More than 61,000 people died because of last year’s brutal summer heat waves across Europe, according to a study published on Monday in the journal Nature Medicine.

The findings suggest that two decades of efforts in Europe to adapt to a hotter world have failed to keep up with the pace of global warming.

“In an ideal society, nobody should die because of heat,” said Joan Ballester, a research professor at the Barcelona Institute for Global Health and the study’s lead author.

This summer is likely to be even worse: On top of climate change, the Earth has entered a natural El Niño weather pattern during summer for the first time in four years, bringing about conditions that will turn up the heat in many parts of the world. The season is already shattering various global temperature records.

The researchers who studied last year’s heat waves used data collected by the European Union from 35 countries, including some nonmember states.

Most of the people who died were women, especially those older than 80. Among younger people, men died at higher rates. Mediterranean countries, where temperatures were highest at the time, suffered most: Italy, Spain and Portugal had the highest heat-related mortality rates.

Extreme heat had been expected that summer based on how much the planet had warmed overall in the past decade, Dr. Ballester said. When temperatures spiked, many European governments had “heat action plans” ready, developed in response to a more unexpected and deadlier heat wave in 2003, but those adaptations weren’t enough to prevent mass casualties, he said.

As climate change continues, the world can expect more and more deaths from extreme heat, Dr. Ballester added.

The European Union’s statistics office, Eurostat, regularly publishes the number of excess deaths (deaths above the expected average for a given time period) in European countries. Dr. Ballester and his colleagues took the official reports of total excess mortality from June through August 2022 and estimated how many of those deaths could be attributed to heat instead of other unusual factors like the coronavirus.

They used epidemiological models, meaning they matched recent historical temperature trends in different regions of Europe with mortality trends over the same period, to establish numerical relationships between deaths and temperature swings in those areas.

“When there is an up and down of temperature, we always observe an up and down of mortality,” Dr. Ballester said.

His team’s findings echo those of a study done shortly after the 2003 European heat wave, with some of the same collaborators. The earlier research found more than 70,000 excess deaths in Europe during the summer of 2003.

The previous study did not separate heat-related deaths from other excess deaths, so Dr. Ballester cautioned that the two numbers couldn’t be compared directly. The 2003 study also covered only 16 European countries, while the new study covers more than twice as many. When the researchers limited the results of this new modeling to those same 16 countries, they ended up with just over 51,000 heat-related deaths.

The researchers are working on applying the same epidemiological models to the 2003 heat wave to more precisely compare the two years. Barring drastically different numbers after a similar analysis, their results suggest that public policies adopted after 2003 have helped slightly reduce extreme heat’s toll.

In France, the more than 10,000 extra deaths in the summer of 2003 had political consequences, including the resignation of the country’s director general for health. Over the past 20 years, officials there and elsewhere in Europe have invested in early warning systems for extreme heat, public cooling centers, volunteer forces to check on older residents, and better coordination between social services and hospitals.

But the changes throughout Europe haven’t been enough. “It’s a spectrum” across different regions and populations, Dr. Ballester said.

Older people remain highly vulnerable, especially those without access to air-conditioning, and so are people who work outdoors. Older women were likely the worst-off group last summer simply because they live longer than men into the ages when people are most frail and likely to die during intense heat, Dr. Ballester said. He said other researchers have studied the reasons for demographic differences in mortality rates: For example, men tend to have worse health outcomes at younger ages, and some outdoor occupations, like construction, are dominated by men.

This paper did not compare deaths among people of different races or ethnicities, but that’s another important factor in vulnerability to heat, said Juan Declet-Barreto, a senior social scientist at the Union of Concerned Scientists who studies the health effects of environmental hazards and wasn’t involved in this study. While Dr. Declet-Barreto is less familiar with demographics in Europe, he said that in the United States people who work outdoors and are more exposed to heat tend to be immigrants of color.

Eurostat does not have a breakdown of excess mortality data by race, ethnicity or immigration status, an agency spokesperson wrote via email. Dr. Ballester and his colleagues recommended in their paper that the countries reporting to Eurostat better coordinate how they collect and share health data, including more demographic breakdowns. This year, the European Parliament proposed a regulation to do just that.

Even without additional demographic information, the study is “very timely” given this summer’s extreme heat, Dr. Declet-Barreto said. He thought the study’s methods seemed sound, given that “there’s a fairly well-known relationship in public health between heat and excess deaths.” He also agreed that comparing the 2022 and 2003 heat waves was helpful for revealing what health and policy interventions are still needed.

Four years ago, the International Federation of Red Cross and Red Crescent Societies published a guidebook to help city officials respond to heat waves, and its recommendations included changes to homes and physical infrastructure, like improving energy efficiency and ventilation.

Dr. Declet-Barreto said that he and other public health researchers have found that the most important factor in preventing deaths during heat waves is expanding access to air-conditioning.