Climate change and international migration: Exploring the macroeconomic channel

like Africa are almost completely due to internal migration, which increases substantially in all regions (S5 Fig in S1 File). When considering the TS assumption we find very similar results as in T0 but with values reaching lower levels of relative difference (Fig 6c). Assumptions T0 and TS, compared to the CR case, producing projections of increasing regional bilateral migration flows show that, under the migration transition assumption, economic constraints at the origin country are a major factor inhibiting global migration movements and in general driving the patterns of both emigration and immigration response to economic climate change impacts. Values, in percentage, show the difference between the climate change case and the baseline in relative terms of the baseline case. Increases represent cases where migration under the climate change impact scenario is larger than in the baseline scenario. The external thicker arc defines the region of origin while the smaller internal arc shows the region of destination. Arrows point to the destination region. Flows represented are mean values for the period of 3˚C global warm- ing and averaged along the climate models dimension. 4 Discussion Given the severe and widespread impacts of climate change, and its potential to alter patterns of economic productivity and development, knock-on effects on international migration appear likely. In particular, if countries undergo a migration transition along with rising pro- ductivity, then productivity losses (or gains) due to climate change would slow down (or speed

up) this transition, and thus directly interfere with the long-term development of migration patterns. However, with current models and data this hypothesis can neither be validated nor invalidated with certainty. Against this backdrop, our study was meant to explore the range of potential outcomes. Using the most recent models for both, the dependence of global migra- tion on national incomes, and the impact of climate change on national incomes, and for a global warming level of 3˚C above pre-industrial, we have demonstrated the effects of climate change on migration through this particular macroeconomic channel, depending on what assumptions are made about the migration transition. We find that even when migration rates are assumed constant (CR), climate change may act to significantly increase some migration flows, and decrease others, by reorganizing the rel- ative attractiveness of destination countries. These changes are not visible in the net level of mobility, i.e. the global total number of moves, because increases and decreases cancel each other out; highlighting the importance of looking beyond global net effects when studying migration under climate change. Climate change impacts become much larger when countries are assumed to undergo a long-term migration transition along the emigration-GDPc relation- ship estimated from historical data (T0). In this case, the global total number of moves per 5-year period is projected to increase, by between half a percent and three percent depending

on the climate model and socio-economic development scenario. Again, this global number partly hides the full effect of climate change because some flows get increased while others get decreased. Finally, assuming that the emigration-GDPc relation is dynamic and shifts along with global average income (TS) leads to results that are in between the CR and T0 assump- tions; again affecting migration flows by several percentage points for many climate models and scenarios. Our results rely on two different methods for calculating economic effects from climate change impacts [13]. Expanding on previous approaches (e.g. [12, 39]), these methods are thought to improve the analysis on both spatial and temporal scales. Indeed, on the spatial scale they use subnational GDPc data, abandoning the long standing approach using national level GDPc. On the temporal scale they disentangle weather variability impacts (annual scale) PLOS ONE Climate change and international migration: Exploring the macroeconomic channel PLOS ONE | https://doi.org/10.1371/journal.pone.0276764 November 16, 2022 20 / 25