<p>To date, research on heat extremes has primarily focused on acute events such as heatwaves. However, many regions of the globe currently face a heat hazard that can persist for months at a time. We call this hazard ‘chronic heat’ and define it here as potentially dangerous heat that lasts for 90 days or more per year. Analyzing 30 years (1993–2023) of global weather station data using three complementary metrics, this study reveals emerging shifts in global chronic heat patterns. 807 stations (20% of stations examined globally) meet the criteria for chronic heat over the entirety of this timeframe, and 215 stations (5%) have transitioned to chronic heat during it. Observed chronic heat predominates in the tropics, most stations transitioning to a chronic hazard occur in the subtropics across climate zones, and shorter-duration heatwaves remain centered in the mid-latitudes and polar regions. Increasing season-long heat hazard is an especially urgent concern in subtropical regions because they are often densely populated. Each metric analyzed—dry-bulb temperature, heat index, and wet-bulb temperature—shows somewhat different spatial patterns. Dry-bulb temperature patterns emphasize differences between arid and humid zones (43% vs. 6% of stations with chronic heat, respectively), heat index shows widespread chronic heat across climate zones, and wet-bulb temperature concentrates chronic stations in humid tropical coasts. The expansion of chronic heat is primarily driven by rising daily mean dry-bulb temperatures globally, with specific humidity enhancing chronic wet-bulb and heat index expansion. These differences underscore the need for multi-metric assessments, as humidity can make moderate temperatures dangerous for human health and dry heat can be dangerous without humidity. Increases in both the severity and extent of chronic heat underscore the importance of heat adaptations attuned to their unique risks for health and well-being globally.</p>