How fast is climate changing? One generation is sufficient for unfamiliar heatwave characteristics to emerge in Europe

We analyze the observed (1950–2020) and expected (2021–2050) change in temperature extremes and heatwave characteristics over Europe across time, and the emergence of unfamiliar (Signal to Noise ratio, S/N > 1), uncommon (S/N > 2) and unknown (S/N > 3) conditions from the ‘parents’ generation (1961–1990) to the ‘grandchildren’ one (2021–2050). Children born in 1991–2020 experienced conditions of extreme heat that were different from those at the time of their parents: at the European scale, 28.5—42.1% of the population in 1991–2020 experienced unfamiliar (and 1.3% uncommon) occurrence of extreme temperatures (Tx90p). Large areas of Spain, France, Germany, Poland, the Baltic states and Ukraine experienced a significant increase in heatwave number, and, together with southern Italy and Scandinavia, enhanced cumulative heat (HWC, with large areas where the signal has emerged from variability since 2011, but, locally, earlier. People born in the next 30 years (2021–2050) are estimated to live in a climate with extreme heat substantially different from that of their grandparents. In some regions, nobody is projected to live in conditions that were ‘familiar’ in 1961–1990. Even under a moderately-low warming, 41.8–58.6% of the European population is expected to live in conditions of unfamiliar extreme temperatures, 28.5–41.5% uncommon, and 2.1–8.9% unknown, mostly over Spain (5.3–26.9%), the Alps (1.2–27.5%) and the Mediterranean region (1.7–15.8%). The change in heatwaves characteristics will not only concern their number, but also their length and intensity, with more than 60% of the European population projected to be exposed to unfamiliar HWC and up 16.4% to uncommon HWC.