New book argues for a sustainable world with 3 billion people

In his new book A Planet of 3 Billion, Christopher Tucker presents a vision of a future world inhabited by 3 billion people, compared to 7.8 billion today. Inspired by Joel Cohen’s 1995 book How Many People Can the Earth Support? Tucker sets out to answer exactly this question. The ecological destruction caused by humanity demands reduced consumption and a new economy, but also strong future population decline. To understand why and how this can be achieved, Tucker uses a geographical approach. Despite a few weak sections, this book is worth reading by both scholars and general readers.

By Frank Götmark

Anyone who has realized that the human population is too large would probably be interested in a book titled A Planet of 3 Billion: Mapping Humanity’s Long History of Ecological Destruction and Finding Our Way to a Resilient Future. A Global Citizen’s Guide to Saving the Planet (2019, Atlas Observatory Press, 324 pp). As Chairman of the American Geographical Society, Christopher Tucker explores questions of population and sustainability from a scientific foundation.

Chapter 1 begins with “I am an unrepentant capitalist”. In addition, Tucker states that technology should be an important future force in a world changing for the better. However, he also states that economic “growth-mania” is leading us astray, and that national economies must be revised. The book is written to make concerned citizens think about the problems caused by both increasing population and consumption, and about possible solutions.


Chapters 2-5 give a good overview of environmental and ecological problems that humanity caused historically, and how they accelerated during the last 60-70 years. Tucker introduces, and emphasizes throughout the book, the importance of geographical analysis and thinking. We need to map how and where problems arose, and analyze present and future conditions geographically, to be better prepared to solve problems (as part of this effort, Tucker encourages the use of, a free and interactive geographical Internet site – at the moment not available, being relocated).

Chapter 3 (“Earth’s People Problem”) introduces the idea of Homo sapiens as an invasive species, a concept used by conservation biologists for animals and plants invading and negatively affecting ecosystems. One point should have been added, namely that on the continent where humans evolved (Africa) people did not cause the extinction of the megafauna (large predators like lion, large herbivores like hippo and elephant), as happened elsewhere as humans spread. No doubt people influenced the African ecosystems, but over time humans co-evolved with the large mammals. In contrast, as we entered other regions at later stages of our development, species extinctions followed in our footsteps (including many huge mega-herbivores, unaware of human hunters, and more than 1,000 flightless bird species on islands). We have been even more invasive in colonized regions than the non-human invasive species, many of which came along with us (e.g. rats, domestic cats, and many plants).

Tucker discusses E. O. Wilson’s Half-Earth-project (“protect 50%”) which he likes but considers too vague, and in need of geographical analysis. Later on, he introduces the concept of global ecoregions and emphasizes their value for classification and protection of regions and habitat types. Implicit is the concept that biodiversity is best protected in natural and semi-natural ecosystems, as an approach focused on protecting individual species will not lead to effective nature conservation. Even in my relatively small home country (Sweden) there are at least 65 000 wild species. True, certain species, such as indicator and keystone species, deserve special attention. But protecting geographical ecosystems and habitats has long been the cornerstone of nature conservation. Sadly, there is a strong bias in ecosystem protection toward land of low economic value to humans. It would have been valuable here to introduce “systematic conservation planning”, important work done by Chris Margules, Bob Pressey and colleagues, and its geographical components.

Chapter 4 describes early human history, industrialization of the global landscape and urbanization, with many interesting (but depressing) details. Then follows an excellent chapter on the geography of humanity’s waste (even more depressing): we learn about greenhouse gases, 400 ocean dead zones alongside our continents (most of them still growing), heavy metals, endocrine disruptors, radioactive materials, noise pollution, and the flows of our garbage, such as those forming five continent-size plastic garbage gyres on the oceans. Tucker finds some hope in urbanization, if carefully planned, since alternatives other than continued urbanization may be worse. But it’s important to note that conventional urbanization is an important contributor to our environmental problems. For example, urbanization, combined with increasing global trade, is an important factor causing tropical deforestation, as shown by Defries and colleagues.

Chapter 6 describes conservation and protection of ecosystems, and chapter 7 considers “Connectography as Possibility and Peril”. Those who follow the ALERT Conservation newsletter know about the perils of building large road systems in the last remaining wild areas. Such infrastructure development is accelerating in the developing world, abetted by investments from developed countries and especially China. But Tucker also sees opportunities for ecologically sustainable development, in a vision of connected, sustainably engineered cities.

In chapter 8 Tucker discusses Earth’s maximum carrying capacity. He relates to the world in 1950, with about 3 billion people, and refers to markedly increasing ecological debt since then. Comparing 2010 with 2030, a projection (see Figure below) suggests the rich and middle class will have grown by 1.7 billion people, and the poor and vulnerable will decrease by 1.05 billion. Such growth will likely increase current ecological debts considerably. But will the projection come true? Tucker concludes, “I have no doubt that capitalism could generate enough food and water to keep 9 billion or 11 billion people served well above their minimum… requirements”. But the dramatic negative consequences of this scenario are clearly presented in his book.

World population in 2010 (light color) and projection and change to 2030 (darker)

A discussion of energy leads to the statement that “Energy is not the limitation”. Tucker presents the nine planetary boundaries, and notes that this approach fails to engage directly with the environmental costs of large and growing human populations. He also presents the ecological footprint approach, discussing it in detail and stating in passing that it is “not intended to determine how many people Earth can support”.

Tucker does not calculate human population size at maximum carrying capacity. He focuses instead on something closer to an optimum outcome, enabling high human wellbeing to coexist with healthy, diverse ecosystems. He imagines this could be achieved with “perhaps as many as 3 billion people inhabiting the Earth” – if we improve efficiency of resource use, deal with persistent wastes and radically rewild much of the planet. Interestingly, Tucker’s estimate of 3 billion people is supported by a recent study by Lianos & Pseiridis, who concluded that 3.1 billion would be sustainable while able to provide for an average European standard of living.

Much discussion in the book refers to the global population in general, often referencing “we” and “humanity”. But nations are important in geography, and in chapter 8 they are mentioned as “sovereign entities” (as they are also characterized in many UN documents). In my view, nations are what matter the most in practice – in setting population policies, dealing with environmental problems, political issues, and more. I would have liked to see nations better integrated with geography from the start (although they are also discussed later on in the book).

Chapter 9, “How to bring the population down to 3 billion” should be central to the book, and of interest to TOP readers, but it is short (only 10 pages). Tucker makes clear that we need a “campaign for global women’s empowerment, women’s education, women’s workforce integration, and women’s access to family planning technologies”. This is important and good, and such a campaign should be started. I also welcome Tucker’s emphasis on declining populations (Japan, South Korea, Europe) being “embraced as models”. Unfortunately, people in these countries mostly do not yet realize the value of decreasing population. For Japan, the concept of depopulation dividend has been suggested.

Neither in chapter 9 or elsewhere does Tucker discuss large-scale immigration into the USA, Australia, Sweden, and other European countries. This seems like a serious oversight, given immigration’s ability to negate low birth rates and drive continued unsustainable population growth in these countries. Tucker describes the critical role of fertility rate (TFR, total fertility rate) in population trends, but introduces “negative fertility” which is confusing. Presumably it means “below replacement” fertility leading to a “negative growth rate,” which in normal language is the same as population decline. He does not explain the important role of population momentum (population growth due to large young cohorts, even under low TFR). There is some mention of countries and forms of family planning, good. Population taboos and denial are not dealt with, other than a short reference to “barriers”. Tucker does not specify when he thinks a population of 3 billion people might be reached. Of course, this is a difficult question, but requires some mention.

Chapter 10 is about economic de-growth and ecological economics, a field which despite good intent has “its own blind spot” in often not dealing sufficiently with population size and growth (see also this recent paper). New concepts and economic goals are needed for an age of de-growth, according to Tucker; in addition, he discusses robots and technological opportunities. Geopolitical aspects of population decline follow (chapter 11), dealing with the USA, China, and other countries in some detail.

Chapter 12 is a “cookbook of solutions” for leaders and citizens, with ten “recipes”: a global campaign to empower women and promote family planning; sustainable, smart and resilient cities; geographically based restoration and rewilding strategies; identifying the primary forms of land use and their consequences; eliminating waste from supply chains; low-impact infrastructure; stop impeding and diverting natural flows of water; avoiding “growth language”; changing current “geo-engineering” paradigms; and developing alternatives to the land rights model of modern capitalism. Each of the ten points is explained and explored in some detail.

This is a broad and insightful menu, worth pondering. In my view, a point about communication with religious leaders should be added – important, to judge from a recent global study of fertility. Few journalists and educated people in the West are aware of the strong growth in religiosity around the world in recent decades, especially in Africa and western Asia. If the UN’s population projection is correct and current trends continue, the additional 3.1 billion people on the Earth in 2100 will be highly religious. Research in political demography deals with these aspects, and could have been discussed in chapter 11. Differential fertility and population growth among ethnic groups and nations occurred earlier in history, and seems likely to continue during this century. Once again, we see the importance of attending to nations and national policies in any geographically-informed approach to sustainability.

The bibliography contains about 195 references and footnotes, not directly linked to the text in all cases, but sometimes giving extra, interesting information. There is a section with 21 maps in color, and a few other graphs. The book ends with a warning about the consequences of ignoring reality, an epilogue, and three appendices, one with letters to the Pope, Jeff Bezos, Bill and Melinda Gates, and China’s president. Regarding the consequences of ignorance, Tucker concludes that “a world of 9 billion, 11 billion… is fast approaching. This will bring such widespread industrialization of the global landscape and such enormous volumes of persistent wastes that our terrestrial and marine ecosystems, as well as the atmosphere that they fundamentally shape, will become unrecognizable.”

Overall, the book can be commended for its focus on optimum human population rather than the miserable maximum implied in studies of Earth’s “carrying capacity” (such as those reviewed in Joel Cohen’s afore-mentioned book). Tucker’s geographic perspective gives a structure to the many stresses that human activity exerts on ecosystems. Unlike conceptual ideas such as “global footprint”, Tucker emphasizes that sustainability requires a focus on the size of future human populations, to be combined with changes in our economy, in all places where people live. There are too few books that present population as central to our environmental challenges. Christopher Tucker has made a valuable contribution in presenting a possible hopeful future, and in illuminating the pathways toward achieving it.


Solutions exist to rapid population growth and overpopulation. Learn more about them here!

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8 thoughts on “New book argues for a sustainable world with 3 billion people

  1. Thank you for this fine review. It was informative, and thoughtful. I suppose the first (and most important) point was that the book’s author is addressing the big problem. The silliness of claiming to be a capitalist will fade as the reality gets through. The “world structure” issue is the economic arrangement (largely corporate) which is continuing to cause, and hide, the overall population problem. Also, food production, as done now, cannot be sustained (as the author blandly claims).

    E. O. Wilson has acknowledged that overpopulation is the problem. His “Half Earth” is so unattainable that it’s plain foolish. To paraphrase: as Sherlock said …. when you remove the things proven false or unrelated to the matter at hand, what remains is the truth. The truth is: the only solution is to drop our world population, by having fewer births. This must be proclaimed.

    1. Yes indeed. And in the final analysis, that’s the most valuable thing about the book: it makes a convincing case that there is no path to sustainability without a drastic decrease in human numbers.

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