It’s generally agreed that it takes about 10,000 kilocalories per day to feed meat to one person who needs 2,500 kilocalories to survive. You should know this if you are concerned about the well being of the planet. What’s often overlooked in our perception of dietary needs is that the animals we eat need to eat and drink before we do. They need to to consume thousands of calories in order to deliver hundreds to your plate.
The primary reason you need to understand this relationship is fresh water usage. Understand water use and you begin to get a concept of the so called ‘carrying capacity’ of the planet. And having seen the arithmetic, you might wonder about the future of meat. Or the future of your children if meat is integral in their nutrition.
There are many estimates of the amount of water on this planet. The key for our biological consumption is that only about 2.5% of it is potable. We have not evolved any ability to process the saline sea water, it is in effect poisonous to us. Unfortunately, most of the fresh water is frozen in ice caps and glaciers. That’s more than two thirds of all fresh water on the planet. And almost another third is groundwater trapped in soil and rock formations. The minuscule remaining 2.5% is held in rivers and lakes and aquifers. That’s estimated to be about 100 million cubic kilometres of fresh if not always potable water.
Humans take the majority of their potable fresh water from rivers of which there’s only 2 million cubic kilometres at any given time. That’s about 2% of 2.5% of the total fresh water on this planet.
It’s estimated that mankind withdraws about 15,000 cubic kilometres of fresh water per year. We put about 20% of that into irrigation and we lose about 10% of the agri-produce between pests, harvest, transport and peeling for mealtime. If you wanted to supply a totally vegetarian diet of 2,500 kilocalories per day per person, the available potable water can only feed about 10 billion people. Suffice to say that these estimates might be in error by 10% so the 10 billion is a probable number. And if you worry that it might be 20% in error, welcome to the set of excuses that world leaders will use when it all goes wrong.
And then it gets really interesting. The maths with meat in the food chain (10,000 to make 2500) suggest that we can only expect to feed a quarter of that number (2.5 billion) if the we need four times the kilocalories (10,000 kilocalories) per day per person.
Records of these planetary water volume estimates can be found in work from 1697 by Anton van Leewenhoek. You may know him as the father of microbiology. In the 1670’s he was busy grinding glass into lenses for a microscope with which he saw the animicules that we now call bacteria and protozoa. By the late 1690s he was doing simple ‘back of the envelope’ calculations. Mathematician Joel Cohen redid the maths in 1996 and introduced meat into the diet. He wasn’t the first and his work had a remarkable consistency among the researchers who had done the calculations before him. In 1998, he also wrote that ‘Foresight and action now might make some of the coming trade-offs easier.’
You may think this is all very imprecise but on average there is a obvious problem. We expect the planet to feed 12 billion people in 2050.
Raising animals for meat would appear to be utterly unsustainable. And we’ve been in denial for the many decades in which we might have done something about managing a sensible transition.
Yesterday’s and today’s meat futures may well be costing us our children’s aspirations.
Some of my reading material:
– How Many People Can the Earth Support? by Joel E. Cohen (1996)
– Igor Shiklomanov’s chapter World fresh water resources in Peter H. Gleick (editor), 1993, Water in Crisis: A Guide to the World’s Fresh Water Resources.