Heat Waves and Rising Extreme Temperatures

The IPCC's Sixth Assessment Report (Working Group I, 2021) concludes with high confidence that the frequency, intensity, and duration of heat waves have increased over most land areas since the 1950s, and that this trend is virtually certain to continue as global mean temperature rises. A heat wave is generally defined as a period of abnormally high temperatures, often combined with high humidity, that persists for several consecutive days relative to the local climatological baseline; national meteorological services such as the U.S. National Weather Service and India's IMD apply their own thresholds, but the underlying physical driver is the same shift of the entire temperature distribution toward higher values, which disproportionately increases the frequency of extreme tail events. The European heat wave of summer 2003 remains a benchmark case: an epidemiological reconstruction by Jean-Marie Robine and colleagues, published in Comptes Rendus Biologies (2008), estimated roughly 70,000 excess deaths across Europe, with France alone recording about 15,000, concentrated overwhelmingly among the elderly and those without air conditioning in dense urban housing.