Heat extremes in scenario projections: the role of variability

Heat extremes have grown disproportionately since the advent of industrialization and are expected to intensify further under unabated greenhouse warming, spreading unevenly across the globe. However, amplification mechanisms are highly uncertain because of the complex interplay between the regional physical responses to human forcing and the statistical properties of atmospheric temperatures. Here, focusing on the latter, we explain how and to what extent the leading moments of daily thermal distributions sway the future trajectories of heat extremes. We show that historical and future temperature variability are the key to understanding the global patterns of change in the frequency and severity of the extremes and their exacerbation over many areas. Variability is crucial to unravel the highly differential regional sensitivities and may well outweigh the background warming. These findings provide fundamental insights for assessing the reliability of climate models and improving their scenario projections.