The Second Law of Thermodynamics says:

The entropy of a closed system always increases.

Indulge me here for a minute…

Entropy is a measure of disorder. My favourite analogy for the Law is a our toddler Charlie in our living room. Disorder always increases unless an external source of energy (ie a parent) intervenes and tidies up.

If we use entropy as a measure of pollution, the Second Law tells us that unless we use an external source of energy (eg solar), then in the long run we are, frankly,  in deep doodoo (that’s a specialist scientific term). Every time we want to do something useful – make electricity, move a car – it will always involve creating more bad stuff than good.

Nature gets over this by using solar/gravitationally-powered cycles such as the carbon cycle and the water cycle. By opening up the system to these external sources of energy, nature can be sustainable.

Why am I lecturing you on Thermo? Well, the Second Law is a wonderful rule of thumb when sizing up potential sustainability ideas.

The Second Law rules out perpetual motion machines and adds a level of cynicism to my assessment of technologies such as ground source heat pumps and carbon capture and storage. Both of these attempt to decrease the entropy of the system (turning diffuse heat into concentrated heat and concentrating a diffuse gas) and are often prey to ‘unexpected inefficiencies’ when implemented in practice.

The Second Law pushes us to emulate nature and use renewable energy and the circular economy concept to build a sustainable economy.

Not bad for eight words – that’s why I think of it as the First Law of Sustainability.