Some 10,000 years ago, at the beginning of the Holocene geological age, there were only around five million of us on the planet. Although humans had a significant impact on the natural world – by using fires to clear forestry or hunting large mammals to extinction – their effects were localised.
Boy, have things changed. In 1900, there were 1.6 billion of us; by 2000 the global population had shot up to 6.1 billion. Last year, we passed the seven billion mark, and best estimates have us reaching the nine billion mark before 2050.
The sheer number of people has profoundly changed the global landscape, as we convert vast tracts of wild vegetation to agricultural or grazing areas, for example. Fishing on an industrial scale to provide for billions has dramatically altered marine diversity. Individual farmers breeding livestock or keeping chickens, when multiplied by millions, have caused biodiversity changes in which more than 90% of the weight of all terrestrial vertebrates is now made up of humans and the animals we've domesticated. The quest for resources to supply us all with materials and the trappings of life has depleted the forests, polluted rivers and soils and even carved the tops of mountains. And the fuels used by each of us for energy have produced combined emissions that are already altering the planet's climate.
By 2050, it is estimated that we could triple our resource consumption to a whopping 140 billion tonnes of minerals, ores, fossil fuels and biomass per year. Our food requirement alone is expected to double by then.
Is our ever-increasing human population propelling us to our doom? Is there a limit to how many people can be sustained on a finite planet – and, if so, have we already passed it?
It’s not the first time we’ve been presented with this doomsday scenario. More than two centuries ago, when the global population was around an estimated one billion, the British social economist Thomas Malthus issued dire warnings about the risk of population exceeding resource limits. In 1798, he advocated limiting family size and postponing marriage. (As one of seven children, he practiced what he preached by only having three of his own.)
Since Malthus, there has been no shortage of economists, environmentalists and demographers predicting humanity's collapse through famine, wars and epidemics, if we don't check our population. Some environmentalists even go as far as to say it is morally wrong to have children at all.
So far, the doomsayers have been proved wrong: tragedy has been averted through better technologies, the invention of artificial fertilisers, improved medicines and other rescuing remedies. Indeed, there are some examples of where population increase has led to resources being better conserved and managed. For example, Machakos in Kenya, whose population rose to 250,000 – with accompanying resource over-exploitation, denuded hillsides and soil erosion – actually improved when its population rose still further. The extra labour available meant hillsides could be restored and soil erosion tempered, and Machakos is now home to 1.5 million people.
However, whether this improvement can be solely attributed to the increase in population, and whether it can be replicated elsewhere, remains debatable. Examples like Machakos are few and far between – outweighed by the far greater number of societies that have collapsed due to unsustainable resource use, driven by overpopulation.
However, around 1968 (global population count: 3 billion), when Paul Ehrlich’s book The Population Bomb warned of mass starvation due to overpopulation, the rate of human population growth peaked – and then declined. The growth rate has dropped 50% over the past 40 years, as the average woman in developing countries (outside of China) now has three kids, rather than six.