There will soon be seven billion people on the planet. By 2045, the global population is projected to reach nine billion. Can the planet take the strain? The first attempt to estimate the human population may have been carried out by Antoni Van Leeuwenhoek in the 17th century. Based on his calculations, Leeuwenhoek concluded triumphantly, there could not be more than 13.385 billion people on Earth – a small number indeed compared with the 150 billion sperm cells of a single codfish.
Historians now estimate that in Leeuwenhoek’s day, there were only half a billion or so humans on Earth. After rising very slowly for millennia, the number was just starting to take off. A century and a half later, when another scientist reported the discovery of human egg cells, the world’s population had doubled to more than a billion. A century after that, around 1930, it had doubled again to two billion. The acceleration since then has been astounding. Before the 20th century, no human had lived through a doubling of the human population, but there are people alive today who have seen it triple. According to the U.N. Population Division, by the end of 2011, there will be seven billion of us.
The population explosion, though it is slowing, is far from over. Not only are people living longer, but so many women across the world are now in their childbearing years – 1.8 billion – that the global population will keep growing for another few decades at least, even though each woman is having fewer children than she would have had a generation ago. U.N. demographers project that the population may reach nine billion by the year 2045. The eventual tally will depend on the choices individual couples make when they engage in that most intimate of human acts, the one Leeuwenhoek interrupted so carelessly for the sake of science.
With the population still growing by about 80 million each year, it is hard not to be alarmed. Right now on Earth, water tables are falling, soil is eroding, glaciers are melting, and fish stocks are vanishing. If developing countries follow the path blazed by wealthy countries such as clearing forests, burning coal and oil, scattering fertilizers and pesticides, they too will be stepping hard on the planet’s natural resources. How exactly is this going to work?
At certain time periods in history, a high fertility rate was important. In 18th-century Europe or early 20th-century Asia, when the average woman had six children, she was doing what it took to replace herself and her mate, because most of those children never reached adulthood. When child mortality declines, couples eventually have fewer children – but that transition usually takes a generation at the very least. Today in developed countries, an average of 2.1 births per woman would maintain a steady population; in the developing world, “replacement fertility” is somewhat higher. In the time it takes for the birth-rate to settle into that new balance with the death rate, population explodes.
The good news is high fertility rates currently only occur in around 16 per cent of the world’s population and mostly in Africa, according to Hania Zlotnik, director of the UN Population Division. In most of the world, however, family size has shrunk dramatically. The UN projects that the world will reach replacement fertility by 2030. “The population as a whole is on a path toward non-explosion – which is good news,” Zlotnik says. The bad news is 2030 is two decades away and the largest generation of adolescents in history will then be entering their childbearing years. Even if each of those women has only two children, population will coast upward under its own momentum for another quarter of a century. One thing is certain: close to one in six of them will live in India.
The goal in India should not be reducing fertility or population, Almas Ali of the Population Foundation told me when I spoke to him a few days later. “The goal should be to make the villages liveable,” he said. “Whenever we talk of population in India, even today, what comes to our mind is the increasing numbers and these numbers are looked at with fright. This phobia has penetrated the mind-set so much that all the focus is on reducing the number.” The Annual meeting of the Population Association of America (PAA) is one of the premier gatherings of the world’s demographers. Last April the global population explosion was not on the agenda. “The problem has become a bit passé,” Hervé Le Bras says. Demographers are generally confident that by the second half of this century we will be ending one unique era in history – the population explosion – and entering another, in which population will level out or even fall.
From this, one can also draw a different conclusion, that fixating on population numbers is not the best way to confront the future. The number of people does matter, of course, but how people consume resources matters a lot more. The central challenge for the future of people and the planet is how to raise more of us out of poverty while reducing the impact each of us has on the planet.