About 570 people in England and Wales are expected to die as a result of high temperatures from Thursday 19 June 2025 to Sunday 22 June 2025, a rapid study has estimated.

It is the first real-time analysis in 2025 on excess heat deaths by researchers at the London School of Hygiene & Tropical Medicine (LSHTM) and Imperial College London.

The study uses decades of U.K. data to understand risk relationships in 34,753 areas across England and Wales to predict the excess mortality during this heat wave.

Overall, about 570 excess deaths are expected to occur during the heat wave, the researchers estimate, with 114 on Thursday, 152 on Friday, 266 on Saturday when temperatures peak above 32°C and 37 excess deaths on Sunday when they fall to the mid-20s.

Older people above 65 are expected to be hardest hit, with 488 of the estimated excess deaths. Of these, 314 are expected to be among people aged 85 and over, the researchers found.

The results show how heat waves can be deadly for people with underlying health conditions such as heart problems, diabetes, and respiratory issues, as high temperatures put extra stress on their already compromised immune systems, the researchers say. However, they warn that heat can become life-threatening for all ages, as 82 deaths are estimated for people in the 0–64 age bracket.

The analysis also revealed London is expected to have the greatest number of excess deaths with 129, followed by the West Midlands with 106 deaths and the Southeast with 81. The difference is mostly due to where the heat is most extreme. However, the researchers say people living in deprived areas can experience higher rates of heat-related deaths because they have poorer health, housing and health care.

Professor Antonio Gasparrini, lead of the EHM-Lab at LSHTM, said, “Increases of just a degree or two can be the difference between life and death. When temperatures push past the limits populations are acclimatized to, excess deaths can increase very rapidly.

“A large number of the excess deaths likely wouldn’t have happened without climate change. To give an estimate, more research will be required.

“Clearly, a hotter climate is a more dangerous climate. Every fraction of a degree of warming will cause more hospital admissions and heat deaths, putting more strain on the NHS.”

Dr. Garyfallos Konstantinoudis, Lecturer at the Grantham Institute—Climate Change and the Environment, Imperial College London said,

“Heat waves are silent killers—people who lose their lives in them typically have pre-existing health conditions and rarely have heat listed as a contributing cause of death.

“This real-time analysis reveals the hidden toll of heat waves and we want it to help raise the alarm.

“Heat waves are an underappreciated threat in the UK and they’re becoming more dangerous with climate change. This weekend, people need to follow heat-health advice and check on older people, particularly those living alone.”

Dr. Malcolm Mistry, Assistant Professor at LSHTM, said, “Our study should be taken as a warning. Exposure to temperatures in the high 20s or low 30s may not seem dangerous, but they can be fatal, particularly for people aged over 65, infants, pregnant people, and those with pre-existing health conditions.

“Unless effective mitigation and adaptive measures are put in place in the coming years, the risk of large heat-related death events is set to increase in the U.K.—we have a large aging population and warming is expected to increase to 2°C by 2050 and as high as 3°C this century.”

This assessment highlights how extreme heat poses a growing threat to public health in the U.K. and follows a study published on Friday that found the heat wave about 10 times more likely and 2°C–4°C hotter due to climate change.

This week, the U.K. has experienced intense and sustained heat. On Tuesday, the UK Health Security Agency issued a yellow heat-health alert to warn vulnerable populations of the health risks posed by rising temperatures. By noon on Thursday, the situation escalated with a more serious amber alert covering all of England, warning of “a rise in deaths.” Soon after, dozens of people required treatment for heat-related illness at the Royal Ascot races as temperatures pushed above 29°C.

To estimate how many additional deaths could occur during the hot temperatures from Thursday to Sunday, the researchers used findings from published research on the relationship between heat and the number of daily deaths, regardless of the cause, in 34,753 small areas in England and Wales. They combined these mortality risk functions with high-resolution weather forecasts from Copernicus to estimate how many heat-related deaths will occur for four days in June.

An estimate of 570 deaths is in line with a previous study estimating nearly 1,100 deaths during the extreme heat wave from 17–19 July 2022, when temperatures reached 40°C in the U.K. for the first time, the researchers say. They also note that the analysis doesn’t account for the effect of the heat wave occurring early in summer before people are acclimatized to hot temperatures, meaning the heat deaths could be underestimated.

Climate change, caused primarily by the burning of fossil fuels, has already been shown to drive large increases in heat-related deaths. For example, about 56% of the 68,000 heat-related deaths during the 2022 European summer were caused by climate change, according to a 2023 study. The findings reflect how small increases in heat can cause huge increases in deaths when hot temperatures push people to their physiological limit, the researchers say.

The researchers say that a large number of the U.K.’s excess deaths wouldn’t happen without the heat boosted by climate change—temperatures are about 2°C–4°C hotter due to it, World Weather Attribution reported on Friday. However, they say it is unlikely the number of deaths linked to climate change would be higher than 50%, as reported in Europe where populations are vulnerable and the intensity of heat waves is rising faster than the U.K.

A recent report by the UK Climate Change Commission has estimated that heat-related deaths could rise to more than 10,000 in an average year by 2050 if ongoing fossil fuel burning causes warming to reach 2°C.