Sustainable future
Since we’ve created multiple crises in the natural world, it’s time to talk about overpopulation, writes Jack Santa Barbara
November 2022 recorded the largest human population ever, 8 billion and counting. Comments from the United Nations and other sources were generally celebratory.
At the same time, Elon Musk and others have warned that the falling fertility rate poses a serious threat to humanity. These two opposing trends (population growth and declining fertility) have been discussed from demographic perspectives, the implications for pensions and healthcare, as well as climate, migration, economic productivity and geopolitical power.
In general, these discussions lack the perspective of environmental sustainability. Population dynamics of different species is something ecologists have been studying for decades. Many species, including humans, tend to grow slowly and have few offspring for many years. Individuals of such species live longer and their populations rarely expand rapidly.
Species in this category generally live in a stable environment and their populations expand to a limit that their environment can support. If they temporarily use more resources than their environment can continue to provide, the population decreases until they are back in equilibrium with their environment.
Many native human populations only achieved equilibrium with their environment through trial and error, with population loss due to overharvesting of prey, for example.
Humans, elephants, giraffes, whales and many other species reflect this pattern of slow growth and stability.
There are other species that expand rapidly when their environment changes in some way that gives them an advantage. Insects, rabbits and mice are species with boom/bust cycles that reflect changes in their environment. Fires, floods, droughts, crop cycles and beech masts are examples of environmental changes that lead to these dramatic changes in population levels.
The pattern that human population dynamics follow depends on fairly stable environments. Therefore, the human population was generally stable or grew very slowly over millennia.
But the human environment didn’t change dramatically until a few generations ago when we started using fossil fuels in earnest.
Fossil fuels provided humanity with an unprecedented pulse of energy that enabled the creation of our modern world civilization (figure 1).
This unique energy pulse not only enabled the development of complex human societies, but also dramatically increased the human population (Figure 2).
Ecology tells us that successful species are those that live within the carrying capacity of their environment.
This is the ability of the environment to both provide essential resources and absorb waste for a given population.
This is a visualization of OurWorldinData.org. License under CC BY SA by the author Max Roser
For a given carrying capacity, there must be a balance between population numbers and consumption per capita, or transit. As a population expands, per capita throughput must decrease in order for the species to remain ecologically sustainable at carrying capacity. Alternatively, the population must decrease in order to rebalance with the environment. Not tragic for insects. Not so nice for humans.
The human species is no exception to this basic ecological dynamic. Our widespread use of fossil fuels has enabled unprecedented and unusual expansions in both per capita and population consumption. These dual, simultaneous expansions are currently pushing us beyond our carrying capacity into what ecologists call “overshoot.” Overshoot is the boom portion of the boom/bust cycle.
Unfortunately, the empirical evidence points to it humanity is currently in significant ecological overshootabout twice our carrying capacity (Figure 3).
On an annual basis, we currently use nearly twice as much natural resources as natural systems can produce, and create more waste than nature can safely absorb. This is possible because of the large amount of renewable resources that nature has accumulated over the millennia and organized into functioning ecosystems.
But overconsumption of these stored resources, or natural capital, is like eating our savings instead of living off interest. At some level, capital is reduced to the point where annual interest is minimal and insufficient to sustain us. If that happens, we will eat up the capital, which will then decline all the faster.
By reducing natural systems, we reduce the abundance that we can use in the future. At the same time, we are also disrupting many of the services these natural systems provide to humans and other species (such as climate stability, biodiversity richness, and nature’s ability to safely absorb our waste). The magnitude of our disruption to the biosphere threatens to collapse.
So what does all this ecology have to do with the human population reaching 8 billion?
The ecological perspective tells us that our growing per capita consumption of natural resources, coupled with a growing population that consumes, puts us on a collapse trajectory. It is this combination that puts too much strain on natural systems, resulting in many of the biggest challenges we face today: climate change, biodiversity loss and widespread pollution.
Urgent calls to reverse this situation to be made from many sources.
The dilemma we face is that we seem unwilling to reduce our per capita consumption, or our population size, to get back to carrying capacity. In reality, large reductions in both consumption and population are probably needed given how much we already exceed carrying capacity.
The current rate of declining fertility alone will not reach sustainable consumption levels fast enough because our ecological overrun is so great and rapidly deteriorating. Gradualism does not get us where we need to be. Government programs to increase birth rates, the global challenge is getting worse.
There are many initiatives to reduce our carbon footprint by developing ‘clean technologies’, such as renewable energy devices and the development of a circular economy. While these initiatives can make a contribution, the magnitude of change needed is far greater than what they are likely to achieve.
This leaves us with the problem of population. A wide range of religious, national, feminist, patriarchal, racial, political and economic sensitivities make dialogue about population levels difficult. Nevertheless, population size is a major issue (along with per capita consumption) in relation to many of the existential threats we now face. Understanding the role of population size can inform policies and actions to address these very real threats.
An important fact regarding the population is that about half of all pregnancies worldwide are unintentionally, and much more than half of these end in abortion. This means that at least a quarter of all pregnancies worldwide are both unintended and unwanted.
Naturally, there are large regional differences in these figures, with very different implications for regional carrying capacity. A further complication is the large differences in consumption per capita between regions.
Giving more women, especially young women, the means to control their fertility would be one way to lessen the negative impact of overeating we are now experiencing. Education in general, and especially education for women about reproductive rights, along with the availability of appropriate contraception, are proven means of increasing fertility self-control.
Education about population dynamics would also be important so that people can make informed decisions about their fertility.
The evidence regarding unintended and unwanted pregnancies indicates that much more can be done to increase women’s control over their own bodies. Policies and programs that support greater freedom of choice for women do proven their effectivenessbut needs to be spread more widely.
And of course, ensuring that basic needs are met also leads to voluntary reductions in the birth rate.
Managing their own fertility is important for women in both developed and developing countries, from an ecologically transcendent perspective. Developed countries have higher levels of consumption, so fewer births globally make a greater contribution to reducing the overshoot. This allows necessary consumption in poor countries to increase without exacerbating the overrun.
In developing countries with lower levels of consumption, fewer unintended and unwanted births means that consumption per capita can increase more if fewer people consume.
The production capacities of ecosystems, along with their ability to absorb waste, are relatively fixed in terms of what they can sustainably deliver each year. So it’s a matter of balancing consumption and population to make sure we operate within carrying capacity.
There are several ways to achieve this balance, but we are not currently paying much attention to carrying capacity, or what affects it – consumption and population. This is one of those important but difficult conversations we need to have with each other, both within and between countries.
It is unlikely that we can satisfactorily address any of the existential environmental or social threats we face until we do.