The UK is sweltering through an extreme heatwave, with temperatures forecast to reach 35°C in Manchester and 36°C in London on Friday (June 26) as health officials warn of growing pressure on emergency services. Rare red heat warnings remain in place after Thursday (June 25) provisionally became the UK's hottest June day on record, with 36.7°C recorded in Merryfield, Somerset. Hospitals have declared critical incidents, schools have closed, and a hosepipe ban has been introduced in parts of England. Despite similar temperatures being common in countries like Spain, Greece, and Italy, many people say the heat feels much harder to cope with in Britain.
Humidity Makes Heat Feel Worse
One of the biggest reasons this week's heatwave feels so unbearable is the unusually high humidity, which determines how effectively our bodies can cool themselves. Normally, sweating cools the body because moisture evaporates from the skin. But when there's already a lot of moisture in the air, sweat evaporates much more slowly, making it harder to lose heat. The Met Office says this week's air mass has travelled over the Atlantic before reaching the UK, meaning it contains much more moisture than during some previous heatwaves. Forecasters explained in a blog post: "Higher moisture levels increase dew point temperatures, which in turn make it more difficult for the body to cool itself through sweating. As a result, even if temperatures are similar to previous hot spells, the added humidity can make conditions feel more oppressive and increase the potential for heat-related impacts."
The geography of the UK also plays a role. Britain is surrounded by the sea and sits on the edge of the North Atlantic, so it is regularly exposed to moist air, according to experts writing for The Conversation. A 35°C day in Madrid may have relative humidity of around 20 per cent, while London could easily exceed 40 per cent, leaving far more moisture in the air and making conditions feel significantly more uncomfortable, they added.
A Different Type of Heatwave
This week's heatwave is also being fuelled by a weather pattern known as a heat dome, which wasn't seen during the hot spell recorded in May. University of Reading senior research scientist Dr Akshay Deoras told the BBC the heat dome is the "driving force" behind the current conditions. Unlike the UK's heatwave last month, when the centre of the heat dome sat directly over Britain, this week's system has been centred further south over France. This has drawn exceptionally hot and humid air northwards into the UK.
Those Relentless Tropical Nights
The Met Office said "tropical nights" — when temperatures stay above 20°C overnight — have been recorded across parts of England and Wales this week, making the heat feel relentless. Forecasters said: "These warm nights are a direct result of the high humidity and persistent air mass. Without sufficient cooling overnight, buildings retain heat, increasing discomfort and placing additional strain on vulnerable individuals. Sustained warmth, both day and night, is a key reason why warnings are issued. It reduces the opportunity for recovery and contributes to heat stress over multiple days." When nights remain hot, both homes and the human body have little opportunity to cool down before the next day's high temperatures arrive, which experts warn contributes to heat stress.
Britain Is Built to Keep Heat In
Homes across the UK were largely built to cope with cold winters rather than summer heat. Unlike many homes in southern Europe, air conditioning remains rare in the UK, while many buildings trap warmth inside. Mark Apsey, Honorary Professor of Engineering at the University of Exeter and Past President of the Institution of Chemical Engineers, said: "The UK's built environment was designed to retain heat in winter, not reject it in summer. That is the core engineering problem this heatwave exposes. Our homes suffer high solar heat gain through glazing, with little external shading to prevent it, limited ability to ventilate and purge heat safely overnight, and almost no mechanical cooling to remove the heat that builds up."
He added: "This event is more demanding than the daytime peak alone suggests. The risk is driven by sustained heat, high humidity and overnight temperatures that stay high. Buildings shed heat at night by losing it to cooler outside air. When nights stay above 20°C, as forecast here, that overnight cooling largely stops, so homes settle into a hot daily cycle with little recovery between days, rather than returning to a safe baseline each night. Combined with high daytime solar gain through unshaded glazing, indoor temperatures can stabilise at a level that is dangerous to vulnerable people, and the human body gets no overnight relief. That is why night-time temperatures and duration matter as much as the headline figure, and it is where our housing stock is most exposed."
Dr Laurence Wainwright, Senior Departmental Lecturer in the School of Geography and the Environment and Senior Researcher in the Department of Psychiatry at the University of Oxford, said: "The current heatwave has utterly exposed the unpreparedness of the UK to deal with high temperatures. Perhaps nowhere more has this been felt than in our schools. It is a travesty that any school in the UK should have to close entirely, or significantly reduce operating hours, because of heat. The situation we find ourselves in now is highly predictable and could have been prevented with proper action and infrastructure investment from the Government." He added that fewer than five per cent of school classrooms across Britain have air conditioning, despite heatwaves becoming increasingly common. Combined with humid air, tropical nights, and buildings that trap heat, experts say these factors help explain why temperatures in the mid-30s can feel far more unbearable here than they do in many popular holiday destinations.
