Hot days or heat waves? Researchers debate how to count deaths from heat
Focusing on temperature extremes can galvanize policy changes but risks undercounting.
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Some argue the best way to understand the impact of heat is to track how death rates vary with fluctuations in temperature, as the European studies did. But others say a truer measure is to rely on officially declared heat waves and count excess deaths—those above the expected number—each day.
The two kinds of studies “provide answers to different questions, looking at different exposure metrics,” says environmental epidemiologist Jaime Madrigano of Johns Hopkins University. Seeing how deaths vary with temperature captures the health effects of gradual warming, whereas focusing on heat waves highlights the consequences of extreme cases.
The dispute isn’t just academic. Heat waves grab headlines and the attention of policymakers, spurring them to adopt heat warning systems that urge people to stay indoors or take other precautions. But some scientists note that just examining heat waves omits the deaths that occur beyond what’s considered extreme.
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Heat stroke is the most extreme and direct effect of too much time exposed to high temperatures. But it only accounts for a minority of the toll. Deaths from many other causes also rise, for example when heat tips someone with an underlying heart condition into a fatal heart attack.
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