Fig. 2. Observed and simulated regional extreme event frequencies for the hottest day of the year (TXx).

(A) The map shows the difference in the mean value between the out-of-sample verification period (2006–2017) and the period for which the attribution metrics were calculated (1961–2005). (B) The red line shows, for each year of the 2006–2017 verification period, the observed northern hemisphere frequency of events in which the grid-point value exceeded the maximum grid-point value during the period for which the attribution metrics were calculated (1961–2005). The blue distribution shows the uncertainty in the hemispheric mean probability of exceeding the most extreme value found in the period for which the attribution metrics were calculated (1961–2005). The probability of the record-setting event is calculated by fitting an extreme value distribution to the 1961–2005 time series at each grid point, as described in (4); uncertainty is depicted by the percentile values of the bootstrapping described in (4). The blue circles show the regional frequency simulated by the CMIP5 climate model ensemble during the IPCC’s baseline period (1986–2005). The red circles show the regional frequency simulated by the CMIP5 climate model ensemble during the verification period (2006–2017). (C) The blue distribution shows the uncertainty in the regional-mean probability of exceeding the most extreme value found in the period for which the attribution metrics were calculated (1961–2005). The blue horizontal line shows the observed regional frequency during the IPCC’s baseline period (1986–2005); blue circles show the regional frequency simulated by the CMIP5 climate model ensemble during the IPCC’s baseline period. The red horizontal line shows the observed regional frequency during the out-of-sample verification period (2006–2017); red circles show the regional frequency simulated by the CMIP5 climate model ensemble during the verification period.