12.5: The Human Footprint - Population

Virtually everyone who has looked into the matter agrees that the two ‘ultimate drivers’ of our global ecological crises are continuing human population growth—which most people don’t want to talk about—and continuing economic growth, leading to out-of-control consumption of ‘resources’—which pretty much nobody wants to give up. The human footprint, our species’ overall ecological impact, classically has been formulated as I = PAT, where P represents the size of the human population, A stands for affluence, a measure of our average per capita consumption of resources, and T is the technology factor, able to increase or reduce the product of the other two factors—the primary drivers—somewhat (see Ehrlich and Holdren, 1971 for the classic paper). These two drivers, population and consumption, and the “economic growth” that fuels the latter, need to be considered in more detail in order to get a grasp of what’s actually happening in the “war” we are currently waging against nature.

The Human Footprint: Population

To have an intelligent conversation about population, the first thing everybody needs to understand is the mathematics of exponential growth; our collective inability to understand this has been called “the greatest shortcoming of the human race” by renowned physics teacher Albert Bartlett (Bartlett, 1969; also see Bartlett, 1978, especially parts 2-4). ^[14] It’s the basic way to describe the growth of biological populations when not subjected to negative feedback, but the mathematics applies to anything growing steadily at a constant rate, represented as a percentage of the total, per unit of time—including, in the abstract world, money growing at a certain rate of interest, as will be considered in Section 12.7. The relationship between the rate of growth–the added numbers over a given period of time described as a fraction of the total number in the population at the beginning of that interval—and the time it takes for the population to double in size—the ‘doubling time’—can be worked out mathematically in terms of the natural logarithm of 2, but it can be approximated as doubling time = 70/growth rate in percent. Thus, if a population is growing at five percent per year, then its doubling time will be 70 divided by five or 14 years. The important thing about exponential growth, however, is that it can kind of sneak up on you. If you try to graph the growth over time, you don’t get a straight line, as you would if the relationship were linear, you get what some call a ‘J-curve,’ a line like a recumbent ‘J’ that curves upward, appearing to shoot off into space as the exponential function approaches infinity. The reason it does this, of course, is that, for every new interval of time, the base which will be multiplied by the percent growth rate is a little larger than it was before, so the number that will be added over the next interval will be larger, and so on and so on.

An example often used to illustrate the ‘sneakiness’ of this kind of growth is the case of an exotic waterweed growing on a pond; the waterweed has a doubling time of one day and is capable of covering the entire pond within 30 days. For the first three weeks after it is introduced, the floating pondweed is barely noticeable, and it hardly attracts attention even after four weeks have gone by; the people living along the shoreline aren’t too concerned about it, saying they will only do something when it covers half of the pond’s surface. On what day will that be? The answer, of course, is on the 29^thday—once a ‘base’ of reproducing plants has built up, the takeover occurs very quickly, catching the locals by surprise. A similar but more telling example is a bacterial sample inoculated onto the nutrient medium in a sterile petri dish. When the plate is incubated at a favorable temperature, the number of bacterial cells follows a typical J-curve, their population slowly growing from a tiny speck into visible circular colonies that spread across the agar, enjoying luxurious growth amid a seemingly infinite amount of nutrients, free from predators, competitors, and pathogens. Over time, however, nutrients run thin while harmful metabolic wastes build up; with no other kinds of organisms present to recycle wastes back into nutrients, bacterial growth stalls, and then the number of living bacterial cells drops rather precipitously as the colony reaches the finite limits of the plate.

The example has been used to illustrate the risk we humans run as we proceed to take over the surface of the Earth, simplifying ecosystems by eliminating more and more of the ‘other’ kinds of organisms whose ecological roles include breaking down our wastes and producing nutrients we can use, even as our numbers continue to climb. The standard reply of uncritical optimists has been that this won’t be a problem because ‘we humans are a lot smarter than bacteria,’ but unfortunately this is yet to be demonstrated at the global level. In the big picture, our species’ growth certainly looks as if it followed a J-curve. Our numbers stood at under one billion throughout all of our evolutionary history up until around 1800 or so, when they started to turn upward as the Industrial Revolution got underway; they then shot up steeply after 1950 ^[15] in what is known as the “Great Acceleration,” as discussed in section 12.1. Our global population was reportedly 7.6 billion in mid-2018, and it had an overall rate of natural increase of 1.2 % per year (Population Reference Bureau, 2018)—which, by the straight math, would give a doubling time of around 58 years, yielding a total of over 15 billion people on the planet by the last quarter of the 21^st century. When projections are made, however, our overall growth rate is generally assumed to be falling, and since its highs during the 1950s and 60s–which resulted in a doubling of the total from three billion in 1960 to over six billion in 2000—it has been falling in many places around the world, but not everywhere. An overall increase of 28% is expected by 2050, adding around 2.2 billion for a total of 9.8 billion (PRB, 2019); a different projection yielded 11.2 billion for 2100 (UNDESA, 2017). Given our human capacity for exercising choice over what we do—a capacity that’s frequently overlooked in these modeling studies—the number we will actually add is up for grabs; what will not be up for grabs, however, is the fact that each additional human will come with certain needs and ‘demands,’ and that the cumulative impact of these will largely determine the state of the Biosphere in 2050, in 2100, or any other future time.

One important concept to keep in mind when considering human population growth is the demographic transition—the change a society makes, with the help of modern sanitation, vaccination, and other public-health-related procedures, when it goes from having a high birth rate and a high death rate to having a low death rate and subsequently a low birth rate, a changeover that many presently industrialized countries made early in the 20th century. A second important concept is what is known as demographic momentum, the fact that the growth rate of a population at any given time will reflect its current age structure, such that populations having a large percentage of young people will continue to grow in size for many years even if the average number of children born per woman (the total fertility rate or TFR) lowers to replacement level, as this large cohort enters reproductive age, begins contributing to the population, and then lives alongside its children and grandchildren.

Brazil, for example, like much of Latin America, underwent a demographic transition between the mid-1960s and the mid-1990s, with its total fertility rate falling from an average of 5.4 children born per woman in the late 1960s to an average of 1.9 by 2010, below replacement level. Its population is continuing to grow, however, because of the large number of children born during the high-growth years, who are reproducing now and will be continuing to bear children for some time to come; if current rates continue, the population of the Amazon region is thus expected to double in less than 30 years (Williams, 2011). Sub-Saharan Africa, however, is said to be “the youngest region in the world” (Madsen, 2013), and the demographic transition is said to have “stalled” in many of its countries; with 46% of Middle Africa’s population under 15 years of age (PRB, 2019), there is enormous demographic momentum built into it. In 2018 this part of the world had a total population of slightly over one billion, an overall average rate of increase of 2.7% per year, and the highest TFRs in the world, with Nigeria (already maintaining a population base of over 400 million) averaging 5.5 children per woman: Mali 6.0, Angola 6.2, the Democratic Republic of Congo 6.3, Chad 6.4 and Niger an astonishing 7.2 (Population Data Sheet, 2018)—a figure that came down to seven by 2019; increases of one to two billion people are expected by 2050 in the Democratic Republic of the Congo and Nigeria alone (PRB, 2019). Contraceptive use among married women is very low in these countries, partly from lack of knowledge and/or availability, but also preference or cultural expectation; in Chad and Niger, married women reportedly will state that an ideal family size can include up to nine children (Madsen, 2013).

A reason often given for desiring such a large family size is to ensure that some children will be able to provide care for parents as they age, but the extent to which this now proves true is questionable, as increasing populations are less and less able to support themselves within deteriorating ecosystems and many young people are forced to migrate to urban centers. In Madagascar, even though the population growth rate has fallen from 2.9%, with a TFR of 4.6 children per woman, in 2013 to 2.6% and 4.1 in 2018, people are leaving the overpopulated interior of the island and migrating to the coasts; there, however, they are finding that “the number of people who are going out to catch fish to feed their families is going up exponentially, and those fishermen are having to work harder and harder to catch smaller fish that are farther and farther down the food web,” according to Dr. Vic Mohan (Williams et al., 2012). ^[16] As has been pointed out by many, to slow this growth and eventually stabilize the human population, advances in women’s and children’s rights, improving the position of women in society, and securing for them a basic education and access to contraception and family planning services are needed worldwide. Education for women is considered the key, since the number of children a woman will have has been shown generally to vary inversely with the number of years of education she has attained. Moreover, if unintended pregnancies—those not planned or unwanted–could be minimized around the world, the overall fertility rate would decline substantially. A little-known statistic that is somewhat shocking in its significance is that the percentage of unintended pregnancies is highest in North America, Latin America and the Caribbean–where they may make up more than 50% of all pregnancies (Crist et al., 2017).

Human population growth in or around most any relatively ‘natural’ area usually results in decreasing biodiversity, but continuing population growth is particularly problematic for the biodiversity ‘hotspots’ around the world, regions identified as conservation priorities for having both very high concentrations of species diversity, with many species found nowhere else in the world, and also very high levels of habitat fragmentation and extinction threat, threats that are often related to high human population densities. ^[17] It is also a concern for the three major tropical wilderness areas (TWAs)—the Amazon Basin, the Congo Basin, and New Guinea and its associated archipelago—high biodiversity areas that just a few decades ago were mostly intact, with relatively low human population densities (usually less than 5 people per square kilometer), and that were expected to be “storehouses of biodiversity” that could serve as “controls” for the hotspots, as well as places where indigenous peoples are said to “have any hope of maintaining their traditional lifestyles” (Mittermeier et al. 1998, 2008). ^[18] By 2010, the hotspots were estimated to contain almost 1.5 billion people, with an average density of 99 per square kilometer, while the average population density in the TWAs had increased to 13 per sq km; their population growth rates, moreover, were averaging three percent per year, more than twice the rate in the hotspots–all worrisome numbers, given that “the livelihood and resource demands for most of those people likely came from within the respective hotspots or TWAs” (Williams, 2011). ^[19]

The famous I=PAT Equation, referred to earlier, is a thumbnail sketch of how the size of the human population can be related to its environmental impact: basically, the impact is the product of the number of human beings multiplied by the average amount each person in a given society “consumes” from the (local and global) environment, adjusted by whatever technologies enable them to consume this much. The relationship is somewhat intuitive, and the expression was not meant to be quantitative, but rather to convey an overall qualitative relationship that seems pretty hard to deny (although some may try). Lest it be taken too literally, however, to mean that impact simply increases linearly as population increases, John Harte (2007) details a number of ways in which the relationship can be dynamic and nonlinear. Consider, for example, the effect of a temperature rise above 80 ^°F in a well-off community, triggering the use of air conditioning, thus increasing electricity usage and fossil fuel consumption and setting off a positive feedback hastening yet more planetary warming, an effect that will grow in proportion to population size. Or consider the highways and other infrastructural connections between three cities—aspects of the built environment that may make life easier for people but much more difficult for wildlife, directly causing mortality, cutting up blocks of habitat and interfering with migration patterns and breeding opportunities for many species; with just three cities, three roads can connect them, but as the population grows, the original three cities will increase in size while three new ones may spring up, necessitating twelve or more interconnections, severely fragmenting the terrain and possibly eliminating the larger-bodied and more sensitive species. Moreover, “rising numbers impede governance and problem-solving,” Harte cautions, so we may find ourselves in “an intensifying downward spiral.” So far, people in many places have accepted these “shifting baselines” and been able to adjust, but the cumulative effects are likely to be catching up with us as we approach 2050.

Attempts have been made to quantify various aspects of the relationship between human population growth and climate change. At the individual level, Paul Murtaugh and Michael Schlax (2009) calculated that one extra child born to a woman in the United States increases her ‘carbon legacy’ into the future by an additional 9,441 tonnes of \(\ce{CO2}\), 5.7 times her own contribution; Seth Wynes and Kimberly Nicholas (2017) used their calculations to conclude that having one fewer child would have far and away the greatest impact, coming in ahead of living car-free, avoiding air travel and eating a plant-based diet, which also made their list of top recommended actions. In a macro-level study with serious implications for future global trends, Michael Raupach and colleagues (2007) utilized a formula in some ways similar to the IPAT equation to separate out global and regional drivers of the growth in \(\ce{CO2}\) emissions from 1980 through 2004; their report’s Figure 5 is especially telling. It is noted that the “developing and least developed” regions of the globe, inhabited by 80% of the world’s population, accounted for only 23% of global cumulative emissions, but were responsible for 41% of emissions in 2004, and accounted for 73% of global emissions growth; they state “Fig. 5 has implications for long-term global equity and for burden sharing in global responses to climate change,” letting their readers draw any further conclusions.

A number of modeling studies have utilized the general form of the IPAT relationship with the addition of some social and economic indices to make projections of future carbon emissions ^[20]; of particular interest here is study by Noah Scovronick and colleagues (2017) utilizing an updated version of “a leading cost-benefit climate-economy model (CEM)”—the same basic kind of modeling done by the IPCC ^[21] in its “integrated assessment models” (IAMs), which will be considered in more detail in section 12.7—to examine how “cost-sensitive” mitigation decisions will be affected by the size of the human population and also by what they call “population ethics.” Under the latter heading they explore how “two approaches to valuing population,” total utilitarianism (TU) and average utilitarianism (AU), can lead to considerably different outcomes. As this thinking goes, an ‘average’ utilitarian, such as John Stuart Mill, takes as the ethical aim maximizing the average happiness (termed utility) of a given group of people, while a “total” utilitarian, supposedly following the thinking of Jeremy Bentham, seeks “the greatest good for the greatest number,” understood as getting the total amount of “utility” to be the greatest it can possibly be, overall. As interpreted today, this may mean maximizing the total number of people, even at the expense of their average happiness. Since attaining this goal may result in a very large population composed of people whose individual life experience may be only very slightly positive, the upshot of this line of thinking has been termed “The Repugnant Conclusion” ^[22] (see Parfit 1984). Scovronick et al. just happen to note that all of the leading climate-economy models that try to optimize for costs share a total utilitarian (TU) social welfare function rather than an average utilitarian (AU) one, revealing an important aspect of why much of the prevailing thinking in “global governance” circles today is unable to slow our progression into worsening climate change.

The fact that these and other studies of the relationship between human population growth and carbon emissions are being done at all, however, makes the absence of recognition of the importance of population size all the more glaring in recent IPCC reports and most international environmental discourse. Moreover, if utilitarian, and especially TU-type thinking, is already built into the assumptions of the modeling programmes, then just what is being valued, and how, should not only be made explicit but should be open to public input and academic debate. None of this appears to be happening, however; it seems, that the topic of our ever-increasing population has become one of those “elephants in the room” of which Eviatar Zerubavel speaks, as discussed in Chapter 11. Martha Campbell explores some of the factors leading to this peculiar situation in “Why the Silence on Population?” (2007). As she explains, rapid population growth and some of its accompanying problems garnered world attention in the 1960s and 70s, and the adoption of “family planning” measures–providing information about and access to modern contraception methods that had recently become available—began to show success in reducing population growth rates in many places. By the 1990s, however, an active avoidance of the issue had appeared in many academic and policy circles, apparently including some quite central to setting the international agenda for our trajectory into the Anthropocene.

Campbell identifies six contributory factors creating a “perfect storm” shoving the issue off the table by the early 2000s. Birth rates had come down in many places, while consumption in the industrialized countries had grown enormously, clearly outpacing that of the less developed regions even though their populations were growing more slowly; meanwhile, family planning funds were being diverted into the fight against HIV/AIDS, and conservative pro-natalist groups were becoming more influential, while the academic community was in the grip of a theory holding that some external factor was needed to make couples opt for smaller families. But the sixth and perhaps most effective factor in silencing serious discussion of the need to limit our population growth was a matter of social psychology; a certain way of thinking came to be roped off from acceptable discourse, inside and outside of academic and policymaking circles, by means of the taboo-ification of certain terms and even the creation of particular epithets to be hurled at violators of the prohibition. Northern consumption patterns were placed in the crosshairs as a substitute target “at Cairo,” the UN’s 4^th International Conference on Population and Development (ICPD) held in Cairo, Egypt, in 1994—not undeservedly, but this was followed by an effort to paint all family planning efforts with the broad brush of coercion, despite the fact that, as Campbell claims (2007), “the vast majority of family planning programmes were designed to make family planning easier for women and men to obtain, not to force them to control their fertility.” The new term reproductive health was introduced to supersede the term family planning, but it also served to make the latter politically incorrect, often along with the word ‘population’ itself, and people who still employed the older vocabulary were saddled with derogatory adjectives like ‘neo-Malthusian’; with adoption of the position that “macro-level data was conducive to inhumane approaches in reducing birth rates,” she claims, it became unacceptable to consider issues from this big-picture perspective at all (Campbell & Bedford, 2009).

Unfortunately, it seems that much of this enforced silence on population issues is still around today. Calling out the mass psychology propping up “The Last Taboo,” however, Julia Whitty (2010), a woman of Indian heritage, expresses concerns about India’s increasing desertification and declining crop yields and maintains that “the root cause of India’s dwindling resources and escalating pollution is the same: the continued exponential growth of humankind.” As she explains, in 2010 India had 1.17 billion people—17% of humanity–trying to live on less than 2.5% of the Earth’s land, and was facing an additional growth of “400 million to 2 billion” by 2050. Unafraid to take on the macro-level issues, she illustrates her article with the dramatic J-curve of our global population growth and our surging ecological footprint, and she observes that, while human rights activists found the conservationists’ take of “people vs nature” to be “simplistic and even racist” in failing to address problems of poverty and injustice, she notes that these activists “in turn have tended to deny the limits of growth,” which Whitty refuses to overlook. She recounts the stages of the “demographic transition”—the first a state of high birth rate offset by high death rate, the second a stage of rapid population growth as the death rate falls below the birth rate, and the third a state of low birthrate back in balance with the lowered death rate, often linked with women’s education and economic improvement; she then points to the lamentable literacy rate of women in India—only 54% in 2010—and makes the prediction that “whether we are a world of 8, 9.1, or 10.5 billion people in 2050 will be decided in no small part by the number of illiterate women on Earth.” The fourth stage in the demographic transition, she continues, is a “stable and aging population,” but she notes a recent study identifying a fifth stage, a reversal of the long-established relationship between economic development and reduced fertility (see Myrskyla et al., 2009), which, she remarks, is “good news for those who worry about Social Security deficits, but bad news for those who worry about societal security on a planet with finite resources.” Whitty dares to ask, “how much has our silence around population growth contributed to the emergence of this fifth demographic stage?”—and she says she’s looking forward to “the sixth stage in our demographic maturity: the transition from 20^th-century family planning to 21^st-century civilizational planning.”

There is, however, one final point to be considered under the population issue, one that, from the perspective of this point in time, seems so glaring that one must wonder if it lies at the heart of the ‘elephant in the room,’ denial that there could be a ‘population problem.’ With the blossoming of truly amazing scientific knowledge about almost everything, an obvious moral buffer between us and the absolute limits of the Earth is emerging into view, given that questions about population size are ultimately value questions. The silence surrounding it is even louder and heavier than that surrounding the p-word itself, since at those rare times when human population growth does make it to center stage it is usually framed, as pointed out by Eileen Crist (2012), in terms of the question “how many people can the Earth support?”—the assumption being, of course, that supporting people is the only purpose the Earth is meant to serve; what else might there be?

Such silencing phenomena are often efforts to maintain collective denial over a shared sense of moral culpability, as discussed in Chapter 11. Yes, there may be evolutionarily-instilled factors that also militate against open recognition of the need to limit population growth of one’s own “group,” however defined; in addition to the natural desire of many people to have children, bigger groups can defend themselves, and have generally been able to get away with bullying smaller ones, going way back. But our collective silence on the population issue may mask an even greater desire to avoid confronting the reality of what our burgeoning numbers inescapably mean on the ground: that there is less and less room for nonhuman life, that many of the ongoing ways in which we displace nonhumans are filled with brutality and suffering, and that nonhuman lives are filled with inner subjective experience—and therefore are often filled with terror and loss, as we perpetrate an “Animal Armageddon” across the planet. What else might there be for the Earth to support, besides more people? The myriad other living beings that those additional people will squeeze right out of existence, that’s what. Can we see them now?

Eileen Crist insists that we see them, as well as the socially-reinforced silencing that surrounds it, noting “The ongoing and escalating genocide of nonhumans is shrouded in silence, a silence signifying disregard for the vanquished. [. .] Silence is how power disdains to talk about their extinction.” (Crist, 2012, p. 142). She believes the term anthropocentrism is much “too feeble and academic” to describe what has given rise to this genocidal project, describing it as “the open or tacit stance of human supremacy, ” a stance that “manifests most clearly in the attitude of total entitlement”—an entitlement “that can hardly be challenged because it claims both consensual power and morality on its side (Crist, 2012). And perhaps this entitlement is nowhere more evident than in the exhortations against abortion, wherein the life of a single-celled embryo—because it is a human embryo (and despite the fact that, during development, its fundamental relatedness to all other animal life on the planet can be seen very clearly ^[23])—is presumed to be of inestimable value, while all the nonhuman lives that will be displaced by its being brought fully into the world are counted for nothing, and are deemed not even worthy of mention. It is only with the arrogance of such entitlement that pronatalists can profess to be ‘pro-life’—as if the only ‘life’ that has a value is so obviously human life that the word needs no qualification.

We still have a choice, Crist maintains, between “Resource Earth” and “Abundant Earth,” the former with a human population of many billions and little else, the latter with a declining human population that is able to make room for rebounding numbers of wild nonhumans in all their diversity and complexity. All it would take to set us on the path to Abundant Earth is more and more women choosing to limit their childbearing—“an elegant solution—and not an authoritarian one, because in a global human society actually awakened to the precipice of Life’s collapse, many women and men may well choose none, while others choose one, and a few choose two” (Crist, 2012). On the second path, by 2100 we could be on the way to a human population eventually leveling off around two billion, in the ballpark of what has been estimated would be the “optimum human population size,” where there would be enough for all life to flourish (see Daily et al., 1994). One thing is clear—we need to start talking about population again, and all its consequences that we’ve been denying. It’s time to change the conversation.