<mark>The next two sections s</mark> ummarize the empirical literature on climate change and migration and identify the main evidence and data gaps that could be closed by leveraging existing multi-topic household surveys as a starting point.

# **2.2 The status of the literature on climate change and migration**

In a recent data-oriented synthesis of the current state of empirical climate migration literature, Letta et al. (2023) notice that while the literature has grown exponentially in the last decades, this growth has not resulted in definitive evidence regarding the nature and magnitude of climate-migration nexus, nor in a clear-cut identification of transmission channels. There are two main reasons for this lack of correspondence between research output and conclusive evidence. The first is the nature of the subject matter itself: migration is per se an irreducibly complex and context-specific phenomenon and, when coupling it with the vast uncertainties surrounding the effects of climate change, it becomes clear how difficult it is to distinguish climate migrants from other types of migrants. The second, as already stated, is the existence of severe data gaps in developing contexts, especially at the microeconomic, longitudinal level. While precise figures of migratory flows induced by climate change are not likely possible, the literature equips us with four important and policy-relevant qualitative insights.

First, **evidence-based projections are needed** . Currently, there is no empirical evidence to support projections of sudden and massive migratory flows as a response to climate change, especially when referring to international migration. Instead, the available evidence suggests that climate-induced immobility, _i.e._ , a _decrease_ in migration in response to climatic shocks, is at least as important as climate-related migration. Immobility appears to be driven by the existence of liquidity constraints generated or aggravated by climate change, which makes it impossible for the poorest households to migrate in response to the shock. From this perspective, better-off households can choose who migrates in order to diversify risk and, as such, can be considered more resilient than those who are forced to stay. Furthermore, when weather shocks and climate volatility do trigger mobility responses, the literature recognizes that these are predominantly internal, ruralurban movements rather than costlier, longer-distance cross-border flows. As already pointed out, this is in stark contrast with the predominant attention international climate migration usually receives in the policy arena.

Second, **slow-onset changes matter more than fast-onset shocks** . Slow-onset changes such as repeated droughts, progressive warming, and desertification are more likely to induce longer-term or permanent migration compared to fast-onset shocks such as hurricanes, storms, and floods. Slow-onset events are also more closely linked with possible immobility traps in rural and agriculture-dependent areas in poor countries.<sup>15</sup> The bifurcation of the migration response in the face of slow-onset changes – immobility _vs._ mobility – seems

> 15 In principle, fast-onset shocks may also lead to immobility, as they can quickly deplete households’ financial resources (Kaczan & Orgill Meyer, 2020). In practice, however, the most widespread consequence of sudden events is displacement or forced relocation. 8