If people feel they are suffering more than usual in the latest heatwave, it is not their imagination. Not only has the June temperature record in the UK been broken, but humidity is also relatively high, causing a temperature of 35C to feel like 41C.
What are science authorities saying about humidity this week?
“Humidity is unusually high at the moment,” says a Met Office spokesperson. Dew point temperature, which essentially indicates how much moisture is in the air, is “in the low 20s [centigrade] for this heatwave”, a far jump from the “single figures of the July 2022 heatwave”.
The Royal Meteorological Society (RMS) adds: “Back in July 2022, when we broke the 40C barrier for the first time, the air was very dry. In this current June 2026 heatwave, it is very moist. And that means even if the number on the thermometer isn’t as high, it will feel much worse, especially at night. If we can’t cool down overnight, the risk of dehydration, heatstroke and death rises, especially in the elderly and very young.”
The UK is experiencing an increase in tropical nights, where temperatures remain above 20C all night, as well as more extreme daytime temperatures.
What are the health risks posed by humidity?
“Hot and humid weather puts more stress on the body than hot and dry air,” says the RMS spokesperson. “We cool down by sweating, but if the air is already very moist there is nowhere for our sweat to go, and that means we can’t cool down and our core temperature will rise.”
Humidity has an important influence on human and animal health as well as on the weather and climate. This has been apparent at the World Cup, where the more humid venues, such as Miami, pose the greatest physical challenges to players.
The extent of the risk depends on the level of relative humidity, which is measured by the amount of water vapour that is in the air compared with the amount needed to saturate it.
Why does humidity make such a difference to the heat experience?
According to the RMS, “we tend to talk about air temperatures during heatwaves, but that doesn’t tell the full story. Air temperatures are measured in the shade for one thing, so it’s much warmer in direct sunlight. A better indication of how it will feel in a heatwave is to look at the dew point temperature, the wet bulb temperature or the heat stress index. These all take heat and humidity into account.”
Levels of humidity can influence how temperatures develop through the day, but have their biggest impact on how we feel the weather, rather than the temperature itself. Higher humidity is what creates that muggy, oppressive feeling people have been experiencing these last couple of days.
Is climate crisis associated with high levels of humidity?
Yes. Fossil fuels, such as gas, oil and coal, are heating the planet. And for every 1C warmer the atmosphere becomes, it is able to store 7% more moisture. This rise in water vapour is why modern heatwaves feel much more oppressive and can prove more dangerous. The effect varies from region to region. But the UK and other parts of northern Europe are among the most affected areas.
Climate breakdown is also making heatwaves more frequent and intense. The latest one in the UK is a high-pressure system that originated in the warm and humid subtropics before passing over France, where temperatures moved above 40C. It has been stuck above the UK for several days, causing a “heat-dome” effect as it cooks the air and ground below.
How can you best cope with the high heat and humidity?
Dr Heather Massey, an associate professor in extreme environments and physiology at the University of Portsmouth, says: “People can stay cooler during hot weather by limiting exposure to the hottest parts of the day, typically between late morning and early evening, and by seeking shade or air-conditioned environments whenever possible.
“Keeping indoor spaces cool by closing curtains or blinds during the day and opening windows at night can help reduce heat buildup. Wearing loose, light-coloured clothing made from breathable fabrics such as cotton can improve heat loss. Taking cool showers or baths, using damp cloths on the skin, spraying the body with water and staying in front of a fan or placing the hands and or feet in a basin of cold water can also help lower body temperature.”
Massey also advises drinking fluids regularly throughout the day, even if you are not feeling thirsty, to replace water lost through sweating.