Climate change and international migration: Exploring the macroeconomic channel

distance are tested in our analysis. Our estimates of these variables are in many cases statisti- cally not significant or inconsistent. This is likely because inclusion of the diaspora variable already captures the effects of other dyadic variables to a large extent. At the same time, our parameter estimates are largely very robust against inclusion of additional dyadic variables. We report these results in the S3 Table in S1 File. It is important to point out that our model deliberately breaks with common gravity model specifications in order to be able to include the non-linear effect of origin income levels and to account for return migration and transit migration. These innovations are central for the analysis presented in this paper. The estimated global parameters for the migration model and the values of the parameters used for the climate change effect are reported in Table 1. The value of the country specific scaling factors are reported in the S2 Table in S1 File. 3 Results We estimate the impact of future global warming on global migration patterns via the indirect channel of national GDPc. We employ two methods of climate change impact on GDPc, pro- ducing two different patterns of GDPc changes due to global warming (Fig 1 and S2 Fig in S1 File). The baseline and perturbed trajectories of GDPc assume different patterns in terms of country- and population-weighted distributions, producing different responses in terms of the assumptions regarding the migration-hump function (Fig 2).

At the global level, under the CR case (constant emigration rates) we find that net change in global migration, i.e. the change in the total number of movements per 5-year period, on aver- age, reaches a maximum of * 0.1% (Fig 3a, light-colored bars). For almost all combinations of SSP scenario and impact method migration is projected to be smaller under climate change impact compared to the baseline. While the figure of the net difference in migration is infor- mative for the overall change in global migration, it does not provide full insight into the mag- nitude of the impact of climate change on migration flows, because climate change may reinforce some migration channels but inhibit others. Therefore, a more comprehensive pic- ture can be provided by looking separately at the total change in increased and decreased flows. We construct these figures by identifying all bilateral flows that are projected to decrease and all those that are projected to increase. We sum up separately these two set of flows, for both the baseline and climate change scenario, and then we show by how many percent these total number changes. Summing up these quantities we can define the migration movements that would be affected, either inhibited or reinforced. Under all the SSP scenarios and impact methods, the number of increases (i.e. additional moves due to climate change) is similar to the number of decreases (i.e. fewer moves due to climate change), summing up to a maximum of * 1.1% of total affected movements (Fig 3a, dark-colored bars). Positive and larger impact

is found in the net change of migration when considering the T0 case (migration transition, no change to migration hump function) (Fig 3b). The total number of affected migration movements remains substantially larger than the net change, reaching a peak of * 3% (increases of about 2%, decreases of about 1%) under SSP5–8.5, short-term method. When considering the TS case (migration transition, shifted migration hump) the impact on the net change remains small under SSP3–7.0 but increases substantially under SSP5–8.5 (Fig 3c). As for the CR and T0 case, the total movements affected by climate change is larger than the net change, in many cases being larger than 2-folds the value of the net change. Altogether these results can be summarized as follows: SSP5–8.5 produces larger differences in migration than SSP3–7.0, short-term impact method leads to larger effects compared to the long-term method and the TS produces lower differences compared to the T0 case. The climate change-induced PLOS ONE Climate change and international migration: Exploring the macroeconomic channel PLOS ONE | https://doi.org/10.1371/journal.pone.0276764 November 16, 2022 11 / 25