Sport-Relevant Heat Exposure and Socio-Economic Vulnerability: A Country-Level Assessment Under Coherent Shared Socioeconomic Pathways

(1) Background: Climate change is reducing the climatic windows in which outdoor sport and physical activity can be safely practised. Yet, it remains unclear whether the resulting population exposure is distributed evenly across countries or is concentrated in countries with higher socio-economic vulnerability. Here, we assess the country-level distribution of population exposure to sport-relevant heat along a projected socio-economic vulnerability gradient. (2) Methods: We assess a screening-level, population-based proxy of sport-relevant heat exposure, defined by residents living in grid cells experiencing specified afternoon WBGT exceedance frequencies. We first quantify a population exposure burden by combining reconstructed afternoon wet-bulb globe temperature (WBGT) exceedance frequencies from bias-corrected CMIP6 projections (NEX-GDDP, five-model ensemble) with SSP-consistent gridded population. The resulting grid-cell exposure burden, expressed in person-days yr−1, is aggregated to the country level. Countries are then ranked using a published national socio-economic vulnerability index (GVI), and the distribution of the exposure burden along this vulnerability gradient is quantified using a population-weighted concentration index (CI). The GVI is used as the ranking variable and is not incorporated into a multiplicative vulnerability-weighted risk metric. Two internally coherent futures (SSP1-2.6 and SSP2-4.5, each paired with its corresponding socio-economic pathway) are evaluated at mid-century (2055) and late century (2085). (3) Results: The population exposure burden is concentrated in more vulnerable countries in all scenario–horizon–threshold combinations (CI > 0; 0.09–0.25). Under SSP1-2.6 at mid-century, the five-model mean CI showed a descriptive increase from 0.17 for WBGT ≥ 28 °C to 0.25 for WBGT ≥ 32 °C, although the 95% paired hierarchical-bootstrap interval for the 32-minus-28 °C contrast included zero. By 2085, about 4.11 billion people live in cells experiencing at least 30 days yr−1 with WBGT ≥ 32 °C under SSP2-4.5, compared with 2.14 billion under SSP1-2.6. (4) Conclusions: The results identify projected between-country inequalities in resident population exposure to sport-relevant heat conditions; they do not quantify actual sport participation, athlete exposure or health outcomes. The comparison between SSP1-2.6 and SSP2-4.5 further shows substantial differences in both climatic hazard and population exposure between these two integrated climate–demographic–socio-economic futures.