The fact that the mid-range projections for world population rose by nearly a billion people this week should have garnered a lot more attention than it did. The UN offers biennial updates of its world population estimates, and for the last few years, the mid-range (ie, the most likely scenario) has suggested that the world will peak around 9.2 billion people near the middle of this century, and then slowly begin to decline. The 2010 estimate, however, found that the decline is no longer considered likely, and that by 2100, the world may have as many as 10.1 billion people.

This raises a whole host of issues, which I’m going to consider over the next month. Raj Patel has already usefully offered one answer (which I don’t wholly agree with, but it is interesting) to the question of whether we could feed 10 billion people. But first I want to ask whether the population estimates themselves are realistic.

Now it is important to remember that these aren’t flat numbers and this isn’t a census. It is an estimate, with a range of possible outcomes based on a whole host of variables, including behaviors, death rates, education, etc…. Moreover, the longer range (2050-2100) numbers are more speculative, because the people who will be giving birth then have not yet been born. On the other hand, many of the people who will be having children between now and 2050 already are born – so we have a sense of those people. It is certainly possible they could choose to have more or fewer children than demographers estimate, but the basic number of potential parents is close to being fixed.

Much of the change predicted is projected to occur in Africa, where the demographic transition has been taking place, but more slowly than in parts of Asia and South America. The other major factor that is expected to shift African demographics is a continued expansion of access to HIV drugs, thus shifting lifespans from in the 40s and 50s back towards the 70s. Globally, the report finds:

Life expectancy is projected to increase in the three groups of countries considered. In 2005-2010, average life expectancy at birth was lowest among the high-fertility countries, at 56 years, mainly because many of them have generalized HIV/AIDS epidemics. Nevertheless, given the advances made in reducing the spread of the disease and the expansion of antiretroviral treatment, the projections assume a continued decline in mortality rates from HIV/AIDS as well as from other major causes of death. Therefore, the expectation of life among high-fertility countries rises to 69 years in 2045-2050 and to 77 in 2095-2100.

Among intermediate-fertility countries, average life expectancy was 68 years in 2005-2010 and is projected to rise to 77 years in 2045-2050 and 82 in 2095-2010. Lowfertility countries tend to have, as a group, higher average life expectancy. It was estimated at 74 years in 2005-2010 and is projected to rise to 80 years in 2045-2050 and to 86 years in 2095-2100. Globally, life expectancy is projected to increase from 68 years in 2005-2010 to 81 in 2095-2100.

One of the things to know about this report is that while it does in a limited way take climate change into account, it does not take resource limits into consideration in a serious way, and it generally presumes levels of economic growth and globalization will continue. As much as I would love to see anti-retroviral drug access expand in Africa, and continued lifespan increases across the globe, I’m not at all sure that I think these presumptions, particularly the assumption of continued economic expansion and access to the trappings of middle class life for more people are realistic. To the extent that population growth has depended on fossil fuel growth and the economic expansion it fuels, we must ask what the future of population is in a world of material limits.

We should note, for example, that while lifespans have continued to increase in the Global North, poor areas of the US have for the very first time in recent years show signficant declines in overall lifespan in its poorest areas. Other poor areas have seen no increase in lifespans. It would suggest that if there is an era of economic stagnation or decline, projections for the Global North or parts of it may be inaccurate. Indeed, we have seen the ways that collapse affects lifespans after the Soviet collapse, where lifespans for men dropped back into the 50s.

Access to anti-retrovirals, so desperately needed in much of Africa, has expanded dramatically. It is hard to write this, because this has been such a necessary gift to societies being destroyed from the inside out – suggesting it might not last is actively painful to me. And yet, access to HIV drugs depends heavily on industrial supply chains, on a nascent pharmaceutical industry in Africa that relies heavily on imported raw materials, and on the importation of generic drugs in quantity over long distances. More fundamentally, they rely heavily on international aid.

I am not expert enough in the issues of drug manufacture and distribution to argue that the drugs will not be available in an era of economic decline – indeed, I can’t but hope they are – but it is certainly a vulnerable spot, because it depends heavily on both the affluence of the Global North, which has a long history of abandoning its aid commitments when life gets inconvenient or economic crisis hits (consider the abandonment of the commitment to alleviate the emergent food crisis of 2007-8) and also on manufacture, shipping and transportation that are heavily energ intensive. If I were queen of the world, manufacturing HIV drugs in Africa would be one of those best use things that one reserves oil and other resources for. Historically speaking, Africa’s needs have often come last, and when oil prices spiked in 2007, many African nations saw disruptions of needed supplies.

If lifespans are in question in some measure, are birth rates? Again, there are many variables here, but what we can say is that periods of cultural and economic crisis do tend, at least in the Global North and often in the South as well, to send birthrates rapidly downwards. Consider the drop in TFR in the US during the Great Depression, which was dramatic – couples couldn’t afford to marry, married couples delayed childbearing. Moreover, the most economically productive people in any economy tend to be those of childbearing age – massive economic stress on them tends to result in reduced childbearing at least in nations where children represent an economic burden.

The situation is more complicated in poor nations with high fertility, where often children are one of the few economically valuable assets a family has. In Nigeria, for example, a child begins to produce more than he consumes by eating by the time he is six years old, and by 12, may produce as much economically as an adult. Add to this the high death rates and lack of security for the elderly and for women and you see that economic value of children in difficult times is somewhat different – for example Vandana Shiva and Maria Mies point out in _Ecofeminism_ that an Indian Woman in the rural areas has to have five children in order to be sure that when she is 60, she will have a living child able to support her. But even in the world’s poorest places, the demographic transition is ongoing and crises tend to have a negative effect on overall childbearing.

The one thing we can be nearly certain of is that this will be a century of crises – and while the exact nature of the economic, climate and energy crises we face is up in the air, and I do not make any claims about what effect they will have on human fertility, it is worth asking at least why the UN analysis presumes the rates of growth it does, and whether this analysis would more wisely include the problems of resource limitation.

Resource limits are a lousy way to solve the population problem, obviously, and no one advocates for them. But we need good data on population, and the problem with the UN projections is that they leave out large parts of the puzzle. It is certainly possible that we will reach 10 billion people – but we are not making our assumptions based on the real underlying ecological, energy and economic limits we are facing, so we simply don’t know.