People laugh at the Victorian taboo on talking about sex, while prostitution was rife in London at the time. Today, too, we have curious taboos: people don’t talk about death, for instance. But the taboo I have in mind is different: population control. It’s just not done to speak about it. But I’m going to, and I’m not sorry. It’s vital.

Back in 1972, Donella and Dennis Meadows and Jørgen Randers published a book that, even at the time, I found distinctly curious. It was called The Limits to Growth.

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It was commissioned by the Club of Rome, a non-profit think tank. It argued, in a nutshell, that a model of the Earth’s resources and human usage of them predicted, under certain scenarios, ‘overshoot and collapse’ of the whole system in the 21st century. The model was called  World3 and it contained subsystems for agriculture, industry, population, non-renewable resources, and pollution.

The basic idea of  The Limits to Growth was Malthusian, after Thomas Malthus’s 1798 book, An Essay on the Principle of Population. Malthus argued that population would continually increase; assuming the ‘means of subsistence’ started ‘equal to the easy support of its inhabitants’ – that food supply and consumption were in balance – then consumption would always tend to run ahead of food supply (and of wages), leading straight to poverty, though war, famine and disease could also intervene.

Malthus observed that either the death rate could increase to cut down a population through positive checks like famine, disease, and war; or birth rate could be lowered by celibacy, late marriage, birth control or abortion, to prevent population growth. He attacked the idea that agricultural production could grow indefinitely. He was attacked, unjustifiably, for being uncaring of the poor, and replied that it was ‘vicious and cruel’ of a government to allow population to grow without preparing to feed (and we might add, to house, educate, and care for) it, in other words for society to rely on human misery instead of proper planning for a stable and happy population.

The Limits to Growth was similarly attacked, perhaps with rather more justification. What seemed to be its ringing certainty about how we would really soon now run into unalterable limits imposed by nature was shredded by the critics. Its over-reliance on what was, after all, only a model into which one could put different numbers was in hindsight distinctly naive. By making itself look like a cranky doomsday prophecy, it became only too easy to dismiss.

But the Malthusian argument, updated a little, is unanswerable. If you have a finite planet and exponential growth – heck, ANY growth – then you must run into limits eventually. If growth is rapid, that ‘eventually’ will be soon. In 2011, Ugo Bardi’s The Limits to Growth Revisited argued that reality seemed to be following the 1972 prediction after all.

What the critics seized on in The Limits to Growth was, especially, its naive assumption that resources were known and fixed. Big Oil argued that new discoveries would (always) be made, only to find that discoveries declined rapidly, and became steadily more inconvenient, polluting or dangerous – far out at sea, high in the Arctic, or as dirty and difficult oil shale, necessitating the invention of fracking.

Big Oil and the economists argued, correctly up to a point, that when a resource becomes scarce, its price rises, and that enables formerly too-expensive alternatives to be developed. In the case of oil, that begins with deep, dangerous and dirty ways to get more oil. Failing all of those, it continues with alternatives to mineral oil, which might include synthesising oil from plant materials, or perhaps directly from sunlight, water, and carbon dioxide. Failing that, it could continue with alternative forms of energy, such as wind and solar power used with batteries, and so on, as the excess of demand over supply pushed prices steadily upwards. All of this is pretty basic economics, but it overlooks the real attachment of today’s economy to resources such as oil, and the pain that is starting to result as resources start to run short. Wars and tensions in the Middle East over both oil and water (especially for irrigation) illustrate the point.

The economists further argued that economic growth was not ineluctably tied to population growth, nor to growth in the use of resources. The economy might grow (we could phrase it today) through services like insurance, or banking, or software, or games, or videos, none of which in themselves logically entail physical resources, however much bankers build themselves flashy headquarters and huge IT centres full of hot computers and power-hungry air-conditioning systems. In theory, wellbeing and the economy could improve without using more resources. So while it looks and feels as if every industry and service depends hugely on oil today, in theory, argue the economists, you could have one without the other. So, oil, qua energy, isn’t quite the solid roadblock that it appears, nor are mineral resources like copper, or tantalum, or germanium, or gold, however vital they each may look to today’s world of electronic devices. I hope I’ve stated the economists’ case fairly.

Oil as a chemical feedstock is another matter: many years ago one of my science teachers observed that when we have burnt all the world’s oil, our descendants will bitterly regret our folly in using millions of years of chemical wealth just for energy. Paint, plastics, dyestuffs, fertilizers, medicines (yes, and pesticides and explosives) – oil has a hand in thousands of manufactured substances and materials that we all rely on every day. It sounds grim: no oil, no feedstock. Well, not quite: we already have ‘plastic’ bags made of cellulose from plants. With enough effort, chemical feedstocks like methanol can be made from wood, or carbon dioxide and water: we could one day learn to recycle carbon endlessly, and carbon will then be enthusiastically scavenged from the atmosphere as a vital resource.

Ah, carbon. The outpouring of carbon dioxide has already warmed the planet, changed the climate, moved ecological zones towards the poles, acidified the oceans. It is apparently in the process of sending perhaps half of all the species on the planet to extinction in the coming centuries. It seems incredible that such verifiable facts should be disputed; or that such urgent warnings should be ignored. But disputed they are, and ignored too, drowned out by the incessant tinnitus of wars, elections, recessions, politics, selfishness and greed, and simply the sheer bustle of daily life.

But carbon contributes to one thing that humans are definitely tied to: food. If the population rises, more food is required. Even this, though, is not a straightforward 1972-style equation, N people x C kilos consumed = F kilos of food required. If we all became vegetarians with the modest diet of a traditional Indian villager (just rice or chapatis every day, with a little oil, a few onions and chilis, rarely anything else) then the world could sustain many more of us than if we all demanded Texan portions of steak made from methane-producing cows, each animal guzzling the grain that might have fed dozens of vegetarians.

Still, for any given agricultural productivity and any given area of land there is a maximum population that can be sustained. Let’s try a thought experiment: say we achieved optimal efficiency in converting sunlight to grain, over the whole land surface of the earth, deserts, forests and all, we might increase productivity fivefold, and the productive area fivefold, for a 25fold increase. Perhaps we could grow food all over the oceans, hard as that might be; the production would double again. If we could reduce our food needs through genetic engineering (I am not advocating this) or other means, more people could be fed. Now, the human brain accounts for about 20% of our energy intake, and can hardly be changed; but let’s suppose we could halve the food used by the rest of the body, we’d then use just 60% of what we eat today: the population could increase by 100/60 or 1.66fold. So how many people would that be? Much more than now. If the current population is 7 billion then we could have 7 x 25 x 2 x 1.66 = 580 billion people on the planet; it could be more if the proportion of vegetarians increased, rather than decreasing as it is doing today. No doubt you can argue for still greater numbers.  The theoretical limit is enormous (nothing at all like the 1972 view), and full of uncertainties: still, it is an extraordinary prospect. And it ignores what we are already seeing, which is increasing shortage of resources.

But even assuming that the  agriculturalists and engineers did their work splendidly, and none of the terrible shortages of oil or water or minerals, or fights over shortages that The Limits to Growth implied ever occurred, I should not like that world, and I can’t believe you would. There would be no room for wildlife or non-food plants: no place to go for a walk in the sunshine: indeed, no call to go to the agricultural surface at all, except to drive a tractor, if humans still did such a job in a robot-rich world. For with the land all devoted to growing food, we would all live underground (but for a few super-rich, who would still enjoy unimaginable luxuries like fresh air and sunshine and flowers), work, play and probably fight down there. For any mass emergence on to the surface would spell starvation for billions as crops were crushed underfoot. Unbearable? If so, that is the limit to growth.

We could ask, why should all the planet’s resources flow to just one species, us? What makes us so special that we should take the shares of all other species, for that is what the grow-as-we-like until the  hundreds-of-billions scenario means? At the least, it is a bit selfish.

For we have one more professional to convince, after the oilmen and economists, and all the work to be done by agriculturalists and engineers to set up such a world. It’s the ecologist.

A famous book on this subject was also published in 1972: Barbara Ward and René Dubos’s Only One Earth.

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Only One Earth argued (much more solidly than The Limits to Growth) that development should be limited to ensure basic human rights, an ‘inner limit’ within the ‘outer limit’ of the Earth’s carrying capacity. Much later talk has grossly diluted the idea of ‘sustainable development’ to allow almost anything: it is much easier to claim that something is sustainable than to stop consuming more. Ward and Dubos argued for ‘the careful husbandry of the earth’, sharing wealth fairly and conserving wildlife carefully. It was pretty radical stuff for an economist like Ward. In effect, she broadened economics to include human wellbeing – a domestic and individual ‘economy’ – as well as ecology – the wellbeing of animals, plants, and ecosystems.

I would like to imagine that the arguments for healthy ecosystems rich in life of every kind are becoming obvious: I feel they are already painfully clear to anyone who looks at the question. Still, here they are, very briefly. Crops need pollinators, like bees, bumblebees, moths and butterflies, flies, beetles. Pests need to be controlled by predators, parasites, and pathogens. Materials need to be recycled by saprophytes.  We need genetic diversity – wild plants, old cultivated varieties, not to mention animals and fungi too, to combat pests and diseases, to supply unknown future crops and crop varieties, medicines, and other useful substances. In short, all ecological roles, species of every sort, are needed, not just crop plants, our primary producers, creators of food: they can’t survive alone.

More than that, more than those desperate agricultural and economic requirements, we need beauty and delight; birds, bees, butterflies, dragonflies and Komodo dragons, tigers and tiger-lilies. Without them, life isn’t worth living.

We are already in serious danger of losing all these things, as neonicotinoid insecticides join the already long list of disastrously dangerous substances we have created, manufactured in stupidly large amounts, and released onto the land with blithe ignorance (or worse, reckless lack of concern, with contrary evidence left unpublished, covered up to preserve profit). Already neonicotinoids are proving as deadly as the organochlorine insecticides of the 1950s and 1960s, that led Rachel Carson to write her 1962 classic Silent Spring.

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The veterinary drug Diclofenac has destroyed almost all the vultures of the Indian subcontinent; now its use is spreading disastrously to Africa, as countries that should know better are doing the cheapest and dirtiest thing, in the face of incontrovertible evidence of harm. We do seem to be a terribly stupid species, like Douglas Adams’s mindless military robot.

Are there limits to growth? Of course there are. It’s more than time we started acting as if there were. The taboo on population control did have some slight justification: of course we cannot want a world with compulsory sterilisations, euthanasia, even a China-style One Child policy. But there’s no need for such drastic and terrible methods. Population can be controlled far better by persuasion, by taxation, by education, by informing people of the consequences of their choices, by understanding the pressures on nature and man’s place in the world.

Let us decide how much room we want to give to forests, to prairie, to tundra, to wetlands, to deserts.

Let us decide where we want seabirds by the million to have undisturbed cliffs and seas full of fish to feed on.

Let us decide that we shall have a world full of lions and bears and howler monkeys and sparkling damselflies, of buzzing bumblebees and naturally-pollinated fruit trees, of pristine forests full of undiscovered species, rich in species and substances whose uses we have not yet even imagined.

Let us choose life, and start to live lightly on this beautiful planet.