The UK's summer nights are becoming increasingly tropical, with temperatures remaining above 20°C for the entire night. Once a rare occurrence in Britain, these warm nights are now more common, particularly in urban areas where built-up spaces absorb and retain heat like nowhere else.
This surge in tropical nights is linked to a combination of factors: the 'urban heat island' effect, which traps heat in cities; broader climate change patterns leading to warmer temperatures overall; and the way our countryside landscapes are being altered by human activity. The consequence is that city streets often stay significantly warmer than surrounding countryside, even after sunset.
The impact on people's lives goes far beyond just a bit of discomfort. Sustained high temperatures can disrupt sleep patterns, making existing health conditions like cardiovascular and respiratory illnesses worse for those who suffer from them. Vulnerable populations – the elderly, very young children, and those with pre-existing health issues – are particularly at risk during heatwaves.
For infrastructure, especially transport networks, elevated overnight temperatures also pose challenges: roads and railways retain heat, potentially affecting their integrity and requiring extra monitoring or maintenance; and increased demand for cooling systems like air conditioning puts a strain on energy grids.
As the UK sees warmer summers, the frequency of tropical nights is set to rise. This trend highlights the need for urban planning strategies that incorporate green spaces, reflective surfaces, and other measures designed to mitigate heat absorption in cities – and for public health campaigns advising people on how to stay cool and hydrated during heatwaves.