A new class of climate hazard metrics and demonstration based on tracking extreme heat amplification 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 many 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 like as average event severity in a region, and up to compound total events extremity (TEX). Building on state-of-the-art daily and hourly temperature datasets over 1961 to 2024, we applied the new metrics to extreme heat events at local- to country-scale (example Austria, SPARTACUS 1-km-scale data) as well as across European land regions (whole of Europe, ERA5 10-km-scale data), demonstrating their utility through this example application. Comparing the recent period 2010-2024 to the reference climate period 1961-1990, we revealed about five- to twenty-five-fold amplifications of the TEX of extreme heat over Austrian and southern & mid-latitude European regions, finding these amplification signals strongly emerged from natural variability and an unequivocal evidence of anthropogenic climate change.

Given their fundamental capacity to reliably track any threshold-defined hazard at any location, the new metrics enable a myriad of uses beyond this example application. We hence close with summarizing such possible applications by scientific users but also practice users in the weather and climate services and action domains (e.g., hydro-met services, environmental agencies, insurance companies, law firms, public administrations, policymakers). These range from climate risk and impact analyses related to key extremes such as heatwaves, heavy precipitation, droughts, wildfires, flooding, and storminess to extreme events attribution, which quantifies the share of a hazard extremity, and optionally of its damage to properties and harm to people, that is estimated as attributable to anthropogenic climate change.