As the UK experiences increasingly warmer summers, the phenomenon of tropical nights is becoming more relevant to both weather forecasting and public health.
A tropical night is defined as a night when the temperature does not fall below 20°C. While often associated with warmer climates, recent studies show that the UK is now seeing more frequent occurrences of these events, particularly during heatwaves.
In July 2022, the UK experienced three consecutive tropical nights, marking a significant milestone in the country’s climate history. This event was characterised by minimum temperatures remaining above 20°C for three successive 24-hour periods. Such conditions pose serious health risks, especially for vulnerable populations.
Just how high will temperatures get? 🌡️
— Met Office (@metoffice) June 18, 2025
Here's a look at when the peak temperatures may occur where you are over the next few days 📈 pic.twitter.com/wgnhRDnh2u
Health Impacts of Hot Nights
Tropical nights can have a profound impact on human health. The body relies on cooler nighttime temperatures to regulate core temperature and recover from daytime heat. When overnight temperatures remain elevated, this recovery process is disrupted, potentially leading to increased cardiovascular stress and sleep disturbances. Studies have shown that high nighttime temperatures are linked to increased mortality, particularly among older adults and those with pre-existing health conditions.
The Role of Climate Change
An attribution study by the Met Office found that the likelihood of experiencing three consecutive tropical nights during July has increased significantly due to climate change. In a pre-industrial climate, such an event had a probability of less than 1% per year. In today’s climate, that probability has risen to approximately 20% per year. This shift highlights the growing influence of anthropogenic factors on extreme weather events in the UK.
READ MORE: Met Office 10-Day Trend: Temperatures to peak this weekend
Climate projections suggest that tropical nights will become more frequent and intense. Under a high emissions scenario, the highest three-day minimum temperature observed each year is expected to rise steadily through the 21st century. This trend underscores the importance of adaptation strategies, particularly in urban areas where heat retention in buildings can exacerbate overnight temperatures.
Staying safe during tropical nights
The UK Health Security Agency already incorporates overnight temperatures into its heat-health alert service, recognising the role of tropical nights in public health outcomes. As the climate continues to change, it is essential to promote adaptive actions, such as improving building ventilation and supporting vulnerable communities.
Friday and Saturday nights will be warm and uncomfortable for sleeping, with temperatures perhaps staying above 20°C in places - known as a "tropical night" 🌡️
— Met Office (@metoffice) June 18, 2025
Whilst the next couple of nights won't generally be quite as warm, many places will stay in the mid teens Celsius 📈 pic.twitter.com/9ZyCR4Z39y
In summary, tropical nights are becoming less rare in the UK. Through continued research and public engagement, the Met Office aims to support resilience against the impacts of extreme heat and ensure communities are prepared for the challenges ahead.
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