A new class of climate hazard metrics and its demonstration: revealing a ten-fold increase of extreme heat over Europe

Weather and climate extremes such as heatwaves are crucial climate hazards to people and ecosystems worldwide. In any region, climate change may alter their characteristics in complex ways so that a rigorous and holistic quantification of the extremity of such events remains a challenge, impeding also uses by climate change impact, attribution, litigation and other communities. Here we introduce a new class of threshold-exceedance-amount metrics that consistently track changes in event frequency, duration, magnitude, area, and timing aspects like daily exposure and seasonal shift—as separate metrics, partially compound (e.g., average event severity), and as compound total events extremity (TEX). Building on daily temperature datasets over 1961 to 2024, we applied the new metrics to extreme heat events at local-to country-scale (example Austria) and across Europe, demonstrating their utility through this use. Comparing the recent period 2010–2024 to the reference period 1961–1990, we reveal amplification factors of around 10 [5 to 25] in the TEX of extreme heat over Austrian and most central and southern European regions. This degree of amplification is found to strongly exceed the natural variability, providing unequivocal evidence of anthropogenic climate change. Given their fundamental capacity to reliably track any threshold-defined hazard at any location, the new metrics can support a myriad of uses beyond this example application. These range from climate impact analyses for extremes such as heatwaves, floods and droughts to extreme events attribution, quantifying the anthropogenic share of a hazard extremity and of its damage to properties and harm to people.