[The follow-up to this essay is found here.]
“Overpopulation is a serious problem getting worse every year.”
“Overpopulation is a myth.”
“There is no population problem.”
“There’s overconsumption, … but not overpopulation.”
“[The problem is] overpopulation in the South and overconsumption in the North.”
That’s just a sampling of the kinds of conflicting statements about population growth you can find on the Web and elsewhere. Is it any wonder the topic confuses people? Readers here should have little doubt which of the first three views I share. I would suggest, as well, that statements dismissing the population issue are often disingenuous and politically motivated.
But what about about the population versus consumption question? This issue is important, and comes up frequently. It was, in fact, the focus of a couple of Al Bartlett’s comments which I left out of my previous examination of his critique of the Scientific American issue on global warming. Specifically, he’s critical of ambiguity in Jeffrey Sachs’s handling of the population-consumption question. I’m less critical of Sachs’s handling of the issue, but Bartlett does have a point. It’s a topic which calls for clear communication. He also provides the solution to avoiding ambiguity on the issue. It is to keep in mind a simple equation: “The world’s rate of consumption of fossil fuels is the product of the population size and the average per capita annual consumption.” The formula was first published by John Holdren (1991) in his paper, “Population and the Energy Problem.” We can express it as:
E = P x e
Where: E = total energy use, P = population size, and e = energy use per capita.
Keeping this simple relationship in mind we can begin to think clearly about population growth and consumption. First, we see that our total consumption is tightly linked to population size. The two cannot be separated. Therefore the statement, “The problem is overconsumption, not overpopulation,” is erroneous. It’s both. In theory, the “problem” could be ameliorated, at least temporarily, by sufficiently reducing either population or consumption. But if the other quantity continues to grow, there remains a risk of the problem returning. Growth in either consumption rates or population is unsustainable.
In his commentary, Sachs gets at one side of this in his emphasis on the importance of rising consumption levels:
Even if the world’s population were to stabilize at today’s level of 6.5 billion people, the pressures of rising per capita resource use would continue to mount, as today’s poor and middle-income societies increase their resource use to live like the rich countries, while today’s rich countries continue their seemingly insatiable quest for still greater consumption levels.
What he leaves out is the other side of the equation. If per capita consumption rates were to stabilize at today’s levels, we would still be facing increasing total resource consumption as world population continues to grow substantially. 
What about that North-South thing?
What can we say, given this equation, about the population-consumption relationship in the North versus the South? First, as a result of the foregoing analysis, we must again acknowledge the error in one of the statements at the start of this post. The problem is not overconsumption in the North and overpopulation in the South. In both places, it’s the product of the two. And in both areas each factor is large enough to be of great significance.
But what are the implications of the differing ratios of per capita consumption to population in the two areas? Perhaps the easiest way to look at it is to notice that, under real-world conditions, if either “P” or “e” is high any increase in the other is problematic. In the South, a rough approximation is that populations are large and growing fast. Per capita consumption is currently relatively low, but is increasing and is expected to continue to do so in the coming years. Combine that with continued population growth and serious problems loom. Already, China’s population, for example, is so large that despite it’s low per capita consumption rates, it has the world’s highest total consumption of some resources. Over the coming decades, advances in clean technologies should prove essential to achieving sustainability in developing countries. But we must simultaneously attend to population growth lest the benefits of those technologies be overwhelmed simply by increasing human numbers. We must address both sides of the equation.
In the North we have more modest populations (though the U.S. is a glaring exception) which are showing less growth. Our per capita consumption rates are many times greater, however, than those in typical countries of the South. This is the situation which causes some to say the U.S. has the worst population growth problem in the world. Because of our high per capita consumption, the impact here of any population increase on natural resources is greatly magnified. For instance, with regard to oil consumption, adding one person here is currently analogous to adding about 15 in China. The problem is similar for other developed countries, though less pronounced than in the case of the U.S.
Here too, cleaner technologies will be an essential part of the solution. Moreover, the specter of climate change has brought about a new level of public awareness of the role of per capita energy use. We can hope this will slow rising energy consumption levels, at least somewhat. Clearly, though, it is imperative that we address our population growth as well if we are to have any hope of achieving ecological sustainability in the future.
The main lesson from the equation above is that we must attend both to consumption levels and population growth. To ignore either is to adopt a failing strategy. It is indisputable that neither per capita consumption growth nor population growth is sustainable.
I’ve barely touched here on the population-consumption issue. The astute reader may note that, given the facts I’ve presented, we might ignore population and still hypothetically escape catastrophe if we could develop and adopt sufficiently clean technologies worldwide over the next few decades. (In reality that is more than a tall order.) It appears, though, it’s not that simple. In this essay I’ve left out a number of important considerations which add additional weight to the importance of addressing population growth. Similarly, I’ve not addressed the observation that over the last century global energy consumption has increased more than population numbers. There again, the implications are not as clear cut as they might seem and, when examined closely, do not allow us to relax our concern about population growth. Look for those issues in an upcoming post.
[Please go here for the follow-up to this essay, which contains discussion of the second issue mentioned in the paragraph above.]
 Notice that since the bulk of world population growth in this century is expected to come from developing countries where per capita consumption is currently relatively low, the effect in this scenario, specifically on energy consumption, would be less than if population growth were evenly distributed around the world. In reality, as Sachs notes, those countries are expected to continue a strong trend of increasing their per capita consumption rates, thus compounding the effect of population growth.
Offline references: Holdren, J. (1991). Population and the Energy Problem. Population and Environment, 12 (3), 231-255.
Image source: loveitmadly, posted on flickr under a Creative Commons Attribution-NoDerivs 2.0 license