The Lancet Planetary Health, July 2025

Extreme heat and heatwaves: hazard awareness and impact mitigation

In the first two decades of the new millennium, almost half a million heat-related excess deaths occurred annually, with close to a quarter of a million deaths being located in Asia. As global warming continues unabated, these impacts of extreme heat are expected to increase further, highlighting the urgency for establishing effective early warning systems.

Compounding relationships between drought, heatwave, wild fire, persistent poor air quality (smoke related), and flash flood hazards have increased demand for improved multihazard early warning systems. The threat imposed by these compound hazards has been acknowledged under the UN’s Early Warnings for All initiative, which has targeted heatwaves as one of the priority hazards. However, many countries are yet to implement heat warning systems, and most of those that do have warning systems have poorly defined impact-based systems.