EME 807
Technologies for Sustainability Systems

1.5. Frameworks for Applying Sustainability Principles

Basics of the Systems Approach

Building a framework for applying the sustainability principles requires some background on the systems approach. Material in this section will be necessary for further analysis of a particular engineering entity or a technology in context.

Below is a brief overview of the most important terms and concepts in the systems approach, as explained in the book by Donnella Meadows "Thinking in Systems" [Meadows, 2008]. This book is great reading regardless your professional area– so it is recommended as supplemental material for this lesson.

A system is an interconnected set of elements that is organized in a way that achieves a purpose. Three distinct entities of any system are: elements, interconnections, and purpose (or function). These ensure system’s integrity and often determine such system’s properties and behaviors as development, resiliency, self-organization, self-repair, and eventually - sustainability. You can tell that you are dealing with a system, not a random collection of components, if you can identify the mutual impacts between components and observe the outcome or behavior over time that is different from the outcomes of the separate components on their own.

For example, a forest is a system consisting of trees, soil, multiple species of flora and fauna – all of which are interconnected via food chains, nutrient flows, energy exchange, and many other chemical and physical processes. Its function is to provide environment and nutrition for sustaining living organisms and also to produce oxygen via photosynthesis. If one takes out an element out of the system (e.g., taking a certain tree species and planting it in an isolated environment, or taking an animal and placing it in a zoo), those elements would behave differently, the same as the system deprived of a certain element will be affected and will react to the change.

In a social context, for example, a village is also a system, not a simple aggregation of houses and people. Houses may be connected through the utility networks, people are connected through trade, collaboration, and social relationships. Disruption of life and function on one side of the village would cause system’s reaction and change.

In the technical world, systematic functions can be even more obvious since many engineering systems are designed by people for a specific purpose. Thus, a power plant system has a purpose to produce electric power and distribute it to a community or facility. It consists of equipment, workers, transportation means, fuel stocks, etc., all of which are interconnected in power production cycle.

Two important characteristics of systems are stocks and flows. A stock is an element that can be quantified, measured, or monitored. Sustainability of stocks typically indicates the stability of a system. In the above examples, the stocks can be: number of trees in the forest, amount of food stored by villagers for winter, or in case of power plant - the electric power generated and available for consumption. A flow is a process that either increases or decreases a stock. Flows represent inputs and outputs of a particular stock.

Let us consider the example of forest system in some more detail. The schematic in Figure 1.5 is a basic illustration how inflows and outflows can control a system stock. The size of the stock of living trees (shown by the central green box on the diagram) is increased by newly growing trees and decreased by either tree death (by natural means) or logging (human activity). The diagram's Inflow arrow shows tree growth. The outflow arrows show logging & tree deaths. If the inflows and outflows are equalized, the stock remains constant.

A central box labeled stock of living trees & an inflow arrow labeled tree growth & outflow arrows labeled logging & tree deaths
Figure 1.5. System stock illustration using a forest system.
Credit: Mark Fedkin

Flows can vary quickly; however, stocks take time to change, which affects system dynamics. Delays caused by stock reaction often serve as buffers moderating impacts to the system from internal or external disturbances.

The flow rates for input and output can be controlled or limited by the nature of the process or technology (for human activities). For the forest system under consideration, input (tree growth) is limited by the natural rate of seed germination and plant development, which in turn can depend on a particular tree species, climate, season, lighting conditions, etc. The point rate control is symbolized by the 'valve' on the diagram (Figure 1.6). Change in season or climate either open or close the input valve, resulting in corresponding increasing or decreasing inflow rate. The tree death rate is controlled by the tree lifespan, current forest density, diseases, parasites, level of pollution, weather extremes… (we do not show all possible factors in the figure, and just include a few for example). The logging rate will be determined by the level of industrial activity and current productivity, which is in turn depends on lumber market, policies allowing or disallowing logging, and technology (limiting how fast tree harvesting can be done). So, once we try to understand the interconnections, the scheme becomes more complex:

Image is adequately described in the caption.
Figure 1.6. This system flow diagram shows a central box denoting stock of living trees, inflow and outflow arrows with valves; the inflow valve is affected by climate and season; the outflow valve is affected by forest density, parasites, and pollution.
Credit: Mark Fedkin

Taking one step further, we can recognize some more mutual influences between the system elements. For instance, we may realize that a decline in the number of trees can also cause a decline in parasite population that feeds on those trees, thus the tree death rate will go down, slowing the stock decline. On the contrary, excessive tree population results in increased forest density, which can limit the amount of light available to smaller trees and limit their growth. So, this reduces the tree growth rate and keeps the stock from further explosion. Another case of stock regulation: fast drop in living tree stock can alarm the society, which would urge the policy makers to ban or limit logging in the area. All these actions form feedback loops, which are very important entities of any systems. Feedbacks and their efficiency in regulating the ‘control valves’ (input and output rates) are crucial in achieving system sustainability. We show some of the feedback loops as red arrows in the diagram in Figure 1.7:

Image adequately described in the caption.
Figure 1.7. System stock illustration using a forest system and mutual influences. System flow diagram with a central box denoting stock of living trees, inflow and outflow arrows, rate-controlling valves, and affecting factors; red circular arrows coming from the central box to valves show reinforcing feedback through climate and balancing feedback through parasite population and light conditions.
Credit: Mark Fedkin

There are two main types of feedback in system analysis:

B = Balancing feedback – opposes the change imposed on the system.
R = Reinforcing feedback – enhances the change impose on the system.

When increase in the stock increases the rate, the feedback loop is denoted with "+" sign; and if the increase in the stock results in decreasing of rate, the feedback loop is denoted with "-" sign. Such notation helps to follow the logic of the system loops, so we include the "+" and "-" signs in the diagram.

Examples of the balancing feedback in the forest system (shown with red arrows and letter B in Figure 1.7) can be a decrease in the parasite activity with decreasing available tree stock; effect of increased forest density on lighting and rate of growth; or effect of deforestation on policy (this one involves human factor and decision making). The balancing feedbacks contribute to system resiliency, i.e., the ability to jump back and stabilize after a disturbance.

Example of the reinforcing feedback in the same system can be a change of local climate and light conditions and soil loss due to deforestation, which will hamper the growth of new trees and result in further drop of stock (shown with a red arrow and letter R in Figure 1.7). Reinforcing feedbacks in part are causes of system’s growth, evolution, and self-organization. However, they can also be highly destabilizing and lead to system collapse.

Check Your Understanding

Here are a couple of other examples of feedback loops. See if you can identify them correctly.

Question #1: What kind of feedback is illustrated on the diagram below?

Flow diagram with box denoting stock of deer population and outflow arrow of deer traffic deaths; feedback arrow from box to outflow arrow is marked with + and ? signs

  1. Reinforcing
  2. Balancing

Click for answer.

ANSWER: B - balancing. The larger the deer population in a given area, the higher the probability of them being involved in traffic accidents. The traffic collisions somewhat bring down the number of deer, balancing the stock.

Question #2: What kind of feedback is illustrated on the diagram below? (Hint: solubility of CO2 in water decreases with increasing environmental temperature)

See link to text description

Click for text description. This will expand to provide a text description.
System flow diagram with three boxes denoting stocks of global air temperature, CO2 in atmosphere, and CO2 in ocean; inflow arrow to the global temperature box is marked "heating,” and the outflow arrow - "cooling.” A flow arrow comes from the CO2 in atmosphere stock box to the CO2 in ocean stock box, and this flow rate is controlled by solubility; a feedback arrow coming from the global temperature stock to solubility is marked with a minus sign; another feedback arrow coming from the CO2 in atmosphere stock box to the heating control is marked with a plus sign. The feedback loop formed by these two feedback arrows is marked with a question mark.
  1. Reinforcing
  2. Balancing

Click for answer.

ANSWER: R - reinforcing. The high global air temperature will result in lower solubility of CO2 in sea water. So, less CO2 will be absorbed by the ocean, and more of it will stay in the atmosphere. The more CO2 stays in the atmosphere, the more it causes global warming (heating).

An interesting thing about feedbacks is that they can happen by themselves, sometimes opposing logical human decisions.

Of course, the set of connections illustrated above is not even close to being complete. The real system is much more complicated. We could extend this thinking towards other environmental controls (e.g.,water, air, soil), economic controls (e.g., lumber sales), social factors (e.g., dependence of community on lumber industry and consumption), and technology, which can change both social and economic factors. However, making the system model overly complex is not practical, so it is important to set boundaries, which would help constrain the analysis and provide answers to practical questions. Boundaries are defined by the observer. Boundaries do not mean that the system is isolated from the outer world, they simply set limits; any entities beyond system boundaries are assumed to be of minor relevance and are not examined in detail until the current model requires. For example, in the forest system above, we do not consider the factors and loops controlling pollution or lumber market; however for deeper analysis, we may be forced to do so if those processes appear to strongly affect the living trees stock, which is the center of our consideration.

It should be noted that any system models are only simplifications of the real world situations, and system analysis has to be iterative to identify the most significant controls and relationships that determine system operation and stability.

Virtually any system is a hierarchy. That means that any system consists of smaller subsystems, and any system in turn may be considered as an element of a bigger system. Tree itself is a system; soil bed is a system; any biological organism is a system with its own control factors. At the same time, the forest can be considered as a sub-system of eco-region, which is in turn may be perceived as a sub-system of the planet, etc.

So, what would make the system like the one exemplified above sustainable?

A simple answer within the arbitrarily identified boundaries would be: the balance between the inputs and outputs to the main stock, so that it is not depleted or irreversibly damaged. The balance is achieved through the ‘control valve’ regulation, and the forces regulating those valves are both physical (natural laws) and intellectual (human decisions). Here, we come to an important conclusion: human decisions have to conform with the natural laws. Natural and human forces must work with each other, not against each other, to support the capacity of the life-providing stocks. This takes us back to the first Hanover Principle of sustainable design.

Systems thinking brings us to the right mindset for applying sustainability principles to a variety of case studies we will discuss in the remainder of this course. To extend your learning of the systems approach, study the following reading materials:

Reading Assignment:

Book chapter: F.M. Vanek and L.D. Albright, Energy Systems Engineering. Evaluation and Implementation, McGraw Hill, 2008 – Chapter 2 Systems Tools for Energy Systems, pp. 23-45.

Chapter 2 extends the consideration of the systems approach to some technical scenarios, specifically related to energy. It also provides some good examples of systems with feedbacks. Please read this material carefully.

This chapter is on e-reserve and is made available online through the PSU Library system. While on PSU Library website, click on Course Reserves tab and search by course number (EME 807).

Supplemental Reading:

Book: Meadows, D.H., Thinking in Systems, Chelsea Green, 2008.

This book is great reading on systems philosophy; it will really help you grasp the idea of how complex systems work. It also provides a variety of great examples. It is not available online, but you may want to check it out from a library or purchase the book online.

Global sustainability system

To set the framework for applying sustainability principles to engineering activities and technologies, let us for a while widen the angle of our view and first look at the global interconnections. Later on, when zooming in to particular processes and technologies, some of these global elements and loops may remain beyond the boundaries of our viewfinder. However, it will be important to keep these large-scale connections in mind.

See text below image
Figure 1.8. Sustainability framework for engineering.

The scheme in Figure 1.8 includes both physical and social systems in consideration. Physical systems are shown by several overlapping spheres in the upper part of the diagram: the first one is biosphere (which includes the aquatic and terrestrial ecosystems), the second one is the anthroposphere (which encompasses the agricultural, industrial, and urban systems); both of these are positioned at the triple boundary between the atmosphere, lithosphere, and hydrosphere of the earth. The sun symbol above indicates the unlimited light resource. We can expand the anthroposphere box, indicating the significant role played by engineering projects as human activity. Design and engineering result in creation of products, infrastructures, processes, and services, which all increase the extent and influence of the technical cycle. The Engineering Projects box is linked to Individuals box, meaning that technical progress is incurred by and benefits individuals in the social sphere. The feedback we can assume here is possible disturbance of the natural systems due to expansion of the anthropogenic technical systems. This expansion, in turn, can jeopardize the benefits human beings and societies derive from the environment. Individuals are given a central place in the framework since physical and social systems both contribute towards their well-being. The Social Systems box at the bottom of the diagram provides more detailed representation of those benefits, which include economic, political, scientific, legal, educational values and communications. Shown social sub-systems, such as Families, Communities, Networks, and Organizations interact to a various degree with the main social systems and fulfill certain functions. This framework diagram is very broad, and each box could be presented as a separate sub-system with its own internal connections. But this is the big picture, which allows us to contemplate on the diversity of the factors that contribute to the sustainability of human society.

Now, think where technology fits into this diagram. Virtually, it fits anywhere at the connections of the anthropogenic spheres with the physical systems. For example, through technologies, society can utilize natural resources. We also understand that technologies can do both: reconcile the processes and matter flows between the anthroposphere and environmental spheres and create conflicts between them. Thus, engineering projects undermining the resilience or adaptability of ecosystems, social systems, or individuals might bring benefits in the short term but are likely to have long-term negative outcomes. What we call sustainable technologies are designed to render the feedbacks and connections mutually harmless or mutually beneficial in the best case scenario. To assess technologies from this angle, we need to learn to recognize the feedbacks and effects they create on a large scale.