After three of Earth’s hottest days ever measured, the United Nations (UN) called for a flurry of efforts to try to reduce the human toll from soaring and searing temperatures, calling it “an extreme heat epidemic.”

“If there is one thing that unites our divided world, it’s that we’re all increasingly feeling the heat,” United Nations Secretary General Antonio Guterres said on July 25 at a news conference where he highlighted that Monday (July 22) was the hottest day on record, surpassing the mark set just a day earlier.

“Earth is becoming hotter and more dangerous for everyone, everywhere.” Nearly half a million people a year die worldwide from heat related deaths, far more than other weather extremes such as hurricanes and this is likely an underestimate,” a new report by 10 U.N. agencies said.

“Billions of people are facing an extreme heat epidemic — wilting under increasingly deadly heat waves, with temperatures topping 50 degrees Celsius around the world,” Mr. Guterres said. “That’s 122 degrees Fahrenheit and halfway to boiling.” The dire warnings came after a barely noticeable respite in back-to-back record global heat.

The European climate service Copernicus calculated that Tuesday’s global average temperature was 0.01 Celsius (0.01 Fahrenheit) lower than Monday’s all-time high of 17.16 degrees Celsius (62.8 degrees Fahrenheit), which was .06 degrees Celsius hotter (0.1 degrees Fahrenheit) than on Sunday. All three days were hotter than Earth’s previous hottest day in 2023. “We are not prepared,” the U.N. report said.

Mr. Guterres urged countries of the world to adopt several proposals aimed at reducing heat deaths, starting with help to cool and care for the most vulnerable people — the poor, elderly, young and sick.

The UN also called for better heat wave warnings, expanding “passive cooling,” improved urban design, stronger protections for outside workers, as well as greater efforts to tackle human-caused climate change that’s worsening weather extremes.

But officials said most work will have to be done by countries, with the U.N. offering aid and coordination, especially when it comes to beefing up weather warning systems.

If countries adopt the United Nations heat-fighting recommendations, “these measures could protect 3.5 billion people by 2050, while slashing emissions and saving consumers $1 trillion a year,” Mr. Guterres said, citing a U.N. Environment Programme estimate.

“Better heat-health warning systems in 57 countries could save 98,314 lives per year,” the report said, based on World Health Organization and World Meteorological Organization estimates.

“Crippling heat is everywhere, but it doesn’t affect everyone equally,” Mr. Guterres said. “Extreme heat amplifies inequality, inflames food insecurity and pushes people further into poverty.” More than 1,300 people died during this year’s annual Haj pilgrimage after walking in scorching heat.

Earlier this year, India’s prolonged heatwaves resulted in the deaths of at least 100 people. However, health experts say heat deaths are likely undercounted in India and potentially other countries.

Last year, the United States had its most recorded heat deaths in more than 80 years, according to an Associated Press analysis of Centers for Disease Control and Prevention data. The death certificates of more than 2,300 people mentioned excessive heat, including 874 deaths in Arizona.

Deadly heat is not new, but scientists say it has been amplified in scale, frequency and duration with climate change.

Extreme heat, wildfires, floods, droughts and ever more fierce hurricanes are symptoms and “we need to fight the disease,” Mr. Guterres said. “The disease is the madness of incinerating our only home. The disease is the addiction to fossil fuels. The disease is climate inaction.” “Many things are being done, but too little, too late,” he said. “The problem is that climate change is running faster than all the measures that are now being put in place to fight it.” Before July 3, 2023, the hottest day measured by Copernicus was 16.8 degrees Celsius (62.2 degrees Fahrenheit) on August 13, 2016. In the last 13 months that mark has now been beaten 59 times, according to Copernicus.

Humanity is now “operating in a world that is already much warmer than it was before,” Copernicus Director Carlo Buontempo said.

“The steady drumbeat of hottest-day-ever records and near-records is concerning for three main reasons. The first is that heat is a killer. The second is that the health impacts of heat waves become much more serious when events persist. The third is that the hottest-day records this year are a surprise,” said Stanford University climate scientist Chris Field.

Field said high temperatures usually occur during El Nino years — a natural warming of the equatorial Pacific that changes weather worldwide — but the last El Nino ended in April.

Field said these high temperatures “underscores the seriousness of the climate crisis.” “Unfortunately people are going to die and those deaths are preventable,” said Kristie Ebi, a public health and climate professor at the University of Washington. “Heat is called the silent killer for a reason. People often don’t know they’re in trouble with heat until it’s too late.” “At some point, the accumulated heat internally becomes too much, then your cells and your organs start to warm up,” Ebi said.

“The “big driver” of the current heat is greenhouse gas emissions, from the burning of coal, oil and natural gas,” Mr. Buontempo said. “Those gases help trap heat, changing the energy balance between the heat coming in from the sun and that escaping Earth, meaning the planet retains more heat energy than before,” he said.

“Other factors include the warming of the Pacific by El Nino; the sun reaching its peak cycle of activity; an undersea volcano explosion; and air with fewer heat-reflecting particles because of marine fuel pollution regulations,” experts said.

Mr. The last 13 months have all set heat records. The world’s oceans broke heat records for 15 months in a row and that water heat, along with an unusually warm Antarctica, are helping push temperatures to record level,” Mr. Buontempo said.

Growing up in the 1990s in India meant having seen an ad for a glucose-based drink on television in which the Sun literally sucks the life-force out of children with a giant straw as they are playing. This ad has started to hit closer to reality. India has increasingly been in the grip of more frequent and intense heat waves, with outdoor workers especially struggling with the rising mercury.

A recent study published in Science Advances showed that it wasn’t just India: the whole world is grappling with slower and longer heat waves.

Temperature and circulation

Heat waves have a terrible impact on human and animal life, with increased risk of wildfires, damaged crops, and worse health. Analysing temperatures around the world from 1979 to 2020, Wei Zhang, a climate scientist at Utah State University, and his colleagues studied how they have changed over time.

On average, they found, heat waves have slowed down nearly 8 km/day each decade and lasted longer by about four days — the effects being particularly drastic in North America and Eurasia. Heat waves have also increased in frequency, from about 75 events averaged over 1979-1983 to about 98 over 2016-2020.

“In thinking about heat waves and how they would change in the future, there are two pieces of the puzzle that climate scientists think about,” Rachel White, an atmospheric scientist at the University of British Columbia, said. “One of them is thermodynamics: it’s just about the temperature. As temperatures are getting warmer, heat waves are going to get warmer. The second piece is the dynamics: the atmospheric circulation patterns that cause heat waves.”

There are still some open questions around how those might change in a warming world.”

The heat moves

Previous studies have mostly focused on how frequent heat waves are or how hot it gets during one. In this study, the researchers classified contiguous heatwaves as events with extremely high temperatures, covering more than a million square kilometres, and lasting for longer than three days. They then tracked the movement of these huge masses of hot air over space and time, studying how far and how fast they were moving – one of the first groups of scientists to do so.

Instead of just focusing on the frequency and the intensity of heatwaves, the study also checked how fast they were propagating and how long they lasted. By looking at how heat waves move over time and space, Dr. White believes the study has bridged the gap between the thermodynamic and dynamic pieces of the heat waves puzzle a little more than before.

“This study is looking at heatwaves like an object that can move and can travel and propagate, which you would miss if you were just looking at one point,” she said. “If you just look at one point, you can be like, ‘oh, the heat wave lasted for 5 days’. But the object itself lasted for longer, it just moved. That’s what they are doing here, tracking them as they are moving, which is cool.”

The guiding hand falters

But what could be causing them to move so sluggish? The scientists analysed the upper atmosphere’s air circulation patterns, to see how the moving air could affect these big blobs of heat. They found that over the years, the jet stream — a fast, narrow current of air that flows from west to east high up in the troposphere — has become weaker.

The jet stream guides atmospheric waves, waves that are caused by the earth’s rotation and which influence the earth’s surface temperature. As the jet stream weakens, these waves also move more slowly, leading to more persistent weather events, and more spells of high and slow-moving heat.

To check if human activity had played a role in this outcome, the researchers ran simulations with temperature data from 1979 to 2020, but included scenarios with and without human greenhouse gas emissions. They found that though natural climate variability and natural events also influenced how heat waves had changed, human activity and greenhouse gas emissions have played a dominant role in rendering the slower-moving and longer-lasting heat.

Dr. White said the next steps would be to further tease apart the role of atmospheric air circulation patterns in contributing to heat-wave dynamics on the ground. Country-specific changes in heat waves over time would also be some of the missing pieces of the puzzle she would like to see. “I think there’s just a lot that can be done with this dataset, now that they have created it,” she said.

Heat waves are changing

Dr. Zhang does plan to delve deeper into regional differences as part of the group’s next steps, while also working on climate adaptation strategies. “Given that heat waves have such a huge impact on human health and the environment, we need to think about climate adaptation,” he said.

In densely populated urban areas, some strategies to better mitigate changes in heat waves would be to plant more trees and increase green infrastructure – an undertaking Dr. Zhang has himself been involved in. Together with Tree Utah, an NGO, he has been engaging people in planting and taking care of trees. He has also been teaching a class on Climate Adaptation Science at Utah State University, where he helps students learn and apply climate adaptation strategies, with projects like working with farmers on alternative crops.

“This paper is another form of evidence that climate change is altering these extreme weather events,” Dr. Zhang said. Adding to the already long list of studies, like how the intensity of hurricanes has increased or how there is extreme precipitation, this study, in Dr. Zhang’s words, “is another signal of how climate change could influence our daily lives, our health, our environment — by changing the behaviour of heat waves.”

Rohini Subrahmanyam is a freelance journalist.