. The economic systems and features that may be relevant for a sustainability analysis include the following.

• Capital
  • Physical capital
  • Human capital
  • Financial capital
  • Natural capital
  • Social capital
  • Intellectual capital
• Labor
  • Wages
  • Productivity
  • Training
  • Labor Markets
  • Entrepreneurship

Social

Social institutions and systems can have powerful impacts on human behavior. The sustainability of these systems can allow their benefits to extend over time. Evolving social systems into more sustainable forms can help make our organizations and institutions more robust and durable. The following social systems may be relevant when performing a sustainability analysis.

• Health
• Social networks
• Institutions
  • Social
  • Political
  • Religious

Other definitions of sustainability

According to wikipedia, sustainability is a social goal that people should co-exist on Earth over a long period of time. Sustainability usually has three dimensions (or pillars): environmental, economic, and social. The environmental dimension can include the addressing of key environmental problems, like climate change and biodiversity loss.

The Oxford Dictionary states that sustainability is the ability to be maintained at a certain rate or level, or the avoidance of the depletion of natural resources in order to maintain an ecological balance.

See also

• Sustainable Software Development
• Sustainable development
• RMI: Embodied Carbon 101
• Embodied Water
• Embodied Methane in China

Further directions

This work could be improved by the following...

• Incorporate of Lifecycle Analysis (LCA) into this framework.
• Add more detail to the descriptions of the process of evaluating the sustainability of a particular product or activity.
• Add rules of thumb for evaluating the sustainability of a product or activity.