Extreme Heat



As global temperatures rise, the hottest temperatures and the number of areas affected by extreme heat are also on the rise. Extreme temperatures that only occurred once every 20 years in the 1960s now occur every 10 to 15 years and record highs are outpacing record lows by ever-greater margins. Even in recent years, during which global temperatures have not increased significantly, the total land area affected by extreme heat has increased. The length and frequency of heat waves are both expected to continue increasing through 2100.


Excessive heat can reduce or overwhelm the body’s ability to regulate its temperature, triggering conditions like hypothermia or heat stroke. More than 700 died during a heat wave in Chicago in 1995, and 2006 heat waves in California were responsible for 655 deaths, 1,620 hospitalizations and 16,000 emergency room visits. Additionally, power demand rises on hot days — especially in urban areas — and crops can be adversely affected. Some research suggests that a five-fold increase in the number of excessive heat event days across the 40 largest U.S. cities by mid-century is possible, nearly doubling the total number of excessive heat event mortality compared to 1975-2004.

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