Heterogenous effects of Heat-Humidity Events on cognitive performance

Rising global temperatures increasingly expose populations to extreme heat, yet real-world evidence of how heat-humidity conditions affect cognitive function remains limited. Here, we build a unique data set using chess tournament outcomes as a proxy for cognitive performance. We analyse over 250,000 chess tournaments worldwide spanning 2003–2025 that include performance measures as specified by the international chess federations ELO rating system. By linking geolocated tournament results to climate reanalysis data, we quantify performance impacts across multiple heat stress metrics including daily maximum temperature, heat index, and wet-bulb globe temperature using panel-econometric methods that allow for causal interpretation. We focus on identifying heterogeneities of performance deviations by various dimensions such as player age, nationality, or skill. These heterogeneities reveal differential vulnerabilities that traditional laboratory studies cannot capture. Our results provide rare empirical evidence of heat's cognitive toll in naturalistic settings and establish a scalable framework for estimating productivity losses in service sectors, where cognitive work predominates but physiological heat thresholds applicable to manual labour are less relevant. As heatwaves intensify, understanding these cognitive impacts becomes critical for adaptation planning.