Meteorologists report that climate change is increasing the frequency and intensity of heatwaves across the globe [1, 2].
These events pose a critical threat to public health and infrastructure by pushing human physiological limits and straining energy grids. As baseline temperatures rise, atmospheric patterns like heat domes trap warm air over specific regions, prolonging extreme heat [2].
A heatwave is defined as a prolonged period of unusually high temperatures [1, 2]. While the Met Office defines it as at least three days of temperatures above 30 °C [1], other agencies define it based on temperatures exceeding a regional threshold for at least three consecutive days [2].
Recent data highlights the severity of these trends in Asia. India contains 95 of the world’s top 100 hottest cities [6]. In April 2024, dozens of Indian cities crossed 46 °C [6]. Specifically, 37 cities in Uttar Pradesh, 18 in West Bengal, and seven in Punjab recorded temperatures above 46 °C [6].
Beyond absolute temperature, humidity plays a lethal role. Samira Sadeque said that when the wet-bulb temperature exceeds 35 °C, the human body can no longer cool itself, making conditions potentially lethal [3].
Similar patterns have appeared in the West. In June 2024, a heat dome contributed to U.S. temperatures reaching up to 45 °C [2]. Helen Briggs said a heat dome is a high-pressure system that traps warm air, causing temperatures to soar dramatically and prolonging heatwave conditions [2].
Severe events have also been reported in Australia and the United Kingdom [1, 2, 4]. Looking ahead, projections suggest that summer 2026 is expected to shatter every heat record to date [6].
“India contains 95 of the world’s top 100 hottest cities.”
The convergence of rising global baselines and stagnant high-pressure systems creates a compounding effect. When extreme heat is paired with high humidity—measured as wet-bulb temperature—it creates a biological limit where perspiration no longer cools the body. This shifts heatwaves from manageable weather events to systemic humanitarian risks, particularly in densely populated urban centers in South Asia and North America.
