heat wave

A high pressure system in the upper atmosphere traps heat near the ground, forming a heat wave (for North America in this example) Scorched grass in Greenwich Park, London, England, during a heatwave in August 2022. A heat wave or heatwave, sometimes described as extreme heat, is a period of abnormally hot weather and natural disaster that lasts for multiple days. A heat wave is usually measured relative to the usual climate in the area and to normal temperatures for the season. The main difficulties with this broad definition emerge when one must quantify what the 'normal' temperature state is, and what the spatial extent of the event may or must be. Temperatures that humans from a hotter climate consider normal can be regarded as a heat wave in a cooler area. This would be the case if the warm temperatures are outside the normal climate pattern for that area.

Heat waves have become more frequent, and more intense over land, across almost every area on Earth since the 1950s, the increase in frequency and duration being caused by climate change. According to the World Meteorological Organization, heat waves continued to intensify in 2024, with record-breaking temperatures reported in Europe, North America, and China. Many regions experienced consecutive days above 45°C, highlighting the increasing frequency and severity of extreme heat events worldwide.