How do heatwaves kill?
Although not record-breaking, for much of Europe, the summer of 2023 was another hot one. According to data from the Copernicus Climate Change Service, the average European temperature for the summer was 19.63 °C, 0.83 °C above average, making it the fifth warmest summer season on record. For parts of Europe, it was also a summer of heatwaves, with much of southern Europe seeing a record number of days with extreme heat stress. Southern Spain was particularly impacted, experiencing at least 60 days with real-feel temperatures of between 38 °C and 46 °C and some areas even seeing the mercury exceed 46 °C for as many as 15 days. But heatwaves are more than just uncomfortable – they’re also deadly. In 2022, during which Europe saw its hottest summer ever, nearly 62 000 people died from heat-related stress. “When the body’s temperature rises above 40.6 °C, there is an acute risk of heatstroke that, if left untreated, can cause organ damage, circulatory collapse, unconsciousness, and in the worst case, death,” says Aunan, research director at the Center for International Climate Research. According to Aunan, there are many reasons for increased mortality during heatwaves or generally high temperatures. “Heatwaves usually bring with them a risk of dehydration, poor sleep and reduced overall well-being, all of which can increase people's vulnerability,” she adds. Acute exposure to high temperatures also causes the body’s built-in cooling system to kick in. To do so, blood is redirected from internal organs to the periphery, sweat glands are activated and excess heat is transferred to the surroundings. “This thermoregulation process is powered by the cardiovascular system, which must work harder, meaning an increased heart rate,” explains Aunan. But this increase in cardiac workload, in combination with a reduction in plasma volume caused by sweating, can result in an increased risk of blood clots – clots that in turn can cause strokes and heart attacks.
High-risk groups
Because effective thermoregulation depends on a well-functioning cardiovascular system, some populations are at a higher risk of overheating, heatstroke or heat-related death. This includes not only those individuals with underlying cardiovascular disease, but also older adults in general. For example, heat can cause dehydration, which often leads to low blood pressure – particularly detrimental to the elderly already on blood pressure-lowering medications. “Increased vulnerability in older adults can be partially attributed to existing disease, medication use, a decline in thermoregulatory function and reduced cognitive function,” adds Aunan. Vulnerability can also be associated with life circumstances, such as living alone, having a limited social network or suffering from reduced mobility. Research conducted by the EU-funded EXHAUSTION project, which Aunan helped coordinate, shows that increased vulnerability in disadvantaged groups can be explained by this reduced adaptability. “Lifestyle-related risk factors and poor health status, along with a lack of access to air conditioning and healthcare services, makes society’s most vulnerable populations particularly vulnerable to the effects of heatwaves,” remarks Aunan. With Europe set to experience another summer of scorching temperatures, researchers including Aunan are helping us better understand the associated health risks, and create a safer and healthier future for Europeans. Find out more about Kristin Aunan’s research: Heatwaves and air pollution combined: Europe’s silent killer
Keywords
EXHAUSTION, climate change, heat, heatwave, heatstroke, death