I first became interested in population issues when a lecture on human numbers from my Tutor at St John's, Cambridge in 1959 'rang many bells'. Born of CMS missionaries and brought up in the Great Lakes Region of Africa, I have since seen how many of Africa's problems have been compounded by a four-fold increase in population. I believe that we will never meet human needs without stabilisation of human numbers, and that 'family planning could provide more benefits to more people at less cost than any other 'technology' now available to the human race'.
The Environmental Cost of Population
Unremitting population growth is not an option on a finite planet. We have just celebrated 2,000 years since Jesus' birth. Then, world population was around 200 million. Continuing to grow exponentially for just 2,000 more years would lead by one calculation to the mass of human flesh equating to the mass of the earth. By 2025, centuries before such reductio ad absurdum, our species will eliminate an estimated one fifth of all the world's life forms. Most of this destruction is not so much wanton as thoughtless. It occurs through competition from sheer numbers of humans, leading to the destruction of other species' habitats (wetlands, woodlands, coral reefs).
Too often the 'P' factor is overlooked in the IPAT equation as follows:
I = P x A x T
I is the impact on the environment of a given society/civilisation
P is population, the number of individuals in that society
A is their per capita affluence (with consequential invariable 'effluence' = pollution and resource/energy consumption per capita)
T is a composite factor accounting for the per capita impact of the technologies in use (lowered by 'greener' technologies, with lower energy use and maximum recycling)
The Need to Stabilise Population
In many resource-poor countries the people deserve that the A-factor, affluence, should significantly increase, along with an increase in per capita disposable income. Although this will mean greater energy consumption and adverse effects on the local and global environment, this is something the 'haves' of the world must accept - and Christians rightly take a lead here. But it makes global reduction in the average per capita A-factor even less probable. There are strict scientific limits to the reductions possible in the T-factor, so it would seem logical that Christians should have a positive view on stabilising (rather than just adapting to) the P-factor, population, the only other factor in the IPAT equation.
Fortunately, birth rates are declining in most countries (small thanks to the opponents of voluntary birth control services). But all of tomorrow's parents are already born, so many in number that even if their family sizes were improbably to average two, population growth would not cease until about 9 billion. This is a 50 percent increase on October 1999's 6 billion and it will occur despite the ravages of AIDS. The choice about stabilisation is not whether, but when - and at what total. If we wish to preserve a halfway tolerable global environment, and achieve a halfway decent life for those in degrading poverty, this must be as little above that unavoidable 9,000 million as possible.
The Vicious Cycle of Population and Poverty
If we see population growth just as something to adapt to, a vicious circle emerges: population increase maintains poverty, and poverty maintains population increase.
Population increase maintains poverty, because the finite 'cake' of any resource-poor country has to be divided amongst ever more individuals. Without stabilising the number of individuals to share it, an increase in a country's GDP can produce (as in my home country of Rwanda) a fall in the per capita GDP and more poverty. The increase in population keeps wiping out the gains, whether in agriculture, education and literacy, or healthcare.
In turn, poverty maintains population increase, because in rural poverty 'every mouth has two hands'. The labour of each new child in the family is welcomed, especially in the absence of social security for sickness and old age. High child mortality also tends to reduce interest in birth planning.
Ultimately, the medical and social consequences could be catastrophic. Hence my Kew Gardens 2044 Time Capsule, which included an apology. We have not inherited the world from our grandparents, we have borrowed it from our grandchildren. My prayer is that they should not need to accuse us of damaging their loan beyond repair.
Short of that, while definitely not the cause of all major world problems, increasing population is the unrecognised multiplier of most. Some were in our recent BMJ editorial: 'poverty and malnutrition, resource shortages and pollution, the loss of bio-diversity and wildlife habitats, increasing global inequality, and conflict and violence'. Medical consequences are obvious within that list, others are predicted from global warming (more humans burning ever more fossil fuels).
Not Coercion, but Planning and Social Justice
I doubt Maurice King's notion that the USA is in some kind of alliance to downgrade the importance of population so as to continue, as now, profligately consuming resources. However I am perturbed by the prevalence of ostrich-like laissez-faire views, given the 200,000 additional individuals that humankind somehow has to care for with each new day. The notion that we need do nothing to regulate population  is dangerously complacent.
On the other hand, I am strongly opposed to every agency, government or individual that practises or permits compulsion, whether overt or covert, regarding birth planning methods or family size. I therefore teach avoidance even of the word 'control', after 'population' or 'birth'. I reject one-child policies and coercion in any form. We should not so much count people as ensure that people count.
I believe the best way for the world to deal with the 'problem' of population is through the relief of poverty and all its consequences combined with the means for women to achieve their human right to control their fertility. In short, we must work for birth planning and social justice with equal vehemence! Wealthier smaller families mean less population growth, fewer to share the 'cake', and hence still less poverty and even smaller families. The vicious cycle of population causing poverty and vice versa can then become a virtuous, upward spiral - as has happened, with average family sizes dropping below three in countries as different as Thailand and Costa Rica.
'Social justice' includes many components: education, reproductive health care, and women's empowerment. If we take care of the people, the population will take care of itself. But part of that 'taking care' involves ensuring that people can enjoy God's gift of sex within marriage while at the same time being able to plan the number and spacing of their children. For this they need universal, easy access to culturally appropriate reversible contraception methods through subsidised user-friendly services. We know from large scale social surveys of 240,000 women in 38 countries [5,6] that it is now a myth that most women in the South do not want to plan their families. We are failing to push at an open door! Doing so could greatly reduce both maternal mortality and the abomination of 50 million induced abortions annually.
In the real world it is medically necessary to make methods of contraception available to unmarried as well as married people. However I dissociate myself from any agency or individual which promotes intercourse outside marriage, and from policies or practices that undermine the family as our Designer's intended setting for child-rearing.
Many non-Christians see Christianity as the problem - seeing in Genesis 1:26,28 a biblical justification for riding roughshod over the biosphere - a licence for humankind to exercise 'dominion over' the world rather than (the more correct) 'stewardship for' the world.
Yet if one looks again it is striking that God exhorted plants and animals to be fruitful and multiply before giving that instruction to us humans. The Creator did not and does not intend us to multiply so much that we prejudice the fruitfulness of all his other creatures. This would be contrary to his immanent nature.
I believe there is implicit in the Bible another attribute of our God, additional to his omnipotence, omniscience, and omnipresence; namely omni-common sense! Population growth has happened as a result of vastly improved survival through modern medicine but without adequate birth planning. If obeying the 'multiply' instruction would lead to human numbers which exceed the carrying capacity of the land available - and so wipe out millions by starvation, disease or violence - godly common sense suggests this is not obeying his other instruction to us and the rest of creation to 'be fruitful'! Christians should be enthusiastic supporters, often through their own tithing, of voluntary birth planning within God's ordinance of marriage - worldwide. I believe this is squarely within God's plan for these times.
We must ask ourselves new questions relating to the two great commandments of Jesus:
First, 'Love the Lord, your God': are we really doing that if we do not cherish and care for his creation - just as we would for something made by a human loved one? Our love for God should surely ensure inter alia that there are not more of one species (humans) than can possibly live full lives, while permitting the survival of all his creatures.
Second, 'Love your neighbour as yourself': should we not as well as loving our overseas neighbours, also love our future neighbours? And doesn't this involve helping to ensure that there are not ultimately so many future neighbours that God's world becomes uninhabitable?