Why Heatwaves Are So Dangerous for Humans

Extreme heat poses a significant threat to human life, as demonstrated by a sharp rise in mortality during a recent heatwave in France. Between June 22-28, the country registered 2,025 more deaths than usual, a preliminary figure representing a 29.1 percent increase from the previous week. Health authorities anticipate the final toll will be considerably higher.

The human body struggles to cope with intense heat. The heart is particularly strained as it works harder to transport blood to the skin's surface to dissipate heat. This can lead to severe heart failure in some individuals. Increased sweating, if not compensated by adequate fluid intake, thickens the blood, raising the risk of clots. Kidneys also suffer as they regulate fluid and salt balance; higher temperatures demand more water, increasing dehydration risk and potential kidney issues.

While young, healthy individuals often tolerate heat well, the elderly, those with pre-existing medical conditions, pregnant women, and children under five are at greater risk. These groups have less efficient thermoregulation or compromised organ function. Recent studies, including one in Nature, suggest that over 61,000 Europeans died from heat-related causes in the summer of 2022 alone.

Even in Sweden, higher mortality rates are observed during warmer periods. In the summer of 2018, approximately 700 more Swedes died than normal, with researchers attributing most of these deaths to heat. Defining a precise dangerous temperature is difficult; research indicates that mortality risk begins to increase even at moderate temperatures, rising nearly linearly with each degree Celsius above a certain threshold.

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Under extremvärmen i Frankrike 22-28 juni registrerades 2 025 fler dödsfall än normalt