Output at work begins to plummet when temperatures hit the mid-30s. With Britain’s thermometers rocketing again, what chance is there of meeting your deadline?
It’s mid-morning in South Manchester and already 25C. Often crudely monikered the Rainy City, the fact of the matter is northern England’s largest urban sprawl clocks in with 15 days less wet weather than the national average. And in a study of all built up areas in the country, it only ranked 15th wettest.
This doesn’t account for damp or humidity, of course. Historically, Greater Manchester’s dominant role in the global cotton trade developed as a result of ideal climate conditions for storing the raw material. Specifically, the level of moisture in the air.
Skip forward more than a century and the environmental backdrop is changing rapidly. Today, the city will likely hit 30C, and up to 60% humidity. Over the coming days heat will potentially exceed 33C, humidity edging towards 67%.
Putting things into perspective, the UK rail network is pre-stressed with an average summer temperature of 27C. When conditions exceed this for sustained periods of time, infrastructure buckles, delays mount, and journeys are cancelled.
Until relatively recently, though, our understanding of how extreme heat impacts the people who actually do make it into work was limited. Then in 2022 — the year Greater Manchester smashed its all-time temperature records at 37.2C — Loughborough University published the first study of heat stress and productivity.
According to lead academic Professor George Havenith, Director of the institution’s Environmental Ergonomic Research Centre and a member of the international HEAT-SHIELD project, the effects are profound. In environments where thermometers surpass 35C, there is an average 35% fall in work rate. At 40C, the drop is 70%. Although the reality for most office jobs is air conditioning and climate control systems, many people employed in hospitality, events, construction and public transport are likely to endure much higher temperatures.
‘These findings enhance our current understanding of the consequences of extended occupational heat exposure and provide evidence that can be used to more accurately predict the socio-economic burden of future extreme heat,’ says Professor Havenith. ‘A significant drop in productivity will have a significant impact on employee welfare and business output. It is yet further evidence of why action should be taken now to stop global warming, the effect of which is already being felt hardest by those in the Global South.’
In May 2026, just as Britain found itself in the year’s first heatwave, Instaprint shared the results of a survey involving 2,000 UK workers. 71% believed high temperatures were making them less productive. 43% said they had observed a significant drop in output. 52% admitted to switching to ‘low-effort’ tasks such a emails and admin when the celsius count was unusually high. Mornings were less of an issue than the afternoon, with 68% pointing to a post-2PM slump in hot weather, and one-in-five confessing to sleeping at work to cope with the climate.
The UK currently has no legal upper limit for workplace temperatures, although there is now a concerted campaign to change this (it does, however, have regulations on low temperatures). Crucially, though, if new rules are introduced, it will likely not cover people who work from home, where air conditioning and other equipment suitable to cope with prolonged periods of high heat is less commonplace.
Humidity is an interlinked, but additional risk factor. When combined with heat, this is what’s known as the wet bulb temperature. When this hits 35C, even a healthy human cannot cool themselves down effectively, regardless of how much water they drink. For this to happen, conditions need to be a minimum 40C temperature, with 75% humidity or over. Currently, Britain is still some way off this mark, but 2026 has already seen widespread deaths in India as a result of the deadly phenomena. And Regius Professor Hannal Cloke, at the University of Reading, notes that compared with 2022’s record-breaking heatwave, conditions in Britain are already notably worsening in this context.
‘During the 2022 heatwave, which set the UK’s all-time temperature record, conditions in Reading on the peak day at 10am were very dry, around 28% humidity at 32 degrees,’ she explains. ‘[Late June’s] forecast [combined] temperatures at 10am of around 30°C with humidity closer to 50%, which produces a considerably higher wet bulb reading. In practical terms, that means the body has to work harder to cope despite the air temperature being somewhat lower than in 2022.’
Image: Igor Omilaev / Unsplash
More on heatwaves:
5 years of climate-related health and economic stress following early heatwave
After the heatwaves, it’s time to make UK workplaces climate resilient