Keeping cool saves thousands of lives yearly, but at a cost of worsening global warming, experts say — Phys.org

RESOLVING THE LEDGER

This article has been reviewed according to Science X's editorial process and policies . Editors have highlighted the following attributes while ensuring the content's credibility:

Add as preferred source Cooling from air conditioning saves lives—more than 5,000 a year in the United States alone—but it also heats up the planet and taxes our electrical grid, scientists say.

As the world warms, heat waves strike nearly every continent and United Nations officials estimate that about half a million people die a year from heat, air conditioning is needed and being used more than ever. A study in Nature Health reported Monday that air conditioning saved nearly 58,000 lives between 2010 and 2020 in the U.S. Air conditioning use is skyrocketing around the world, with electricity demand from cooling expected to triple, according to the International Energy Agency and the United Nations Environment Programme.

It's also more of a problem than ever. Because most of the electricity for cooling comes from the burning of fossil fuels, the U.N. projects the amount of heat-trapping gas spewed into the atmosphere from air conditioning use to rise from 4.5 billion to 7.2 billion tons in the next 25 years or so. That 7.2 billion tons is almost as much as the carbon pollution from the United States and Europe now.

"Everyone knows air conditioning works, but air conditioning from a climate change perspective is not an ideal," said Kai Chen, an epidemiology professor at the Yale School of Public Health who was the senior author on the new study. "It leads to more carbon emissions ... then it accelerates the climate warming problem."

Because of a global energy crunch triggered by the war in Iran, eight countries—Bangladesh, Cambodia, Jordan, Malaysia, the Philippines, the Seychelles, Singapore and Sri Lanka—have limited how cool air conditioning can be in offices or even mandated one day a week for public offices to switch it off, according to the IEA. In 2025 the Indian government proposed limits on how cool air conditioners can go.

Experts from 75 countries and 250 cities are trying to walk the tightrope of creating more cooling to reduce deaths from the rising heat, but without worsening climate change. The Global Cooling Pledge will meet in September in Singapore.

One measurement experts use to tally accumulated heat as related to potential air conditioning use is something called "cooling degree days," a calculation of how much energy is needed to cool buildings when it's hot outside. The number of cooling degree days in the United States has increased by 28% since 1990, with 2024 setting a record, according to the U.S. Energy Information Administration . Through May, 2026 has been on pace to beat 2024 for the most cooling degree days, EIA data shows.

In Europe, the number of cooling degree days has more than doubled since 1990, and air conditioning use there has jumped up by 44%. Meanwhile, usage has tripled in India and more than doubled in Southeast Asia, the IEA reported.

In the new study, Chen and his team went through 30 million U.S. death records over an 11-year time span, used county-by-county calculations for levels when heat becomes dangerous and calculated how many lives air conditioning saved during extreme heat. The most lives saved were in Arizona, Florida, Texas, Louisiana and southern parts of Nevada, Alabama and Mississippi. More than a dozen northern states, from Washington to Maine, had fewer than 10 lives a year saved, according to the study.

Chen said the study concluded that "the essential role" of air conditioning saved on average 5,267 lives a year. But it also found that has to be balanced with "overuse." He pointed to offices—like his—which are cooled so much that many workers wear sweaters even in the summer. More than half the cases researchers looked at could be considered overuse, he said.

Many places use 75 degrees (24 degrees Celsius) as a reasonable limit for air conditioning, Chen said.

He also said the study found that using more air conditioning than needed doesn't save more lives, but it does worsen climate change.

Air conditioning in cities adds extra warmth to the urban heat island effect, as anyone who walks by air conditioning units knows because that's where waste heat is expelled outdoors, Chen said. And the added power use increases traditional soot and smog air pollution.

It's also an issue of fairness since many of the world's most vulnerable populations don't have access to or can't afford air conditioning, according to both Chen and U.N. officials.

Lily Riahi, head of the cooling buildings and energy unit at UNEP, said that in this year's heat waves, "many families had to choose between paying for medicines or running their air conditioner."

"In a warming world, thermal comfort should not be a luxury," UNEP chief heat officer Eleni Myrivili said. "It's becoming a prerequisite for health, dignity and increasingly survival."

Riahi said the goal is not less cooling but rather "smarter and more equitable cooling," and she pointed to Singapore as an example for effective solutions.

"Singapore is a country I think has really tackled cooling from a very comprehensive perspective, looking at individual adaptation measures, early warning systems, passive measures in the city in terms of urban greenery, which saves them, I think, $35 million in energy costs per year," Riahi said. Officials there also require new and old buildings to have more efficient cooling and ventilation systems.

Singapore has lowered temperatures in some places by 14 degrees (8 degrees Celsius), Riahi said.

But sometimes it can get so hot and humid in places that even green solutions aren't enough and air conditioning will be needed, Riahi said.

Until it's too hot and humid, fans and a low level of air conditioning work, Chen said.

Amruta Nori-Sarma et al, Impact of the summer 2025 heatwaves on emergency department visits in the USA, Nature Health (2026). DOI: 10.1038/s4...

Keeping cool saves thousands of lives yearly, but at a cost of worsening global warming, experts say — Phys.org | AIPROPX