Heat waves in Europe killed more than 61,000 people — most of them women — last summer, according to an estimate published in the journal Nature on Monday.

The summer of 2022 was the continent's hottest on record. Officials tallied thousands of "excess deaths" during that period, and this study specifically analyzes how many were a result of the heat.

Researchers analyzed data from the Eurostat mortality database for 35 countries to estimate that 61,672 people died from heat-related illness between May 30 and September 4. Italy, Spain and Germany had the highest number of heat-attributable deaths overall.

The staggering figure suggests that European countries are struggling to adapt to the effects of climate change, even in the wake of a deadly 2003 heat wave that caused more than 70,000 excess deaths across the continent.

The disaster led many countries (especially France) to implement heat prevention plans and other adaptation strategies aimed at protecting vulnerable populations, the study says, though "the evidence of their effectiveness is still limited."

"The fact that more than 61,600 people in Europe died of heat stress in the summer of 2022, even though, unlike in 2003, many countries already had active prevention plans in place, suggests that the adaptation strategies currently available may still be insufficient," researcher Hicham Achebak, one of the study's authors, said in a press release.

Without further action, the researchers warn, those numbers could continue to worsen drastically in the years ahead.

By 2030, the continent could see more than 68,000 heat-related deaths every summer. By 2050, each summer's deaths could top 120,000.

Prolonged waves of extreme heat are projected to increase significantly across Europe, especially in southern regions, Chiara Martinelli, the director of Climate Action Network (CAN) Europe, told NPR over email.

She stressed that heat waves are "extremely deadly" and disproportionately impact vulnerable, isolated and marginalized groups.

Martinelli is calling on governments to step up their efforts to limit global warming. And, along with the study's authors, she says these findings underscore the need for stronger heat prevention and adaption plans.

"Governments need to [prioritize] adaptation measures to be better prepared and deal effectively with extreme weather events, while ensuring the protection of all populations," Martinelli wrote.

Women and elderly people were most affected

The Nature study zooms in on specific countries and demographic groups to examine the impact of extreme heat.

It notes that Italy had the most heat-attributable deaths over the course of the whole summer, with 18,010, followed by Spain (11,324) and Germany (8,173).

Italy also ranked first in terms of heat-related mortality rate, with 295 deaths per million, followed by Greece (280), Spain (237) and Portugal (211). For reference, Europe's average was an estimated 114 deaths per million.

The researchers also looked at how much hotter the summer was than those in the past.

France fared the worst: Summer 2022 was about 4.4 degrees Fahrenheit hotter than the 1991 to 2020 average. Switzerland, Italy, Hungary and Spain were not far behind. And even that small-sounding number can have big health effects.

The authors say their findings emphasize the vulnerability of populations in Southern Europe.

"As a major climate change hotspot, these populations will be increasingly exposed to extreme summer conditions and would therefore be expected to experience increasingly higher heat-related mortality in the future," they explain.

The data also show a significant increase in mortality in older age groups — the vast majority of heat-related deaths were in people 80 years and up — and especially in women.

Women were much more vulnerable to the heat than men. Over the course of the summer, 35,406 women died, compared to 21,667 men.

The researchers do not explain why, but point to "physiological differences and sociocultural factors" among the potential explanations.

"We also found that differences in age structure between men and women partly explained the higher risk for women at advanced ages and for men at younger ages," they added, referring to the distribution of the population according to age.

What heat does to the body

Extreme heat can take both an immediate and long-term toll on the human body.

It can make people sweat more and cause dehydration, Dr. Ari Bernstein of the Harvard T.H. Chan School of Public Health told NPR last year. It can also directly create more heat in the body, which can keep the heart, brain, lungs or other organs from working properly. The consequences can be enormous.

"People who have existing heart problems, lung problems, kidney problems, even mental health issues, they get sicker," Bernstein said. "And even for people who are in generally good health, the heat can be really dangerous if we don't pay attention."

Other groups that are especially vulnerable to heat include infants, people in their 60s and older, outdoor workers with little control over their working conditions and people with certain health conditions or taking blood pressure drugs or other medications that can limit the body's ability to regulate temperature.

Extreme heat can lead to potentially deadly illnesses like heat exhaustion and heat stroke, and contribute to deaths from heart attacks, strokes and other forms of cardiovascular disease, according to the Environmental Protection Agency.

The Centers for Disease Control and Prevention offers guidance about how to spot and respond to signs of heat-related illness.

For example, someone experiencing symptoms of heat exhaustion should move to a cool place, loosen their clothes, sip water and get medical help if they start throwing up or see symptoms either get worse or last more than an hour.

If someone is suffering from heat stroke, they should be cooled down with wet cloths or an ice bath and receive medical attention immediately.

What Europe can do

The researchers call on European countries to reevaluate and strengthen their surveillance, prevention and adaptation strategies.

And they say those prevention plans should also "target a reduction of sex, age and other drivers of inequalities in the risk of heat-related mortality."

Adaptation strategies can take several forms, as Clean Energy Wire explains. They range from using technology to help infrastructure and people better cope with extreme weather, like building seawalls to protect against flooding, to nature-based solutions like planting trees to bring shade and reduce the temperature of the air.

The Red Cross Red Crescent Climate Centre released a 96-page guide in 2019 with steps that cities can take — before, during and after a heat wave — to reduce the risk and save lives.

It stresses actions like planning for the heat season, creating warning systems, improving public safety messaging and implementing urban planning strategies to manage heat risk in the long term. Some of those include green roofs, reflective or permeable pavements, car-free zones and water services.

There's also the question of limiting future warming. Martinelli, of CAN Europe, says countries must do more to meet the Paris Agreement target of limiting the temperature increase to 1.5°C (2.7 degrees F) above pre-industrial levels.

Future warming depends on future emissions, NASA chief scientist and senior climate adviser Katherine Calvin told Morning Edition on Wednesday. She says science can help people make decisions about what actions to prioritize.

"We know more about our planet than we ever have, there are scientists and engineers all around the world that are learning more every day, we're able to provide that information publicly," she said. "And we have options available today that can help us respond to climate change, whether that's options available to help reduce emissions or adapt to changes we experience, those all exist now."

What this all means for the U.S.

Europe's plight may hold lessons for other parts of the world, too.

The Southwest United States, for example, is experiencing extreme heat this week.

The country sees an average of 702 heat-related deaths each year, per the CDC. But specific heat waves, such as the one that hit the Northwest in 2021, have killed hundreds of people in a matter of days.

So why are the U.S. numbers so much lower than Europe's?

Experts say the heat could be more deadly in Europe because of the lack of air conditioning (only one in 10 European households had A/C as of last year, compared to nearly 90% of U.S. households). Plus, the U.S. could be underreporting its numbers, as one 2020 study found.

The CDC says some of those illnesses and death risks have diminished in recent decades, possibly because of better forecasting, heat-healthy early warning systems and increased access to air conditioning.

But, it warns, extreme heat events are still a cause of preventable death nationwide — and an ever-growing risk as the climate heats up further.