The Planet's Carrying Capacity

Many believe that we are undermining the very life support systems that sustain us. Like bacteria in a petri dish, our exploding numbers are reaching the limits of a finite planet, with dire consequences. Disaster looms as humans exceed the earth’s natural carrying capacity. Clearly, this could not be sustainable. Many have learned the classic mathematics of population growth — that populations must have their limits and must ultimately reach a balance with their environments, it’s physics, after all, there is only one earth! "Carrying capacity" refers to the number of individuals who can be supported in a given area, within natural resource limits, and without degrading the natural, social, cultural, and economic environment for present and future generations. The carrying capacity for any given area is not fixed. Carrying capacity is not a fixed number. Estimates put Earth's carrying capacity at anywhere between 2 billion and 40 billion people. It varies with a wide range of factors, most of them fitting under the umbrella of "lifestyle." If humans were still in the hunter-gatherer mode, Earth would have reached its capacity at about 100 million people. With humans producing food and living in high-rise buildings, that number increases significantly

A good way to understand the flexibility of Earth's carrying capacity is to look at the difference between the projected capacities of 2 billion and 40 billion. Essentially, we're working with the same level of resources with both of those numbers. So how can the estimates swing so widely? Because people in different parts of the world are consuming different amounts of those resources. Basically, if everyone on Earth lived like a middle-class American, consuming roughly 3.3 times the subsistence level of food and about 250 times the subsistence level of clean water, the Earth could only support about 2 billion people. On the other hand, if everyone on the planet consumed only what he or she needed, 40 billion would be a feasible number. As it is, the people living in developed countries are consuming so much that the other approximate 75 percent of the population is left with barely what they need to get by. Ultimately, the idea is this: If everyone on Earth can manage to do more with less, we'll be back on track to Earth's indefinite carrying capacity.

A Scottish shooting estate manager maintaining a population of deer will want to know how many deer could be supported on that patch of land. Having an idea of carrying capacity would tell him, as a rough guide, whether his land is underpopulated (in which case the population would be expected to grow) or overpopulated, which could happen if too many deer were competing for the same resources. Some wildlife populations fluctuate widely in size and exhibit a tendency to “overshoot” carrying capacity, in which case natural mechanisms—like starvation or increased predation—kick in to reduce the population size. Overpopulation, for a wildlife manager, would indicate a risk of disease or damage to the resource base from overgrazing. The game manager might decide to allow hunters to harvest some of the animals in order to bring the population back down to a sustainable level; the carrying capacity. Shouldn’t we take steps to manage the human herd?

This is nonsense. These claims demonstrate a profound misunderstanding of the ecology of human systems. The conditions that sustain humanity are not natural and never have been. Since prehistory, human populations have used technologies and engineered ecosystems to sustain populations well beyond the capabilities of unaltered “natural” ecosystems. We transform ecosystems to sustain ourselves. This is what we do and have always done. Our planet’s human-carrying capacity emerges from the capabilities of our social systems and our technologies more than from any environmental limits. The idea that humans must live within the natural environmental limits of our planet denies the realities of our entire history.

There is no environmental reason for people to go hungry now or in the future. There is no need to use any more land to sustain humanity — increasing land productivity using existing technologies can boost global supplies and even leave more land for nature — a goal that is both more popular and more possible than ever.

An oft-cited piece of country wisdom is that you can feed a family of four on an acre of land, more or less, give or take. If you allow 4 people per acre, this gives you 988 people per square kilometre. So if you find the maximum cultivable or productive area of a given country, and multiply that by 988, you can get an approximation of the maximum sustainable population (MSP) of that country. The maximum cultivable area of the UK - meaning land good for annual crops like wheat or permanent crops like fruit trees - is just 23 percent of total land area, or around 56,600 sq.km. This might not sound like much, however, when you times this by 988, you get an MSP of 55,924,752. This is rather more impressive, though still shy of the current UK population estimate of 65 million. However, we have not included pasture land, currently used for dairy and beef cattle, sheep and goats. The main thing wrong with this land, from an arable point of view, is that it's not flat enough for tractors and combine harvesters. Given that pastured beef consumes around 20 times the energy it produces (grain-fed beef is around 40:1), it could make sense to convert this pasture to intensive allotments which would yield on average 20 times more food. If you include this land, the total farmable land area goes from 23 percent to 75 percent. Even this does not include woodland, which constitutes 11 percent of the remainder, and which could, in theory, be turned to good account using well-established 'wild farming' techniques like permaculture and forest gardens. Most of what's left is lakes (fish-farming?), parks, golf courses and mountains. Urban development, cities, roads, buildings etc only account for about 4 percent.So if push came to shove, the tiny islands of Britain could convert 86 percent of their land to agriculture. On a land area of 241,590sq. km this gives a theoretical MSP of 238,631,640, near enough the population of the USA than of Britain. First, could an acre really feed 4 people, year in, year out? Farmers in Britain with smallholdings say they can be generally self-sufficient on vegetables using around an acre, but there is a limit to what you can grow in the British climate, and soil quality, light, drainage and other variables will also affect yield. And you also need to let land lie fallow or else exhaust it or drench it in polluting nitrate fertilizers, so it would be wise to slash that figure in half. But even so, and even allowing some meat farming so people can still enjoy the odd hamburger or sausage, it's hard to see how there's any obvious danger of famine. Rather than being a basket case, socialist Britain might even be a net exporter. Currently, the UK produces about 75 percent of its food and imports the rest. But it imports things you can't easily grow here, mostly Mediterranean fruit and veg, coffee, rubber and wine, and exports things the world enjoys, mainly whisky. Imports come from around 28 countries, and the government view is that the more sources you have the better since your supply is less likely to be interrupted. But this may not hold when socialism is first established, because global priorities may be more concerned with feeding starving people elsewhere than providing Brits with their morning orange juice and cappuccinos. And though it may be cheaper in capitalism to ship tomatoes from Spain than grow them in UK greenhouses, the same economics may not hold in a non-market moneyless economy. In short, though socialism will be global, it will be smart for people to produce as much as possible locally without relying on fleets of container ships. A similar MSP calculation gives Ireland a potential to feed 2.5 times its current population, while the USA could feed its people 5 times over on arable land alone, without considering the vast cattle ranges. 

The same story is true pretty much everywhere. People don't take up much space at all. It's capitalism – and the rich - that engulf resources and create misery. Socialists fully recognise the need to protect the life-support system that sustains humanity. 

Adapted from a Socialist Standard article