Britain and Switzerland recorded their hottest days of June on Thursday as an intense early-summer heatwave swept across much of Western Europe, causing dozens of deaths, straining power systems, and forcing the closure of schools and popular tourist attractions.
While temperatures in Britain climbed to around 35°C, many parts of India regularly experience summer temperatures exceeding 45°C. Yet Britons often describe such heat as extremely uncomfortable, raising a common question: why does 35°C in the UK sometimes feel more oppressive than 45°C in India?
According to experts, the answer lies in a mix of humidity, building design, extended daylight hours, and the degree to which people are accustomed to hot weather.
Unlike southern Europe or many regions of India, Britain is surrounded by the Atlantic Ocean and several seas, resulting in air that often contains significantly more moisture. On hot days, cities such as London may experience relative humidity levels above 40%, whereas cities like Madrid can record similar temperatures with humidity closer to 20%.
This higher moisture content has a major impact on how heat is perceived by the human body.
Sweating is the body's natural cooling system, but it only works effectively when sweat evaporates from the skin. In humid conditions, evaporation slows because the air is already saturated with moisture.
As a result, the body finds it harder to release excess heat, increasing the risk of dehydration, heat exhaustion, cardiovascular strain, and respiratory problems, even at temperatures lower than those commonly experienced in tropical regions.
Meteorologists use a measure known as wet-bulb temperature, which combines heat and humidity, to assess the level of heat stress on the human body.
During the current heatwave, wet-bulb temperatures in southern England are expected to approach 25°C. Although this remains below the theoretical survival limit, it is still high enough to pose health risks, particularly for older adults and vulnerable individuals.
In drier climates, air temperatures often need to exceed 40°C to create a comparable level of physiological stress.
However, humidity alone does not explain why British heat can feel so intense.
Britain’s housing stock was largely designed to retain warmth during cold and damp winters rather than cope with frequent heatwaves. Traditional brick houses, tiled roofs, and concrete apartment buildings absorb heat during the day and gradually release it overnight, effectively acting as what scientists call “thermal batteries.”
In addition, air conditioning remains uncommon in most British homes, unlike in many hotter countries where cooling systems are considered essential.
By comparison, countries such as India have adapted over generations to extreme summer temperatures. Many buildings feature thick walls, shaded courtyards, external sunshades, and natural ventilation systems that help keep indoor environments cooler.
Lifestyle patterns are also shaped around the climate, with outdoor work and travel often reduced during the hottest parts of the day.
The seasonal progression of heat differs as well.
In much of India, temperatures rise steadily throughout spring before reaching their peak in May and June, giving people, infrastructure, and health systems time to adjust.
Britain, on the other hand, often experiences sudden heatwaves following prolonged periods of cool and wet weather. This year, temperatures jumped from chilly nights and late frosts in May to record-breaking heat within a matter of weeks, leaving little opportunity for acclimatisation.
Another important factor is Britain’s exceptionally long summer daylight hours.
During June and July, daylight lasts well into the evening, allowing roads, buildings, and pavements to absorb solar energy for longer periods. Even after sunset, this stored heat continues to radiate back into the environment, keeping temperatures elevated overnight.
These “tropical nights,” where temperatures remain above 20°C, make it difficult for the body to recover from daytime heat exposure.
Cities are especially affected due to the urban heat island effect, where materials such as concrete and asphalt trap heat and release it slowly. High overnight humidity further reduces the body’s ability to cool itself.
As climate change contributes to more frequent and severe heatwaves across Europe, experts argue that Britain’s challenge is not simply rising temperatures. Rather, it is the mismatch between a warming climate and a country whose homes, infrastructure, and daily habits were developed for much cooler conditions.
This explains why a 31–35°C heatwave in Britain can often feel more exhausting and uncomfortable than a significantly hotter day in many parts of India, despite the lower temperature reading.
