Fig. 4.

Attribution of the direct CO₂ influence on the heatwave. (A–D) Maps of the ensemble mean attributable CO₂ signal in the heatwave for the four forecast lead times, which are indicated by the subplot titles. Stippling indicates a significant positive signal at the 90% level. (E) Boxplot of the absolute CO₂ signal for the three regions of interest and over the four forecast lead dates. Black line indicates ensemble median. Dark shading indicates 90% confidence in the median, and light shading indicates 90% confidence in the ensemble. Gray line indicates median difference between the operational forecast and PI-CO₂ experiment. (F) As in E, but showing risk ratios using the operational forecast as a factual and PI-CO₂ experiment as a counterfactual ensemble. (G) As in F, but using the INCR-CO₂ experiment as a factual and PI-CO₂ experiment as a counterfactual ensemble.