For many decades now intellectuals, policy makers, humanitarian organizations and environmentalists have put time, money and effort into worrying about the negative impacts of humanity's ever-increasing population. It is certainly a problem worth worrying about. Everything from food and water shortages to increased disease transmissibility to habitat destruction and global climate change are made worse by overpopulation. Jared Diamond, in his excruciatingly detailed and example rich tome, Collapse, explores how human societies can fail when their population outgrows the resource base on which they depend. World population projections estimate that we will top out at 9 to 12 billion some time between 2050 and 2075. That is a lot of people for this little planet, and the risks are real and enormous. But I've been thinking about the opposite problem, one we have thought very little about, but is predicted in the same forecasts, declining population.
World population is predicted not to level off and stay at 9 to 12 billion, but to begin declining. There are two main reasons for this. First, the fertility declines that have driven the demographic transitions in rich countries are predicted to eventually reach poorer and then poorest countries as well. There is good evidence that this is already happening, as education of females and availability of information have reached places like Iran and India, fertility rates in those places has dropped very dramatically and without Chinese style coercion. Fertility rates are declining almost everywhere, even if they are still quite high in some places. The countries that undergo this transition latest are expected to still get there eventually. If the whole world had fertility rates like what the Japenese have, world population would eventually decline.
The second reason population is expected to decline dramatically is what is called population momentum. A population that had a lot of babies 20-30 years ago inevitably has a lot of babies now, because of the large number of young women reaching their peak reproductive capacity. Iran is a perfect example of this. Iran is still producing an enormous number of babies, even though per-woman fertility has declined dramatically, because there are just so many reproductive age women who were born when fertility was extremely high 20-30 years ago. Americans are familiar with this effect from the "echo boomers" the large cohort of children born in the 60s and 70s as offspring of the baby boomers. Much of what is currently carrying world population upward is this type of momentum. Much of the world still has a very young (median age in Pakistan is about 16), and therefore reproductive, population. As fertility rates decline and longevity decreases, world population is aging dramatically. Median age in Japan is about 47 and rising fast. By 2050, the UN predicts that median age in Pakistan will be closer to 35 and Japan closer to 55.
Somewhere around there world population will begin to decline, slowly at first, and then more rapidly. That is the prediction anyway. The problem is that all of our models are predicated and tested based on increasing world population. World population has increased every year since before the advent of modern science. And it is not only our demography that is based on the assumption of ever increasing population. Our entire economic system is built around the idea of ever-expanding demand driven by ever expanding population. We know how to add new housing developments, houses, cities, businesses, banks and so forth. We know how to tear down small buildings to make space for bigger, taller ones. We have no system for dealing with declining population. How should a business respond if its potential audience gets smaller every year? How should a city respond if fewer and fewer of its housing units are occupied? How should a family respond if there is no one to take over the family business or farm? How should a government respond if there are too few people to pay its taxes or fill its military?
We do have case studies of this sort of thing. Flint, Michigan is talking about condemning and leveling not just individual homes, not just whole neighborhoods, but major portions of the city that are no longer viable because the population of that city has shrunk so fast. Japan, Germany and much of the former Soviet Block are experience population decline, and adapting to it with various degrees of success. The countries that do well despite population decline seem to be those that base their economies on exports to other regions where population is still increasing. If domestic demand declines but overall demand continues to rise, it may not be such a problem. But what will happen if population is declining almost everywhere? Will people or nations increase fertility in response? Will the general lack of children induce even more people to not have children, driving fertility even further down? Will we develop economic and development structures that thrive on population decline, as our current system requires population growth?
Michigan's population decline is directly attributable to collapse in demand for Michigan's main product. Population declines in Eastern Europe are similarly caused by politial, economic and social decline. The types of population declines Jared Diamond wrote about were caused by collapses of ecologies and socieites. If we manage to get through the population maximum of the 21st century without major collapses, we may be faced with the relatively novel situation of benign decline. That can only happen if we build systems that can function and thrive with declining populations. We don't yet know how to do that.