Climate change and international migration: Exploring the macroeconomic channel

return and transit migration are included explicitly in our model, following the methods in ref [26]. Data on historical country-level GDPc comes from the Penn World Tables (PWT, [27]) 8.1, reported in terms of 2005 purchasing power parity (PPP), and expanded for including missing countries using the PWT 9.0, after rescaling from 2011 to 2005 PPP [28]. Therefore, these his- torical values are consistent with the SSP projections data. We use future projections of GDPc under the SSP scenarios produced by the OECD [21]. Data on temperature changes is taken from a set of ten different GCMs (S1 Table in S1 File) available within CMIP6 [29] and bias corrected within the Inter-Sectoral Impact Model Intercomparison Project ISIMIP [30]. Global climate models are mathematical representations of the Earth system components, such as atmosphere and land surface, and of their coupling. These models simulate meteoro- logical variables, such as temperature and precipitation, in response to climate forcing from solar insolation, greenhouse gases, natural and anthropogenic aerosols, and other forcing fac- tors [31]. In this study we use the temperature variation estimated by these climate models. We calculate country-level area-weighted average temperatures starting from gridded data, and construct the temperature change ΔT as the difference between two subsequent time steps. For the period 2011–2014 the related temperature data comes from the output of the his- torical run of each climate model. Finally, the temperature of reference Ti(0) in Eq 4 is taken

from the observed data of Climate Research Unit (CRU). That is, in all our calculations, abso- lute temperature data come from observations, and only temperature differences are derived from climate models. When data was not available for some country, the temperature of the closest country has been used (S1 File). The values of the parameters used for the climate change effect on the GDPc, in Eqs 3 and 4 are taken directly from [13] and reported in Table 1. Table 1. Migration model and climate change effect parameters. Variable Parameter Value used Emigration and transit migration Intercept a 0.233 ± 0.004 Diaspora αp 0.943 ± 0.003 Dest. GDP αg 0.19 ± 0.01 Orig. GDP γ -0.0016 ± 0.0004 bG $ 35301 ± 9356 bG $ 929 ± 139 Return migration Intercept b 0.124 ± 0.001 R2 0.69 Climate change effect on GDP Cross-sectional αT -0.023 Panel α1 0.00641 α2 0.00345 β1 -0.00109 β2 -0.000718 Estimated values for the global parameters of the migration model, reported with a confidence level of 99% (for a, αp, αg) and 66% (for g; ~G; bG). The used values of the parameters entering the climate change effect methods are reported and come from [13]. https://doi.org/10.1371/journal.pone.0276764.t001 PLOS ONE Climate change and international migration: Exploring the macroeconomic channel PLOS ONE | https://doi.org/10.1371/journal.pone.0276764 November 16, 2022 5 / 25