Climate change is increasingly affecting communities worldwide, posing a significant threat to human health and well-being (IPCC, 2022). Climate impacts can take various forms. Threats such as rising temperatures, shifting precipitation patterns, pervasive drought conditions, rising sea levels and glacial retreat evolve over longer time periods and alter ecosystems, agricultural productivity, livelihood opportunities and food and water availability. Simultaneously, rapid-onset events such as severe storms, flooding and wildfires are becoming more frequent, unpredictable and intense because of climate change, posing immediate and longer-term threats to those affected.

Importantly, the impacts of climate change are not distributed equally across time, space and different population subgroups. For example, generations born today are far more likely than their parents and grandparents to experience extreme climatic events in their lifetimes (Thiery et al., 2021). Moreover, the impacts of climate change will be more serious for places or people who are highly exposed to climate hazards and vulnerable to their effects, for example, because of poor health, low levels of education, poverty, or social and political marginalization. These factors can limit the capacity and the resources of individuals and communities to cope with and adapt to changes, and can thus exacerbate the impacts they experience.

Human populations are not only affected by the impacts of climate change, but are also its primary driver through the emissions they produce and other activities they engage in that contribute to environmental degradation. Over the last 150 years, human activities, particularly the emission of greenhouse gases through economic production, transportation, heating and other processes, have led to the warming of the atmosphere. While anthropogenic climate change is influenced by the number of people living on Earth, it is mainly caused by people’s affluence levels and their consumption and lifestyle patterns, which vary widely across the planet (Merchant, 2021; Muttarak, 2021). This results in deep injustices, as those who are the most affected by the climate crisis are typically those who have contributed the least to it (Zimm et al., 2024).

A growing interdisciplinary research community is seeking to improve our understanding of the myriad of interactions between humans, the environment and climate change by examining both the causes and the consequences of these complex relationships. Demography plays a key role in explaining these processes (Lutz et al., 2005; Muttarak, 2021). Demographic factors such as population size, composition and spatial distribution significantly influence both the causes and the consequences of climate change. For example, when populations are growing, the demand for resources and energy increases, potentially contributing to higher emissions. At the same time, population characteristics such as age and education structure can play an important role in explaining lifestyle and consumption differences, and hence the overall environmental footprint of a country.

Demographic factors and processes are also highly influential in determining differential vulnerabilities to climatic stress (Thomas et al., 2019). For example, children and older individuals are more susceptible to health risks associated with climate change due to their physiological characteristics, general health condition and reduced ability to cope with extreme events. Climate hazards can also disrupt the availability and accessibility of health services, for example, by destroying infrastructure or obstructing access routes. Such disruptions can be especially problematic in the context of reproductive health and rights, with pregnant women and mothers facing particular challenges and heightened vulnerability due to their specific health needs.

Migration is another important demographic process that can lead to populations moving to areas less equipped to handle environmental stress, including informal settlements, which often lack the infrastructure, sanitation and healthcare services needed to adequately respond to extreme events (Hoffmann and Muttarak, 2021). Increased urbanization in many parts of the world concentrates populations in areas that may be particularly vulnerable to climate-related hazards, further complicating climate change mitigation and adaptation efforts. On the other hand, this increased concentration can contribute to sustainability transitions by enhancing people’s well-being without exacerbating structural inequalities or placing additional strain on environmental resources (Adger et al., 2024).

To highlight the role of population in the causes and the consequences of climate change, this special issue of the Vienna Yearbook of Population Research (VYPR) brings together perspectives from 51 authors. The volume consists of 10 research articles covering issues related to the role of population in climate change mitigation, the impact of climatic factors on health and mortality, migration and reproductive behavior, and differential vulnerabilities and adaptive capacities, among others. These contributions employ diverse methodologies from the demographic toolkit and provide evidence from cases across various regions of the world.

In addition, the special issue includes seven Debate articles written by leading scholars in the field who discuss the importance of population and demographic trends for climate change mitigation, and how population policies can be used to tackle climate change. This unique collection of critical reflections complements the empirical articles, and is meant to provide readers with an overview of the current discussions, as well as the authors’ positions in these discussions, against the background of their research and the broader literature. The Debate articles discuss the significant role humans play in affecting the climate, albeit to greatly varying degrees, emphasizing the need for a nuanced perspective on populations’ contributions to global warming. They also underscore the importance of demographic data and rigorous evidence in supporting climate mitigation and adaptation efforts, while highlighting the urgent need for interdisciplinary collaboration and coordinated policy actions to understand and address the profound injustices of the climate crisis.

This introductory article first provides an overview of the climate-population nexus. In the following section, key insights from the literature on the relevance of population as a driver of climate change are presented. Next, the major impacts of climate change on population outcomes and dynamics are discussed in three sub-sections, with a particular focus on climate impacts on health and mortality, migration, and reproductive behaviors and fertility outcomes. As the impacts of climate change are expected to become even more detrimental in the future, the following section highlights the role of population projections and integrated forward-looking perspectives in capturing the full scope of the climate-population nexus and its implications today and in the future. Building on the contributions to this volume, we argue in the final section of this introductory article that a holistic demographic perspective is needed to understand the complex interplay between population dynamics and climate change, and to inform comprehensive policies and adaptive strategies aimed at mitigating its impacts.

Human populations are at the center of climate change and its impacts (Lutz et al., 2005). On the one hand, anthropogenic forces are responsible for the unprecedented changes in the climate system that are currently being observed. On the other hand, humans are directly affected by the resulting impacts. This bidirectional relationship, depicted in Figure 1, highlights the relevance of population as a driver of global climate change and its local impacts (left), and the multiple possible effects of changes in climatic conditions on population outcomes and the resulting dynamics (right). These processes are shaped by the economic, political, social and environmental context, which can influence mitigation and adaptation options, resource allocation, and the ability of people to withstand and cope with climatic impacts.

Humans influence the climate primarily through the emission of greenhouse gases related to various activities, such as burning fossil fuels for energy and industrial production processes, agriculture, transportation and deforestation. Technological advancements can play an important role in mitigating these emissions over the long term. However, whether these technologies can reduce emissions over the short and medium term continues to be debated. To combat climate change starting immediately, decarbonization as well as shifts in consumption habits and lifestyles are urgently required, especially in wealthier countries with high (historic) emission levels.

The accumulation of greenhouse gas emissions in the atmosphere causes global warming. Since the 19th century, global temperatures have increased by nearly 1.2 °C, with low latitude regions warming up particularly fast. This has led to a range of changes in local climatic conditions and extreme events, which are commonly referred to as climate change impacts. These include risks due to heat episodes, changes and increased variability in precipitation patterns, extreme weather events such as storms and flooding, sea level rise and increased drought and aridity.

These climate change impacts have been affecting communities worldwide. Here, direct and indirect channels of influence can be distinguished. Climate change affects humans directly by posing existential threats to their health and well-being in the form of shocks and physiological impacts. In addition, climate change exerts indirect effects on populations through its impacts on livelihoods, food and water security, social stability and peace. Both direct and indirect effects can influence key drivers of population change, including population health and mortality, migration and fertility patterns, with implications for the size and the composition of future populations in different parts of the world. These demographic changes will, in turn, determine the exposure and the vulnerabilities of future populations to climate events.

Both the responsibility for climate change and the consequences of climate change are not equally distributed. High-income countries, which are historically the largest emitters of greenhouse gases due to their early industrialization and high consumption levels, bear a significant responsibility for the current state of the climate. However, it is often the low-income countries and the most vulnerable populations within all countries that bear the brunt of the impacts. This imbalance highlights the profound injustice of climate change, as those who have contributed the least to the problem are often the most severely impacted, and thus face greater challenges in coping with and recovering from its effects.

Differential vulnerabilities are intrinsically linked to inequalities in societies, and to challenges in achieving just and inclusive development both within and across countries. At the same time, climate change also creates significant intergenerational injustices, as future generations will inherit the long-term consequences of climate change without having contributed to it. Thus, recognizing population heterogeneity is important for understanding both the causes and the consequences of climate change. Different population subgroups – both in the present and in the future – can have vastly different mitigation and adaptation options, while experiencing varying levels of exposure and vulnerability to climate change impacts.

How climate change will affect future populations and demographic trends over the short and the long term, and the role of global socioeconomic development in these processes, are the subjects of ongoing research. Using projection methods, demographers and population scientists are exploring the interplay of the different factors, and are developing scenarios describing potential population trajectories. Depending on the decisions taken by societies today, these scenarios can paint a more positive or a more negative picture. Policy interventions across multiple domains can play an important role in shaping the trajectories of population and socioeconomic developments, and in mitigating the risks associated with climate change in just and inclusive ways.

Population and population growth have long been discussed as drivers of climate change. Influential scholars such as Thomas Malthus, Garret Hardin and Paul Ehrlich have argued that overpopulation is the single most important and critical driver of environmental degradation and climate change (Bongaarts, 2023; van Dalen and Henkens, 2021). Although the topic had been discussed earlier, the overpopulation debate gained momentum during a time when global population was growing, peaking at an annual rate of 2.3% in 1963 (UN DESA, 2019). In their influential work, Hardin and Ehrlich used apocalyptic and unrealistic projections of future environmental conditions and food security to argue for drastic population control measures (Ehrlich, 1968; Hardin, 1968).

The efficacy and moral implications of such population control measures have been discussed by scholars. Referring to the neo-Malthusian population discussion, Pachauri argues in her Debate article (this volume) that the carbon footprint of childbearing decisions can be considered alongside the carbon footprint of any other consumption choice. However, the estimated carbon footprints of children and the assumptions about future consumption behaviors vary across studies. Moreover, Pachauri’s article underscores the importance of free choice, human rights and social justice considerations in climate change mitigation efforts, emphasizing that the environmental sustainability of individual consumption and fertility behaviors needs to be addressed in an ethical and just way.

Since the 1960s, population growth has declined, and increases in food production have out-paced population growth (Lam, 2023). Recent projections suggest that the global population will peak in the second half of the 21st century before starting to decline (Raftery et al., 2012; UN DESA, 2024). However, the discussion among demographers as well as the wider public about population as a major driver of climate change, and the potential need for population control measures, has persisted (van Dalen and Henkens, 2021).

The IPAT model (Liddle, 2014) provides a framework for formalizing the relationship between population and environmental impacts: it estimates environmental impacts (I) as a product of population (P), affluence (A) and technology (T). In her Debate article, Muttarak (in this volume) critiques this simplistic approach and discusses how it has been revised and refined to better account for spatial and socioeconomic heterogeneities, as well as other demographic characteristics, such as age, sex and education.

Importantly, the IPAT framework overlooks the reality that the benefits of technological developments are stratified along socioeconomic lines, with wealthier individuals within countries and populations in the Global North having better access to efficient technologies across various domains, such as housing, transportation and electricity (Vaishnav, 2023). In sub-Saharan Africa, for example, only 43% of the population currently have access to electricity, and the geographic coverage of electrical infrastructure is likely to remain limited over the coming decades (Dalla Longa and van der Zwaan, 2021). This disparity in technological access hampers climate mitigation efforts, as less affluent regions struggle to achieve climate neutrality.

Focusing solely on population numbers oversimplifies the complex dynamics of how populations affect climate change. As Adamo argues in her Debate article (this volume), population migration and urban-rural flows will increasingly influence the climate impacts experienced by different geographic regions and the potential for climate change mitigation in the future. The exclusive focus on population numbers also overlooks the significance of individual consumption behaviors. The consumption of animal-based products, individual travel choices and heating practices, among other behaviors, play a significant role in shaping the nexus between society and climate change impacts (Bruderer Enzler and Diekmann, 2019; Jorgenson et al., 2019; Rüttenauer, 2023).

According to recent estimates, two-thirds of global greenhouse gas emissions are linked to individual consumption, with the largest impacts coming from mobility and transportation, housing and nutrition (Ivanova et al., 2020). The carbon-intensity of people’s behavior follows a strong social gradient. On average, well-educated and higher-income households tend to have higher per person greenhouse gas emissions. In 2019, the richest 1% of the world’s population accounted for an estimated 16% of global carbon emissions – equivalent to the combined emissions of the poorest 66% of the world’s population, or five billion people (Khalfan et al., 2023). Women and older individuals generally have a smaller ecological footprint, and there is a complex relationship between urbanization and emissions (Liddle, 2014). This demographic and economic gradient in greenhouse gas emissions adds yet another dimension of social (in)justice (Bruderer Enzler and Diekmann, 2019).

Education is a crucial aspect of population heterogeneity that significantly influences climate change and its mitigation. Increased education is typically associated with a reduction in fertility rates, as it empowers women while simultaneously increasing economic activities (O’Neill et al., 2020). The extent to which these increasing economic activities impact climate change hinges on technological developments. Moreover, population dynamics often affect climate change through both direct and indirect pathways. In addition to influencing climate change via fertility behavior, education enhances the adaptive capacity of societies, thereby mitigating the potential negative impacts of extreme climatic events (Lutz et al., 2014).

Public opinions and attitudes toward climate changes are another important factor. Climate change beliefs and general values have been studied extensively as drivers of individual pro-environmental action (Steg, 2023). However, despite the growing awareness of climate change and the increasing support for green policies (Hoffmann et al., 2022a), climate-relevant behaviors and habits remain surprisingly resistant to change (Hoffmann et al., 2024; Rüttenauer, 2023; van Valkengoed and Steg, 2019). According to the problem of collective action (Olson, 1971), every individual has an incentive to freeride, waiting for others to undertake costly mitigation behaviors (Ostrom, 1998). In the end, everyone contributes less than would be optimal, in a situation akin to coordinating the cleaning of dirty dishes in a shared apartment with eight billion people. To address this problem and to effectively harness the changing attitudes of populations, societies need to redesign the incentive structures with monetary and non-monetary incentives such as green defaults (Liebe et al., 2021), and to implement carefully designed policy measures (Fesenfeld et al., 2022). Redistributive elements and the perceived fairness of these policy instruments play a vital role in enhancing public acceptance (Beiser-McGrath et al., 2023; Bergquist et al., 2022).

Population dynamics influence climate change through various complex pathways beyond sheer population numbers. Migration patterns, urbanization, education and socioeconomic factors shape the impact of populations on climate change – though precisely how populations affect climate change can vary depending on the specific context, the availability of technologies and individual consumption behaviors. Access to green technologies and their contributions to climate change through individual consumption choices are significantly influenced by economic resources, underscoring the importance of the issue of social justice in the relationship between population and climate change.

Climate change can affect demographic processes through its impacts on health and mortality, migration and fertility. Articles in this special issue document the various ways in which populations are affected, showing highly diverse effects across regional contexts and population subgroups.

Demographic projections are an important instrument in the demographic toolkit, both for enabling near-term public planning and assessing the long-term consequences of future anthropogenic global warming, biodiversity loss and environmental conservation. While the accuracy of population forecasts can only be evaluated ex post, demographers strive to base their future assumptions on the best available empirical evidence and to feed these assumptions into state-of-the-art models of population change, which are being applied to increasingly smaller spatial and temporal scales (Wilson et al., 2021).

Projections are particularly relevant for informing policymakers about the potential characteristics and dynamics of future populations. Madise et al. argue in their Debate article (this volume) that the future developments in the most populous and fastest growing countries will be particularly important. Despite their high absolute emissions, many countries in the Global South have very low per capita emissions. The future consumption patterns and economic development pathways in poor but fast-growing countries will thus become decisive variables in the mitigation of climate change. Madise et al. argue that “development aid must be available to ensure that poor countries can address their food security and energy needs with sustainable means” (this volume). Thus, current mitigation efforts should be viewed from a temporal perspective that considers historical inequalities and future population dynamics.

With regard to population-environment interactions, demographic projections help to anticipate future demand for essential resources, such as food, water, energy or land. This is highlighted by the contribution of Soltani et al. (this volume), who have studied the question of water scarcity in Iran under different fertility scenarios within a water-population system dynamics model. As Iran is situated in semi-arid to arid climate zones, water security has become an increasing concern in the country, especially given that the demographic transition has led to a rapid increase in population. By improving our understanding of future population trends and the spatial distribution of populations (considering internal as well as international migration), these projections can help researchers and policymakers assess the future strain on critical resources and ecosystems, as well as the likely implications in terms of greenhouse gas emissions.

The value of population projections is also showcased by Engström and Kolk (this volume). Relying on the well-established IPAT framework, the authors project the future ecological impacts of population growth in terms of both climate change and land use. In line with the Debate contribution by Lutz (this volume), the authors conclude that the role of fertility decline in reducing global warming via emissions might be smaller than was previously assumed, particularly if the effects of ongoing population growth can be partly mitigated by the use of improved technology. They warn, however, that the effects of population growth on future land use are harder to mitigate through technological advancements, thus increasing the potential impact of contemporary fertility choices.

Projections can be used not only to assess humanity’s impact on the environment, but also to identify vulnerable populations and to derive estimates of the exposure of future populations to the likely impacts of climate change (Muttarak, 2021). As shown by Soltani et al. (this volume) for the case of Iran, population growth can lead to increasing vulnerability to water scarcity, primarily for urban residents. But projections have also been used to assess the impacts of sea level rise in coastal areas around the world, where much of the population growth in the 21st century is predicted to take place (Hauer et al., 2019). In both of these cases, studying the underlying demographic trends can aid in the development of targeted adaptation measures aimed at strengthening the resilience of potentially vulnerable populations. Incorporating demographic data into climate models further improves the accuracy of future emissions trajectories, and, in turn, the effectiveness of climate policies. By simulating different scenario assumptions, projections enable researchers to assess the potential consequences of different policy options and to make better-informed decisions.

This central idea is also enshrined in the design of the Shared Socio-Economic Pathways (SSPs) (O’Neill et al., 2017). The SSPs are scenario narratives used to project and analyze future global changes in the domains of technology, economy and demography, and their environmental impact. Population plays a crucial role in the SSPs driving several other major outputs, including, for example, economic development, urbanization, labor force participation, resource demand and consumption, and vulnerabilities and adaptive capacities with respect to climate change. Moreover, understanding population dynamics is key for designing effective climate policies, such as those aimed at mitigating emissions through behavioral changes or technology adoption. While the SSPs cannot resolve the general problem of the uncertainty of future projections, the five different pathways described by the SSPs can help researchers explore the implications of ongoing developments assuming different future intervention strategies. By incorporating detailed demographic projections, the SSPs provide a comprehensive framework for assessing how different pathways of population growth and distribution will affect global sustainability and climate change mitigation and adaptation efforts.

Human and environmental systems are locked in a complex, dynamic and multi-dimensional relationship, whereby humans shape their environment and the environment shapes humans. Investigating and understanding the population-climate change linkages by looking at both the ways in which humans cause climate change and the ways in which climate change impacts human health, well-being and decision-making are core components of contemporary demographic science. Climate change impacts people’s daily lives, regardless of the speed or the geographic extent of the threats it poses. It influences livelihood strategies and childbearing plans, and has significant, long-lasting effects on individual behavior, migration decision-making and health and well-being outcomes.

A holistic demographic perspective is therefore essential for understanding the complex interactions between population and climate change, and for developing effective and equitable mitigation and adaptation strategies. As is shown by the articles included in this volume, investigating these linkages requires careful use of demographic data (often spatially detailed data) and associated demographic methods. Climate change investigations require population scientists to identify and quantify aspects of the environment across spatial and temporal scales that align with specific population processes or behaviors of interest. Thus, research on the climate change-population nexus is leading to advances in technical and data aspects of demographic sciences, while also pushing demographers to refine and refute foundational theories of population change and population-environment interactions (Grace and Merchant, 2022).

To meet this need for a comprehensive approach grounded in data, four points emerge from the literature published in this volume.