UK Heat Deaths Halved Despite Warmest Summer on Record

LONDON. The UK Health Security Agency recorded 1,504 heat-associated deaths during summer 2025, roughly half the 3,039 deaths its models had predicted for the period.

Summer 2025 was the warmest on record in the United Kingdom, with a mean temperature of 16.1 degrees Celsius. The previous record of 15.76 degrees was set in 2018.

Four separate heatwaves struck between June and August 2025. Peak temperatures approached 36 degrees Celsius. Nine days exceeded 32 degrees.

Dr Agostinho Sousa, head of extreme events at UKHSA, said the data "suggests that the actions taken across the health and care system may be helping to reduce harm" from heat exposure.

Fewer deaths than 1976

Summer 1976 remains the benchmark for prolonged UK heat. That year produced 16 days exceeding 32 degrees Celsius. Summer 2025 recorded nine such days, with shorter but more intense heatwave periods.

UKHSA's modelling uses historical mortality data, population demographics, and temperature forecasts to estimate expected excess deaths during heat episodes. The 3,039 prediction for summer 2025 was calibrated against those historical patterns.

The 50 percent gap between predicted and actual deaths marked the largest overestimation in UKHSA's heat surveillance programme since its current methodology was adopted in 2019.

What drove the temperatures

Met Office analysis attributed the record temperatures to three factors: persistent high-pressure systems over the British Isles, warmer-than-average sea surface temperatures in the North Atlantic, and dry spring soils that reduced evaporative cooling across England and Wales.

North Atlantic sea surface temperatures ran 1.2 degrees Celsius above the 1991-2020 average during June and July 2025. The Met Office said the warm seas amplified onshore air temperatures along the south and east coasts of England, where the highest readings were concentrated.

Earlier warnings, earlier action

UKHSA credited three factors for the lower-than-expected death toll: earlier adoption of protective behaviours by the public, improved heat health alerts issued to NHS trusts and care homes, and targeted interventions for high-risk populations.

Dr Sousa said heat health alerts triggered responses across the NHS, including welfare checks on elderly patients, adjusted medication schedules for people taking diuretics and beta-blockers, and extended opening hours at cooling centres in 47 local authority areas.

"We have seen that people are responding to heat health alerts earlier in the season," Dr Sousa said. "The behavioural changes, combined with actions by GPs, care homes, and hospitals, appear to have made a measurable difference."

Who remains at risk

UKHSA data showed the highest mortality rates among adults aged 75 and over, with that age group accounting for 78 percent of the 1,504 recorded deaths. Babies under one year old and people with pre-existing heart disease also faced elevated risk.

Dr Sousa said heat-related illness presents differently in older populations. "Older adults may not feel thirsty until they are already significantly dehydrated," he said. "They are also less likely to recognise the early signs of heat exhaustion."

England's care home sector reported 312 heat-related incidents during summer 2025, down from 487 in summer 2022. The Care Quality Commission attributed the reduction to updated guidance issued in March 2025 requiring all residential facilities to have documented heat action plans.

The 2026 outlook

Global temperatures in 2026 are expected to reach 1.46 degrees Celsius above pre-industrial levels, according to the World Meteorological Organisation. WMO has classified 2026 as likely to rank among the four warmest years on record.

Met Office seasonal forecasts issued in March 2026 gave a 60 percent probability that summer 2026 temperatures in the UK will exceed the 1991-2020 average. The agency has not yet predicted whether 2026 will break the records set in 2025.

UKHSA said it will publish updated heat health alert thresholds in May 2026, calibrated against the 2025 data. Dr Sousa said the agency is reviewing whether current alert levels need to be lowered to trigger earlier responses in future seasons.