Sustainability and Systems Theory

After a long hiatus (real life gets in the way sometimes...) I'm back.
Recently, I've been studying the flows of energy within human systems (for example, cities), and the consideration of these energy flows often comes back to the concept of entropy and sustainability. A lot of this relates to systems theory, which is complex and I am by no means an expert, but this blog intends to act only as an indroduction to some of the issues and concepts surrounding renewable energy and sustainability.

Entropy is a difficult concept to grasp. An overview can be found here. One way to view it is the overall disorder or 'useless energy' within a system. An increase in entropy means an increase in disorder, and more energy is lost into forms where it is no longer useful - for example, low grade heat or sound. The first law of thermodynamics states that energy cannot be created or destroyed - only transformed into other forms. An increase in entropy can therefore be seen as the transformation of useful energy into useless energy - forms in which it can no longer be transformed back into useful energy.

Life causes a local reversal of entropy: an organism is a highly organised system, in which entropy is decreased (useful energy is collected). Similarly, human civilisation can be viewed as a biological/ecological system - cities cause a local decrease in entropy as energy flows into the city in the form of, for example, fuel.

However, this local decrease in entropy occurs at the expense of the surrounding environment: entropy increases in the surroundings as energy is collected from the environment and concentrated in the system. As energy is used in the system, it is eventually transformed into 'useless energy' - usually waste heat.

As our civilisation has developed technologically and economically, we have been maximising our energy throughputs, and so speeding up the transformation of energy into 'useless' forms. In other words, we have caused the acceleration of entropy within the earth atmosphere system - this indicates an "unpromising resolution for the future of life on earth". [1]
This would seem to indicate that it is not possible for any system to be truly sustainable.
The definition of sustainability is that a system operates in a way in which its functions are not limited, while not hindering the future operation of the system. If, in any system, there is always a loss of energy to useless forms (an increase of entropy), it would seem that eventually there will come a point where all energy is in a useless form. This is indeed the case.
To us, on earth, our 'closed' system of the earth-atmosphere is contstantly being 'topped up' with fresh energy from the sun. But the sun itself is subject to entropy, and so eventually it too will die.
There is a theory as to the final end of the universe based on this idea: the heat death of the universe. This is about as depressing as it sounds - eventually the universe will run down, as all of its energy is converted over time into heat. The heat will dissipate, equalising across the whole universe. At this point, there is no more 'useful' energy left.

The good news is that on our sort of timescale, the sun will continue to provide useful energy. However, it is still likely that we could exploit all the energy within the earth-atmosphere system; the point at which all natural resources have been used up, and we are relying entirely on the sun.


Systems theory identifies a successful system as one which has maximised its energy efficiency. A biological example of this can be seen by looking at the oldest animals on earth: reptiles. They have low metabolisms, high efficiencies in their use of energy. In contrast, the 'younger' mammals have higher metabolisms and lower efficiencies. The feedback process of evolution has allowed the reptiles to maximise their efficiency - a process which is still occuring in mammals.
Comparing the human civilisation system to these biological ones, it is clear that we have a very high metabolism: in the stage in which we are at, we have maximised our energy throughputs, without improving our energy efficiency. We are, then, at a turning point of sorts. We must now act to maximise our energy efficiencies to slow the increase of entropy in the earth-atmosphere system - otherwise we will be hastening the point at which entropy within our environment is too high for our civilisation to continue.

[1] Theory of urban energetics and mechanisms of urban development - Huang, S., Chen, C.