around ten billion (give or take a billion or two, largely depending on how quickly African women receive access to adequate education and healthcare). As countries develop out of absolute poverty, first death rates decline, then birth rates, until population levels stabilise. This has been (or is currently) the experience of every nation thus far and is known as the "benign demographic transition". The demographic transition refers to the shift from high mortality and high fertility to low mortality and low fertility. It is labelled benign because it means that human populations will not continue expanding exponentially like bacteria in a petri dish (another image much loved by certain demographic doomers).
According to the best available estimates, the global human population reached seven billion individuals last Monday (give or take a few months) and continues to rise by about 10,000 each hour. We took all of human history to reach one billion around 1800. We then took a leisurely 120 odd years to reach two billion in about 1923. The third billion came in 1959 after 46 years; the fourth in 1974 after 15; the fifth in 1987 after 13 and the sixth in 1999 after 12. Since we've just taken another twelve to rise to seven billion, it may appear that human population is growing faster than ever before in history. In absolute terms, it is. The cause is not rising fertility but declining mortality. We are living longer and more are surviving childhood to raise children of their own. Yet in relative terms, we have passed our peak growth back in the 1970s. The annual rate of growth has been slowing since then as fertility rates are plummeting. Sixty years ago the average adult female gave birth to six children, now it is only two and a half. Yet sixty years ago the global average life expectancy was 48, now it is about 68, with infant mortality having declined by two thirds.
Longer, healthier lives; fewer tragic losses for parents; smaller families (largely reflecting more educated and affluent women, greater social security for the elderly and less manual labour): these are all good things. More human beings created in the image of God, more neighbours to love, more brothers and sisters for whom Christ died. This is a thing of wonder.
And yet, seven billion of us live on a single planet, with a single atmosphere, single ocean, and finite land area with limited supplies of fresh water, fertile soil and biodiverse ecosystem. Is it possible that we have too much of a good thing? For some people, this issue is "the elephant in the room" of ecological discussions (for some reason, this seems to nearly always be the phrase that is used). More mouths to feed means more food, means more land devoted to agriculture, means more forests cleared, more fertilisers disrupting the nitrogen cycle, more stress on water supplies, more trawlers scraping the bottom of the oceanic barrel, more rubbish, more carbon into the atmosphere and more demand on finite resources. We are invited to conduct a thought experiment in which every square metre of the surface of the planet contains a human: a ridiculous impossibility. So at what point do we reach too much of the wonderful thing known as homo sapiens? We love water, but too much is a destructive flood. Have we, in our enormously successful filling of the earth, now become a human inundation?
Such questions are always controversial, not least amongst Christians who (rightly) cherish children as gifts from a loving Father. But raising such questions in a simplistic manner can actually serve a dangerous hidden agenda. When you start crunching the numbers, the key figure in ecological degradation is not seven billion, since seven billion are not created equal (at least in terms of ecological impact). A single affluent Australian may have a total destructive impact on the planet that is more than one hundred or even a thousand times greater than a typical rural African. Taking carbon footprints as an example, the average US baby will be responsible for more carbon emissions in their first year of life than an average Ethiopian in their entire lifetime. The Bangladeshi with ten children may still have a far smaller drain on the planet's resources than a childless European businessman. And so, if we only look at population and ignore consumption, then the problem becomes Africa, where birth rates are highest.
Yet Africa contributes a relatively tiny share of the total demand on the earth's systems. In absolute terms and especially per capita, the developed world still bears the lion's share. Again, to pick a single statistic (which turns out to be reasonably representative of other metrics): globally, the wealthiest 11% contribute 50% of the world's carbon dioxide emissions while the poorest 50% contribute 11% (a surprising, but very memorable symmetry).
Therefore, the first issue is and must remain consumption, consumption, consumption, consumption, consumption. Or as Monbiot puts it, it's not sex, it's money. Too narrow a focus on population enables those of us who are wealthy to ignore the very real threat our lifestyles and economic system are to the planet and all its inhabitants. In some cases, a population obsession may even be a mask for xenophobic anti-immigration sentiments that have little to do with ecological concerns.
What is less often noted is that the benign demographic transition assumes that the nations currently still experiencing high fertility rates will see them decline as their affluence increases. Thus, we avoid a population explosion though a consumption explosion. The benign demographic transition may not be so benign after all if the model of development used to bring it about assumes that everyone ought to be living like us.
I do think that "the more the merrier" is true, yet on a finite planet, I believe it most prudent to pursue this diachronically, not synchronically. That is, the way to welcome the most humans onto the planet is probably not to try to do so all at once, lest we exacerbate the damage we are presently doing to the globe's carrying capacity and so reduce the possibilities of future generations. In considering this damage, population is a secondary issue, yet it is an issue nonetheless. Since we still walk a path of high consumption and great inequality (and are likely to continue to do so for the foreseeable future) then efforts to slow population growth sooner rather than later are one way of reducing the damage being done to the planetary conditions necessary for human flourishing. Of course, these efforts must remain subordinated to tackling over-consumption (which is the primary issue) and never be allowed to become an excuse to shift our own weighty responsibilities onto the poor.
Ultimately, it is possible to live a flourishing life not mired in stupid poverty without it costing the earth. A good life need not be a life of high consumption. The other alternatives are to abandon any notion of justice and expect the poor to stay poor, to institute draconian population controls or to abandon any attempt to pass on an earth anything like the present one to our children. Very significantly lower per capita consumption in the rich world is the only path that enables the simultaneous pursuit of both ecological responsibility and social justice for those living in absolute poverty in a world of seven billion and rising. Fortunately, it is also the path to greater joy.