I’ve been doing a little reading around population issues for a project I’m working on. One of the questions that regularly comes up is this one, how many people can the earth support? It’s the question behind the Optimum Population Trust, who campaign for population policies.
Their answer? Around 3 billion, once you’ve navigated the caveats.
As it turns out, it’s a rather old question. Antoni van Leeuwenhoek, better known as the inventor of the microscope, made the first known estimate of the earth’s carrying capacity in 1679 in Holland. He reckoned that a population of 13.4 billion people could be fed and clothed without any trouble. A 1765 estimate from Germany comes in at 13.9 billion, another from mapmaker Thomas Templeton at 11.5.
Abraham Lincoln took a guess at the US carrying capacity in his 1861 State of the Union address. At an ideal ’73 and a third’ people per square mile, his estimate was 217,186,000.
More recently, the Limits to Growth report pitches a global estimate somewhere nearer 7 billion. A review of 65 different studies in 1995 found estimates varying from less than 1 billion to over 1 trillion.
Wherever it might fall, it’s a well-established ecological principle that there must be a ceiling to human population. Carrying capacity is the number of individuals of a given species that can live within the limits of a specific habitat. Every species has its own space requirements for food and water, territory and so on. If it’s true for every species and every habitat, it has to be true for humanity too. We’re remarkably adaptable, and global trade means we don’t necessarily have to respect the limits of individual nations, although it would be wise to be more independent than we currently are. But just because we’re succesful doesn’t mean that we’re immune to the laws of ecology. It would be a real tragedy if our history of defying estimates of optimum population made us so complacent that we thought infinite growth was possible.
There are limits, this much we know. But where they lie is anyone’s guess. Joel Cohen, in his book on this question, maps the various estimates and reckons there are two clusters of guesses, one around 7.7 and another around 12 billion, but otherwise there is no consensus. Despite calling his book How many people can the earth support, he refuses to answer the question: “How many people can the Earth support? The question is obviously incomplete. Support with what kind of life? With what technology? For how long? Leaving what kind of Earth for the future?”
Every estimate of the earth’s carrying capacity has to make a judgement about a life worth living, about levels of consumption. The calls to stabilise the population at 3 billion pre-suppose nothing less than a consumerist European lifestyle. The moment you start talking about ideal populations, what you’re actually talking about is an ideal level of consumption.
More importantly, even if we could get an accurate, once and for all answer on how many people the earth can sustain, then what? Even if we could get an international agreement to reduce population towards it, it would still take hundreds of years. We should stabilise the population as best we can and seek to reduce it in future, but the whole idea of a distant ideal target is a pointless distraction from what we should be doing right now.
The population we have is a fact. Whatever we do, a certain amount of growth is locked in over the next couple of decades, so population growth is a fact too. Rather than agonising over an ideal number, we should be concentrating on how we live together on a crowded planet. How do we provide everyone’s basic needs? If further growth is inadvisable or impossible, then surely redistribution is the only way to end poverty – let’s talk about that, in our disastrously unequal world. Let’s talk about what an ideal level of consumption might be, as resource depletion becomes increasingly obvious. Let’s talk about contraction and convergence, the right of every person to emit an equal share of greenhouse gases.
Instead of an Optimum Population Trust, we need an Optimum Consumption Trust.
The Earthbound Report 
To add my sermon to this question: when I still was a student with the Physical Geography Dept. at the University of Münster/Germany, we attempted a systems analysis to determine the long term human carrying capacity of the Earth, based upon the then (1991) resource consumption and emission levels of the United States. Depending on the parameters we fed in we arrived at numbers between 200 and 600 million, the upper range approximately being the current population of the EU and US combined. The calculations included critical loads and levels and other pressures on ecosystems but obviously did not take into account economic growth.
Really nice post Jeremy, though I do think population and consumption go hand in hand so I’d settle for a Optimum Population and Consumption Trust.
In many ways this is very similar to Climate Change ethics and how we use/share global resources and that it is quite pointless to save someone’s life from climate catastrophes to just have them die from preventable poverty related causes.
Anyway we already have environmental footprints/planetary resource boundaries, Gross National Happiness and the ‘How Much is Enough’ push, but like action on climate change many will just see this as a socialist plot to redistribute wealth. I’m not sure that those that are indifferent or against resource justice will see the need to change before it is too late, or in fact they will instead just go down the nationalist route and will prefer to fight over what is left. Maybe we can use the GFC and Peak Oil as an opportunity to push the Transition Town like movements as a viable alternative to society’s growth/consumption addiction.
Your incorrect, there is approximately 1 billion more people living on earth then the predicted amount and if you disagree with me, feel free to reply (preferably by email)