1 The question posed by this book – whether we should stop bringing children into the world to save the planet – raises a host of other questions. The first is the true role of world population growth in today’s ecological crisis. To what extent is the ‘population factor’ (in purely numerical terms) contributing to environmental degradation? And a corollary question: if the population stops growing, or even begins to shrink, will that mean the planet has been saved? But other questions also arise: have decreasing birth rates had different effects on the environment in different parts of the world, given socio-economic inequalities? If, for example, global fertility falls below the level of generational replacement, will there also be a large fall in carbon dioxide emissions, given differences between countries in emissions per capita? If action is needed to accelerate the demographic transition where it seems to have stalled (in certain African countries, for example), who has the right to make the relevant decisions? The international community? And what conditions are required for population policies to be effective? What real legitimacy do they have? Should the freedom to reproduce be maintained at all costs, or, on the contrary, can it be sacrificed in the name of the collective interest?
2 One of the merits of Emmanuel Pont’s book-length essay is its examination of what is commonly referred to as ‘the world population problem’ not only from demographic and ecological, but also economic, political and ethical perspectives. It is similar in spirit to Matthew Connelly’s Fatal Misconception: The Struggle to Control World Population, which considers a variety of logics and forms of reasoning.
3 Writing in a polished, lively style, Pont introduces the demographic question in a classical and instructive way. He presents the broad outlines of the history of the world population, with self-contained sections to define key concepts (demographic transition, demographic inertia, Malthusian trap, dependency ratio, etc.).
4 The second part of the book deals with the relationship between the environment and population as such. One chapter is devoted to responsibility for greenhouse gas emissions. The emphasis here is on carbon dioxide emissions linked to the use of fossil fuels (oil, gas and coal) and deforestation. Since ‘carbon neutrality’ (emissions not exceeding the absorption capacities of natural and artificial carbon sinks) is a particularly demanding objective, it is important to identify who is ‘responsible’ for these emissions. For example, while China is the largest producer of carbon dioxide within its borders, it is the United States that emits the most carbon dioxide per capita. Another approach is to ask what economic sector is responsible for the most emissions. Industry sits at the top of the list (at about a third of total emissions), followed by agriculture and deforestation (each representing a fifth). But who, in the end, pollutes the most? Is it the consumer, the worker, the citizen, the decision-maker, the investor, the economic and social system more generally? Given that countries with high birth rates contribute very little to total emissions, can we really hold the world population, which lives largely in the Global South, responsible for the ecological crisis? On the other hand, since poor countries want to and must develop, is it imaginable for carbon dioxide emissions not to increase?
5 The ecological crisis goes beyond climate change. Pont delves into the various dimensions of the environmental question based on nine ‘subsystems’ of the Earth identified in a 2009 study: climate, biodiversity, nutrient cycles, land use, freshwater use, ocean acidification, the ozone layer, aerosols and chemical pollution. Among these subsystems, the first four have doubtless already passed the corresponding ‘planetary boundaries’.
6 With particular attention to argumentative rigour, Pont looks critically at the diversity of data on the relationship between population and environment that has been cited in the scientific literature or taken up in the media. He scrutinizes the IPAT equation  and highlights the well-known limitations of analyses that are either static (i.e. that do not consider how interdependencies can play out and shift over time) or globalizing (i.e. that neglect the heterogeneity of populations).
7 One particularly interesting part is a discussion that combines elements of environmental ethics (‘potential trade-offs seen from a normative point of view’) and population ethics (‘how to compare the interests of different persons, or the value of existing rather than not existing’). He then turns to ecological compromise: ‘Can the effects of measures on the population and on the environment be compared for the ecological crisis as a whole?’ Taking the example of water, he shows how difficult it can be to quantify the effective pressures on a resource. How should we assess water scarcity, especially since it is so unevenly ‘dispersed’ across the Earth’s surface? Similarly, quantifying biodiversity, or its loss over time, is a very complex challenge.
8 Next comes a reflection on political compromise. Here, Pont looks at questions of power and the organization of society. What should we think, for example, of outside interference in the affairs of different societies on ecological grounds? To what extent is it legitimate to encourage (force?) countries to limit their birth rate in order to protect their own environment? International governance on ecological issues (on the model of the COP for the climate) runs up against the sometimes conflicting interests of different countries. Pont writes of how ‘extractivism’ reflects the international balance of power, as ‘the resources of poor countries are exploited by the richest while waste and pollution move in the opposite direction’.
9 In the book’s final section, Pont considers the decision of whether or not to have a child as a confrontation between individual choice and the general interest. He returns here to the question of responsibility: ‘If having a child is a heavy burden on the environment, or if the child risks having a horrible life, then these are indeed valid reasons to question individual right’, he notes. Here, too, the numerical data advanced by some authors, such as the estimated ecological impact of a child, deserve very close scrutiny. There is a nuance between more or less conscious participation in ‘numerous causal chains’ and responsibility as such: ‘Is a doctor responsible for the future emissions of a patient whose life they save?’ It is clear that there is no simple trade-off between the value of human life and protection of the environment.
10 The closing chapter, on ‘fears and hopes in an uncertain future’, deals in particular with eco-anxiety, collapsology, and ‘communication through fear’. Without underestimating the risks to come, Pont recalls the importance of our collective ‘visions of the future’, and of ‘possibilities for action and change’.
11 At the end of his detailed analysis of the relationship between population and environment, and in light of the systemic nature of the potential changes facing our world, Pont downplays the importance of population as a means of addressing environmental problems. He writes, in conclusion, that ‘ceasing or refusing to have children will have only a minor effect compared to other determinants of the ecological crisis’. A distinction remains to be drawn between ‘population’ and ‘human activities’ in temporal perspective, recognizing that there is no interdependency between the number of human beings and their ways of life.
12 In conclusion, this is a stimulating book about questions of major importance, which are too often addressed without taking the measure of their true complexity. Among its merits are its clarity, its critical examination of current theories, its close examination of data, and its interdisciplinary approach to the interactions between environment and population. Its extensive bibliography also points the reader to many other sources.
An equation proposed in the early 1970s to quantify the environmental impact of human activities. According to this proposal, environmental impact, I, is the product of three factors: population size (P), population wealth (A, for affluence) and the technology available for the production of goods (T).