# **1. Introduction**

Migration<sup>1</sup> constitutes a fundamental mechanism for reallocating labor across economic sectors and geographies to adapt to shocks, stresses, and imbalances. If managed well, migration can bring important gains at different levels and scales: it can improve the well-being and make more resilient the livelihoods of the families and communities of origin; it can ease labor market constraints in destination economies while at the same time alleviating un(der)employment pressures in places of origin; it can contribute to developing skills that migrants may bring back when they return home; and it can help people surviving violence, conflicts, natural catastrophes and environmental disasters caused by climate change. Achieving this requires implementing effective policies in all sectors, which in turn requires a thorough understanding of migration, its many nuances, and underlying causes and mechanisms at both the national and supranational levels (World Bank, 2023).

Although migration happens predominantly within borders, the number of international migrants in the world increased by more than 83 percent between 1990 and 2020, according to estimates from the United Nations Department of Economic and Social Affairs (UN DESA). However, the proportion of international migrants in the world’s overall population remains at less than 4 percent, with greater concentrations in high-income countries and most of these immigrants come from middle-income countries, with only a small share from low-income countries (UN DESA, 2020).<sup>2</sup> On the other hand, a lot of migration is currently happening within and across developing countries. For example, more than 50 percent of African migrants move within Africa, and this tendency is even more pronounced within regions such as West Africa where about 64 percent of migrants move to another destination within West Africa (UN DESA, 2020). Such movements have serious development and political implications and are currently animating public debate in many developed and developing countries, bringing renewed attention to the study of migration both in the scientific research community and among policy makers.

Despite this revamped interest, however, systematically measuring migration and its underpinnings remains a challenge, as also highlighted in the recent Global Compact for Safe, Orderly, and Regular Migration.<sup>3</sup> This is due to multiple factors but, above all, is the result of a paucity of accurate and regular data on migration, especially in low-income settings, and difficulties in reconciling information collected at different temporal and spatial scales regarding potential drivers and other important contextual factors (Parrish et al., 2020).

In 1990 the IPCC argued that the biggest impact of the changing climate might be on human displacement. Since then, the role of climate change in driving – directly or indirectly – migration has been progressively

> 1 Throughout this paper, the term “migration” is used in a broad sense, referring to all people who have moved away from their home (or usual place of residence) to live temporarily or permanently in another area in the same country or in another country, unless otherwise specified (e.g., internal migration, international migration, etc.).

> 2 Based on UN DESA data on international migrant stock in 2020, 65 percent of international migrants worldwide have high-income countries as their destination. In terms of origin, 65 percent of all immigrants in high-income countries come from middle-income countries, 25 per cent from other high-income countries, and only 6 percent from lower-income countries.

> 3 See: https://www.iom.int/resources/global-compact-safe-orderly-and-regular-migration/res/73/195.

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