Sustainability and the Laws of Thermodynamics: A Primer
Last week somebody responded to the edition of Ask Gareth on zero waste by saying zero waste was thermodynamically impossible. My heart soared as I love a bit of thermo, and a bit of a debate, so I thought I’d expand a little on Sustainability and thermodynamics, and explain why this comment is incorrect.
Way back in 1998 when I was a newbie researcher exploring Sustainability as a concept, I was wading through a mountain of heartfelt waffle on the subject when I stumbled on an explanation in terms of thermodynamics. It made complete sense to me and something clicked. When I explained this to my project supervisors, one of them said thermodynamics was for chemical reactions, not for the whole planet. I persisted as I like nice neat explanations for big complex situations and I won him over. To this day I tend to fall back on the laws of thermo to help me spot perpetual motion machines and other blind alleys, and remind me of the big Sustainability picture.
There are four Laws of Thermodynamics, and a gazillion definitions of each, but for our purposes we need the first and second Laws which can be expressed simply as:
First Law: energy and material can be transformed from one form to another, but cannot be created or destroyed.
Second Law: the total entropy of an isolated system always increases over time.
As entropy is a measure of disorder (read: pollution, dissipated resources), the two are often interpreted as us being stuffed in the long term – inevitably the world will grind to a halt. This is the interpretation of zero-waste-impossible guy. But the crucial bit is the ‘isolated’ caveat – the earth is not isolated, rather it receives huge amounts of external energy in the form of solar insolation and gravitational pulls.
Earth’s natural systems have been pretty sustainable for the last billion years as they follow two important principles to comply with those two laws:
1. there is no waste, all materials and nutrients are endlessly recycled;
2. those cycles and everything else, are powered by those external energy sources, most notably via photosynthesis.
Translating these into industrial parlance and you get the circular, zero waste economy and the renewable energy industry as models for a sustainable economy.