Common myths about health risks from extreme and increasingly frequent heatwaves

Myths about the effects of extreme heat contribute to its human cost. Debunking them can save lives.

Vast areas of England, Europe, and the US continue to bake under extraordinary temperatures. In the last 30 days, more than 112.5 million Americans were under heat alerts. These will not be the only heatwaves this summer. Heatwaves are the number one weather-related cause of death in the US and Europe. Worldwide, there are more than 545,000 annual deaths from heatwaves. Yet nearly all deaths during a heatwave are preventable with sufficient advance preparation. Addressing myths about heatwaves can contribute to reducing preventable deaths. Here are a few of the more prominent ones.

1) I’m not at risk

All humans need to keep their core (internal) body temperature within a narrow range to protect their cells and organs. Humans have behavioral and physiological mechanisms to achieve that. Behaviorally, we seek out shady places or water bodies to cool down. Physiological mechanisms to dissipate excess heat include radiating heat to the environment; conducting heat by touching a cooler surface; transferring heat when cooler air or water contacts the skin (convection); and sweating to cool the body by evaporation.

Exposure to high temperatures over several hours may overwhelm the effectiveness of these mechanisms, resulting in a rise in the internal body temperature that then starts heating our internal cells and organs. This can ultimately lead to heatstroke, a medical emergency with a high fatality rate.

Everyone is susceptible to heat stress. A dramatic example occurred in 2001 when the 27-year-old Minnesota Vikings offensive lineman Korey Stringer died from exertional heat stroke during training camp. Another example was the death of a 23-year-old Brazilian student in 2023 during a concert by singer Taylor Swift . With nearly two-thirds of Americans living in counties vulnerable to heat threats, the individual stories are endless. For example, many delivery drivers and roofers have died from working in the heat.

Many groups are at higher risk during heatwaves, including older adults; young children; pregnant women; people with chronic medical conditions such as cardiovascular, respiratory, or kidney disease; people who take drugs, such as beta blockers, that reduce the ability of the body to sweat; and outdoor workers. Extreme hot temperatures are deadly, from heat stroke, cardiovascular disease, and nearly 70 other causes of death. People with epilepsy may experience more seizures; people with multiple sclerosis may experience exacerbations; and people with disabilities may suffer more. Some places also are at higher risk, such as redlined districts.

2) Few people die during a heatwave

The numbers of reported deaths during heatwaves significantly underestimate the true burden because those deaths are typically from heatstroke, which is a small fraction of total deaths. The total number of deaths are calculated based on a well-established and validated approach that counts the numbers of excess deaths; these are the numbers of deaths that occurred during a heatwave minus the numbers of deaths that occurred during the same period in earlier years. It can take months to a year before the death certificates required for these analyses are available. This limited visibility of heat-related deaths is why heat is a “silent killer”.

For example, for many years, the US Centers for Disease Prevention and Control estimated that about 700 people died annually from heatwaves in the US. CDC revised that estimate to about 2000 deaths in 2020. However, excess deaths analyses indicate about 12,000 deaths occur from the heat annually in the contiguous US. In Europe, which has more than twice the population of the US, 67,873 heat-related deaths occurred in 2022; 50,798 in 2023; and 62,775 in 2024.

3) Cold weather is more deadly than heatwaves

In countries such as the United States and regions such as Europe, there are many more deaths during the winter than the summer season. Because temperatures during summer have a strong, positive association with mortality, it is common, but incorrect, to assume that warming winters will reduce mortality, despite persistent comments on social media. Three lines of evidence support that cold temperature-related mortality is unlikely to be significantly reduced in future decades.

The first is observations that increasing temperatures over the past twenty years did not reduce cold temperature-related mortality. Despite warmer temperatures from 1985-2012, cold-attributed mortality increased in the US. Many cold-related deaths do not occur during the coldest periods or in the coldest places. Warmer US cities generally experience more mortality from extreme cold events and cold temperatures than colder cities. For example, hypothermia death rates are 66% higher in Houston than in New York City.

The second is that more deaths are categorized as occurring during colder than warmer temperatures because of statistical approaches used in analyses of temperature-related mortality. Every location has a temperature at which mortality is the lowest, with mortality increasing linearly as temperatures increase or decrease. The lowest mortality temperature is warmer than the average temperature, which results in more deaths associated with “colder” temperatures.

The third is that the leading causes of winter season mortality, cardiovascular, respiratory diseases other than influenza, and cancer, do not have strong associations with temperature. About half of winter season deaths is attributed to cardiovascular diseases. Seasonality in other factors may account for this, such as higher systolic and diastolic blood pressure in winter months along with changes in vasoconstriction, blood viscosity, red blood cell count, plasma LDL cholesterol, plasma fibrinogen, and possibly C-reactive protein.

4) Air conditioning is the answer

Most people can maintain their core body temperature during heatwaves without using air conditioning. Electric fans can be effective for many living in temperate climates, particularly when combined with misting with water to increase evaporation. Other options include putting your feet in cold water, draping an ice towel around your neck, and drinking cold water. Of course, air conditioning is needed by some people, such as those in frail health and others who struggle to maintain their core body temperature.

However, air conditioning is not feasible in many locations. Farms, highways, and many other outdoor environments can’t be air conditioned to protect outdoor workers. Regulations can ensure access to shade and sufficient hydration breaks, yet just seven US states have regulations to protect outdoor workers. And countries with high heat-related mortality, such as India, simply do not have sufficient electricity generation to protect the millions exposed to heatwaves.

Air conditioning has many downsides. Air conditioners pump heat outdoors, increasing the urban heat island. They can drive energy demand to the point of exceeding the supply capacity of the local utility. Blackouts during heatwaves amplify mortality and morbidity. This highlights that even in the US, it will take time to build the necessary resilience into the electric grid system. The situation is much worse in Europe given the nature of its housing stock. Further, air conditioning can increase emissions of greenhouse gas emissions that feedback to even higher future temperatures.

Heatwaves are a societal wide issue requiring comprehensive responses, coordinated across local to national levels, through heatwave action plans that include early warning and response systems. Hundreds are in operation worldwide, with more needed. For evidence-based approaches to effectively manage health, the website Heat.gov provides comprehensive information on how to protect families, friends, and colleagues from the risks of heatwaves.

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Kristie Ebi is principal in ClimAdapt, LLC.

Richard Richels was lead author for multiple chapters of IPCC studies in areas of mitigation, impacts and adaptation.

Gary Yohe is the receiving agent of Gary W. Yohe, LLC and Huffington Foundation Professor of Economics and Environmental Studies (emeritus), Wesleyan University.

Bud Ward spent five decades as an environmental and climate change journalist and educator.

Henry Jacoby is William F. Pounds Professor of Management (emeritus), M.I.T.