One indicator, alluded to in the 30-75% of global energy used in metal extraction prediction, is something called ‘Energy Return on Investment’ (ERoI). One can, for example, use this to compare the efficiency of organic versus non-organic food production or the efficiency of different form of energy extraction. It works on the principles of the second law of thermodynamics, i.e. that every system – bacterium, person, animal, car, train, ship, organisation, ocean, planet, solar system etc – makes a loss whenever it processes energy.
This week the singer Miley Cyrus was named the Sexiest Vegetarian Celebrity of 2015 by animal rights campaign PETA. Putting moral or ethical beliefs about eating animals aside, our diet is one of the most significant impacts on our personal ERoI.
Like most mammals, I am about five per cent efficient, i.e. weight-for-weight, if I eat meat rather than the materials that were fed to cows, sheep, pig etc then, roughly speaking, I could have 20 meals of the materials fed to animals for one meal of the animal itself. Chickens are a little more efficient (birds do most things better than mammals except for how they breed and tend their young!) and fish are a lot more efficient because they are cold blooded. Shellfish are even more efficient again and they have the advantage in most cases that they eat stuff we cannot eat – sometimes we can’t even see what they eat. However, my EoRI is about 4:1 which means that I use about a quarter of the energy I eat in obtaining, chewing, swallowing and digesting my food.
If one takes the principles of ERoI and applies them to other things we take for granted then we start to see the difficulties. About 100 years ago the ERoI for oil was about 100:1. Today it is around 10:1 and for some forms of oil production it might be no more efficient than I am, i.e. 4:1. The worry is that, globally, we are using two to three barrels of oil for every new barrel found so the current ERoI for oil is less than 4:1 if one ignores the older and productive oil fields which will, of course, eventually run out.
Some analyses (1) reckon that an ERoI of roughly 5:1 is about the minimum needed for all our energy systems for civilization to survive in the long term. As we run out of energy and other materials we have to work harder and harder to obtain them and, eventually, we will put more energy in than we get benefit back. However, another side to this is the waste both in terms of carbon dioxide and other waste products that all this produces. We may be running low on fuel, but if the by-products are poisoning us then there is not much point in keeping on burning the fuel.
An interesting question, that perhaps one day I will try to answer, is whether this is also the ERoI of evolved natural systems, like natural ecosystems. Mammals like me are probably about as inefficient as any animal can get so I am atypical, but once one adds up all the other parts of the consumers within a natural ecosystem – the birds, insects, fish, microbes, arthropods etc – I suspect this might show that these ecosystems have an ERoI better than 5:1. A further interesting speculation is whether undisturbed ecosystems are even better, i.e. are they more efficient users of energy than disturbed ecosystems?
As an individual I am a ‘system’ that is not far off being about as inefficient as I can afford to be. This isn’t very inspiring, but if I add in the ecological inefficiency from eating meat, rather than eating the equivalent nutrition that we might otherwise choose to feed to animals, then I am definitely well below the boundary of inefficiency. Of course, when I add in all the costs of moving me around in the transport systems, the other materials I use for my clothes and all my other stuff then my efficiency drops off the scale.
Given her doubtless more resources hungry life, whether Miley’s vegetarian diet might make go some way to making her more efficient would be an interesting calculation!
- Hall, CAS, Balogh, S, Murphy, DJR (2009) What is the Minimum EROI that a Sustainable Society Must Have? Energies 2: 25-47, DOI: 10.3390/en20100025