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In the lifetime of everyone who is now over 40 the number of human beings on Earth has doubled. They are the first people ever to have lived while this happened and should this process continue the most important question facing our descendants will be how many people can the Earth support? It took about until 1830 to put the first billion humans on the planet, the latest billion took just 12 years. In 1997 there were about 5.8 billion of us living on Earth and our numbers were rising at the rate of 1.5 per cent per annum. This is enough to double the population again by about 2045, a figure some estimate to be close to, or even above, the carrying capacity of the Earth.
What happens if we go on reproducing at this rate? Optimists believe that somehow all will be well, that human ingenuity will enable us to live with the population explosion. This is a comforting thought and possibly true for those of us living in the developed world where numbers are relatively stable. However, the industrialised nations do not live in isolation from the rest and in the developing world population growth continues to be high and shows little signs of slowing down. Pessimists believe the population problem is the most important one facing the human species and see us being overwhelmed by the sheer weight of our own numbers. Could the next millennium see the end of human life on Earth?
Or is there a middle way? Joel Cohen of the Rockefeller University, New York, in a thoughtful paper in the Journal of Applied Ecology (vol 31, p.1325) suggests there may be. He believes that in the coming 50 years or so we are less likely to face absolute limits to population growth than difficult trade-offs between population size on the one hand and economic well-being and environmental quality on the other. If everyone was prepared to live on a minimum diet (about 2000 kilocalories per person per day) and be happy with quite a small living space with just basic amenities then the Earth could no doubt support a much larger population.
However, we humans seem to be programmed to expect things to always get better, politicians are elected on promises that they will, and there is a very widespread belief that living standards not only could, but should, continually rise. In the developed world it might be possible to persuade people to accept Cohen's trade-offs, reduce reproduction rates in order to live well in a pleasant environment. Perhaps, in a limited way, this is already happening. In the rest of the world, however, thanks to modern communications, people know that elsewhere things are much better and, quite naturally, they would like to improve their own standard of living. Unfortunately they continue to breed so rapidly that this is unlikely to happen. It is estimated that more than 100 million women of child-bearing age lack access to contraception. Three-quarters of a billion people were hungry yesterday, are hungry today, and will be hungry tomorrow. For them Cohen's trade-offs may not seem a viable option.
The idea that the immediate future may not be as bleak as the pessimists fear or as rosy as the optimists hope may well be valid. Human ingenuity will probably increase the carrying capacity of the Earth, it has done so before and there is no reason to suppose it will not do so again. However, unless the human race can reverse its population growth in the near future this will only postpone the inevitable. So, 2045 may not be too bad but by 2145 or 2245 there could be standing room only on Earth. If this happens then nature will solve the population problem because we with all our science and technology have failed to do so.
John Timson