Heat Stress Is Now a Leading Cause of Weather-Related Sick Leave

Britain has been through several heatwaves this summer, and heat stress is now among the biggest causes of weather-related sick leave. Very high temperatures produce heat rashes and cramps, and at the severe end exhaustion and heatstroke.

But a recent survey of workers in seven climate-exposed sectors shows that extreme weather affects health, wellbeing and productivity in the colder months too — a dimension largely missing from the public debate.

The gap in the official response

The Climate Change Committee, which advises the government, recently assessed the risks of a changing climate and what adaptation requires. Its report, and the wider adaptation debate, has largely overlooked workers.

In June the Health and Safety Executive issued a heat health alert urging employers to protect staff — without offering any guidance on what "too hot" actually means.

There is currently no law setting a maximum working temperature in the UK. Nor has there been a comprehensive analysis of the short- and long-term health effects of the 2022 heatwaves on British workers.

Extreme temperatures have forced some workers to take sick leave, with 40% of weather-related absences citing heat as a factor. Photograph: Dragon Images

How much the climate has already shifted

These effects follow from measurable change. The decade from 2015 to 2024 was 10% wetter and 1.24°C warmer than the 1961–1990 baseline. The past three years all rank among the five warmest on record, and the 40°C threshold was exceeded in July 2022 for the first time since the mid-19th century.

The economic consequences are substantial. There is no full estimate for the UK yet, but projections for climate-induced weather hazards more broadly — flood damage, infrastructure failure, falling productivity — point to a decline in GDP of between 3% and 7%, alongside indirect losses from reduced productivity, absenteeism and impaired performance.

What the survey found

The survey covered 1,288 workers across seven climate-exposed sectors. Heat stress emerged as one of the leading causes of weather-related sick leave: 40% of workers who had taken such leave cited heat as a factor.

But heat is only part of it. Workers reported being affected across a range of hazards including flooding, drought, storms, snow and ice, and conditions related to air pollution. The picture is of a workforce exposed year-round rather than for a few weeks each summer.

Crucially, many are already adapting informally — changing hours, taking unofficial breaks, modifying tasks — without adequate employer support or any policy framework recognising that they are doing it.

Why the absence of a threshold matters

The missing maximum temperature is not a technicality. Without one, the duty on employers is to take reasonable steps, which is unenforceable in practice because nobody has defined the trigger.

An employer acting in good faith has no benchmark. An employer acting in bad faith has no obligation. And a worker who believes conditions are unsafe has nothing to point to.

Setting a number is genuinely difficult — the tolerable temperature for an office differs from a foundry or a delivery van — which is why the issue has been deferred for years. But the alternative currently in force is a regulator issuing alerts that specify no action, to employers with no standard, on behalf of workers already taking sick leave in numbers that show up in the data.