The UK's record-breaking June heatwave has reached a boiling point, with temperatures feeling more sweltering than the previous peak in July 2022. But what makes this heat so unbearable? The answer lies not just in the thermometer readings, but in the humidity levels that are making the air feel like a sauna.
According to the Met Office, the dew point temperature – a key indicator of moisture in the air – is currently in the low 20s Celsius. This is a stark contrast to the single-figure dew points recorded during the July 2022 heatwave, which was characterised by very dry air. The Royal Meteorological Society (RMS) explains that while 2022's extreme heat was dry and intense, the present heatwave is notably moist – making even moderate temperatures feel like a furnace.
The combination of high heat and humidity poses significant health risks. The RMS highlights that the body cools itself primarily through sweating; however, if the surrounding air is already saturated with moisture, sweat cannot evaporate effectively. This impairs the body's natural cooling mechanism, leading to a rise in core body temperature – especially during the night when temperatures stay above 20C, a phenomenon known as 'tropical nights'.
This high-pressure system, which originated in the warm and humid subtropics and passed over France before settling over the UK, is creating a 'heat-dome' effect. Experts link the increasing frequency and intensity of such heatwaves, along with higher humidity, to climate change. For every 1C rise in atmospheric temperature, the air can hold approximately 7% more moisture – making modern heatwaves feel more oppressive and dangerous.
To cope with these challenging conditions, individuals are advised to limit exposure during the hottest parts of the day (typically late morning to early evening) and seek shade or cooler environments. Dr Heather Massey, an associate professor at the University of Portsmouth specialising in extreme environments, also recommends keeping indoor spaces as cool as possible and staying well-hydrated by drinking plenty of fluids – especially for vulnerable groups such as the elderly and young children.