recognized and increasingly studied (Hoffmann, 2020), gaining more prominence, and possibly also spurring more controversy, in the development research agenda.

Climate migration is not a new phenomenon. Human populations have historically used migration as a strategy to adapt and respond to changes in the climate (IOM, 2009). However, as these changes become more severe, widespread, and frequent, more and more people are expected to move as a consequence of both slow onset climate events and sudden climate shocks (Clement et al., 2021). As a result, the field of climate migration modeling has been evolving fast in recent years, allowing researchers to start quantifying this new phenomenon. The latest projections indicate that more than 210 million people will be forced to migrate within their own countries by 2050 due to climate change (Clement et al., 2021) with the poorest countries bearing the greatest burden (World Bank, 2021). While these figures have become accepted in the media (Lustgarten, 2020) and among specialized international institutions, it is also recognized that they come with caveats and do not often have empirical support in the literature (Letta et al., 2023). This is because, at present, climate migration models are based on fairly general assumptions about migration behavior due to a lack of reliable global datasets on climate-related human movements (McLeman, 2013).<sup>4</sup> Moreover, too little is known about the impact of climate change on international migration. Empirical efforts have focused mostly on modeling internal migration and evidence from the literature seems to support the view that most of the movements induced by changes in climate are currently occurring within national borders (rural-rural or rural-urban). While it is reasonable to assume that in the short-run climate-related migration is mainly a domestic issue, the latent potential for large-scale, international movements is often referenced in public discourse (Lustgarten, 2020) although poorly studied and substantiated by empirical evidence.<sup>5</sup> In particular, there is an absence of rigorous evidence on the interconnection between internal and international migration in the medium- to long-term (Cirillo et al., 2022) and the linkages with different types of climate change occurrences (slow-changes _vs._ rapid-onset shocks or their cumulative effect). Datasets on international migrants (especially on flows) are rare and outdated and, even when available, they rarely include the type of information that can be used to reconstruct the chain of migratory events potentially triggered by distinct climate change events or to understand behavioral responses and impacts at the micro level. Recognizing that repeated droughts, floods, progressive warming, sea level rise and desertification are much more important as indirect (rather than direct) drivers of cross-border mobility yields new, context-specific empirical questions – and associated data demands – regarding the channels through which this indirect mechanism operates. This suggests a change of perspective is needed to overcome the traditional distinction between “survival” migration and economically-driven migration, and consider the continuum (World Bank, 2023) and related intermediate outcomes that can act as push factors in determining international movements.

> 4 The study of climate migration involves the use of a variety of approaches many of which can be simplistic as they do not account for any behavioral aspects, or they do only to a limited extent (e.g., exposure mapping, gravity modeling). More refined approaches, such as agent-based models, that build on statistical and econometric analysis to model the behavior of different decision makers to climate-induced changes are still scarcely utilized as they require data on migration and key determinants at the micro level.

> 5 See section 2.2 for a more detailed discussion on this issue.

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