Figure 3: Return period plots of the observed maximum in daily maximum WBGT across World Cup host venues during the 39-day tournament period (11 June–19 July 2026) comparing the climate of 2026 (red; corresponding to the current World Cup period, with GMST of 1.3°C above pre-industrial levels) with the climate of 1994 (blue; the previous FIFA World Cup hosted in the United States, with GMST 0.7°C cooler than in 2026). The markers show the data and the lines show the expected return levels, with shading showing a bootstrapped 95% confidence interval. The dotted lines show the three (26°C, 28°C, 32°C) thresholds analysed in this study.