The Intergovernmental Panel on Climate Change (IPCC, 2022a, p. 1808) defines mitigation of climate change as “a human intervention to reduce emissions or enhance the sinks of greenhouse gases”. The design of these interventions and the selection of options require an understanding of mitigation behaviour, or human actions that directly or indirectly influence mitigation (IPCC, 2018, pp. 551), including the actions of individuals, communities, local organisations, governments and international organisations. Mitigation strategies or interventions may include plans or efforts to encourage changes in these behaviours, and thus to transform or modify human actions, in ways that contribute to climate change mitigation (IPCC, 2022a). This focus on human behaviour links the mitigation of climate change to population mobility trends, which are themselves the outcomes of human decisions, actions and conduct.

There are several mitigation options (i.e., technologies, processes or practices that reduce GHG (greenhouse gas) emissions or enhance sinks) that are implemented through mitigation measures, such as renewable energy (RE) technologies, waste minimisation processes or public transport commuting practices. Table 1 lists selected categories of mitigation strategies (Fawzy et al., 2020; Ivanova et al., 2020; Ginty, 2021; IPCC, 2022b), and looks at how mobility flows could either affect the strategies or be the result of their implementation.

Despite the widespread policy and media focus on international migration, the vast majority of movers remain within their countries’ boundaries. The number of international migrants has been estimated at around 280 million in 2020, or 3.6% of the world’s population (McAuliffe and Triandafyllidou, 2021, pp. xii). The numbers for internal migration are more uncertain and debatable: some sources have estimated the total number of internal migrants at around 763 million in 2005, or 12% of the world’s population, although in some countries the share of internal migrants in the population could be as high as 20% (UNESCO, 2018, pp. 13).

High-income countries are among the main destinations of international migration flows, and migration is an important contributor to population growth in these countries (United Nations Department of Economic and Social Affairs, Population Division [UN DESA], 2022). For internal migration flows, urban areas are the preferred destinations. Overall, the higher the level of urbanisation in a country, the lower the contribution of internal migration to population growth in urban areas; however, urbanisation processes and trajectories differ across countries (Menashe-Oren and Bocquier, 2021).

Population mobility is a highly selective process. In general, younger, more educated and higher skilled individuals are more likely than others to move, but there are, of course, differences in the characteristics of movers by region and type of flow (international vs internal, or seasonal vs permanent). In some contexts, women make up a large proportion of the movers (e.g., Guallar Ariño, 2023); while in others, education is negatively correlated with the probability of migration (e.g., Rendall and Parker, 2014). There are also contexts (e.g., Central American flows to the United States) where the proportion of unaccompanied children has recently been increasing (Rosenblum and Ball, 2016). Cumulative causation could lessen migration selectivity (Lindstrom and Ramirez, 2010).³

Because of this highly selective character, population mobility contributes not only to changes in population size and distribution in the sending and the receiving areas, but also to changes in the composition of the population by age, sex and educational status (among other demographic characteristics) in both areas (Rodríguez-Vignoli and Rowe, 2018; McAuliffe and Triandafyllidou, 2021).

At any given time, worldwide shocks could quickly affect population mobility trends. The effects of the COVID-19 pandemic and related measures and policies (including border closings, stay-at-home orders and travel restrictions) on all forms of mobility were widespread in 2020, 2021 and even 2022, reducing the scale of international migration; stranding passengers and migrants (McAuliffe and Triandafyllidou, 2021; UN DESA, 2022; González-Leonardo et al., 2023); and even reversing flows from cities to rural areas in some countries (Baumeister, 2020; Rowe et al., 2023). However, COVID-19 restrictions did not prevent major displacements and refugee flows due to conflict, violence, socio-political instability and environmental events (Internal Displacement Monitoring Centre and Norwegian Refugee Council, 2021).

Figure 1 displays the correlations between CO₂ emissions and GDP per capita (A); emissions and net migration (B); and emissions and urbanisation (C). There are large differences in emissions per capita across high-, medium- and low-income countries, and, overall, emissions per capita and GDP per capita are positively correlated (A). There is also a positive correlation between emissions per capita and net international migration rates, as migrants tend to move from the Global South to the Global North (international migration); in other words, from areas with lower emissions per capita to areas with higher emissions per capita. Similarly, higher urbanisation rates (used here as a proxy for internal migration) are positively correlated with CO₂ emissions (C).

In this context, population mobility could influence the reduction of GHG emissions (the main objective of climate change mitigation) in at least two ways: (a)

Population mobility alters the population size, growth and distribution trends in both the origin and the destination areas. In particular, it could lead to increases in population in areas where aggregated consumption and GHG emissions are already higher (e.g., large cities, high-income countries) (Morris, 2021; Jiang and Hardee, 2011; Liang et al., 2020). On the other hand, by reducing population growth in the origin areas, mobility could eventually reduce the emissions footprints of these areas. Liang et al. (2020, pp. 12534) summarised this point: “The developing regions are generally the net exporters of immiCO₂, while the developed regions mostly act as net importers of immiCO₂”.⁴ A critical caveat of these arguments is that they are based on the assumption that migrants follow the same emission and consumption patterns as non-migrants (Liang et al., 2020, pp. 12536), or that the populations in the sending and the receiving areas are homogenous in terms of their emissions and consumption patterns (Connolly et al., 2022). A similar argument could apply to urban and rural areas that are, respectively, the receiving and the sending areas of internal migration flows. In general, urban areas have larger carbon footprints than rural areas (e.g., Connolly et al., 2022; IPCC, 2022b; Sethi and Puppim de Oliveira, 2015), and rural to urban mobility could ultimately affect a country’s aggregated carbon emissions footprint (Long et al., 2022, pp. 10). However, this overall positive relationship between urbanisation and emissions can vary depending on the level of economic development and the form of urban settlement expansion (low, medium or high density) (Seto et al., 2010; Luqman et al., 2023). How rapidly a city expands in terms of population and area, and how concentrated or dispersed this growth is, are relevant factors in determining the city’s current and future role in the emissions of the country where it is located. The large body of existing literature on residential mobility and commuting (not covered in this brief article) – including transportation options and choices (active travel, public transportation, private car) – could provide valuable insights into this relationship (see, for example, Brand et al., 2021).

In this note, I looked at the ways that population mobility, as a key component of population trends, may shape emissions, consumption and mitigation behaviour, thereby facilitating or constraining mitigation strategies, options and policies. As people move within or between countries looking to improve their wellbeing or to escape conflicts, violence or disasters, population mobility needs to be acknowledged as a relevant factor in mitigation policies, not only at the national level, but also at the global level, for example, when setting global CO₂ mitigation targets (Liang et al., 2020).

The Global Compact for Migration recognises that migration is an inherent part of globalisation, and is essential for “connecting societies within and across all regions” (United Nations. General Assembly [UNGA], 2018, p. 3). It also calls for countries to “minimise the adverse drivers and structural factors that compel people to leave their country of origin” (UNGA, 2018, p. 9), including by implementing plans for mitigation of and adaptation to climate change.

At the same time, some mitigation plans, strategies and policies (such as negative emissions technologies based on the expansion of biofuels and carbon forests, geoengineering and solar engineering) could unintentionally result in forms of maladaptation that increase vulnerability and lead to displacement or forced migration (Ginty, 2021, pp. 1–2; see also Vigil, 2015; Sovacool et al., 2022; Aldy et al., 2021). Mitigation policies may have impacts on more disadvantaged groups (Hallegatte and Rozenberg, 2017), and mobility could be one of the responses to these effects.