Revealing lethal spots: global tracking of extreme heat and human thermal stress using a new holistic class of climate hazard metrics

Weather and climate extremes such as extreme heat events are crucial, and increasingly lethal, climate hazards to people and communities worldwide. In any region, climate change may alter the characteristics of such events in complex ways so that a rigorous and holistic quantification of their extremity remains a challenge. This impedes hazard data users concerned with impact, attribution and litigation and likewise research, policy and practice users in the field of human health who are involved with reducing vulnerability and inequality, improving early warning systems and strengthening adaptation and resilience in severely-stressed regions.
Here we use a new holistic class of threshold-exceedance-amount metrics to globally track the extremity and amplification of extreme heat and human heat stress over land regions worldwide. We recently introduced these “TEA metrics” as a rigorous methodology and demonstrated their use through tracking heat amplification over Europe since the 1960s, revealing an over ten-fold increase of extreme heat over more than half of continental Europe (Kirchengast et al., Weather Clim. Extremes, https://doi.org/10.1016/j.wace.2026.100855). The metrics 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 as total events extremity.
For the worldwide tracking on land regions and per country we use daily maximum temperature as key variable for extreme heat (key thresholds TX99p, TX30, TX35) and the daily maximum universal thermal climate index (UTCI) for human thermal stress (thresholds TXutci99p local-region’s 99^th percentile in 1961-1990, TXutci38 very strong heat stress, TXutci46 extreme heat stress). State-of-the-art datasets are used over 1961 to 2025 (reanalyses ERA5, ERA5-HEAT; 0.25° x 0.25° grid) and core metrics results are provided online at the ClimateTracer.Earth data portal (“Extremes”; https://climatetracer.earth/ewm). Comparing the recent period 2011-2025 to the reference climate period 1961-1990, we reveal the most severely affected hot spots of heat stress, showing over thirty-fold amplification of total events extremity, further exacerbated if we also account for daily exposure time (using hourly key variable input data).
We discuss these results, and the prospective use of CMIP6 climate model data for extending the records through Shared-Socioeconomic-Pathways-based scenarios to 2100, and in particular discuss their significance and utility for downstream uses by scientific and practice users in the human health sector.