The Silent Killer

UK Heatwaves

It starts with something as seemly harmless as a hot, sunny day.

In the UK, the Met Office declares hot, sunny weather to be a heatwave when the daily temperature meets or exceeds a certain threshold for at least three days.

There are four heatwave thresholds in the UK reflecting the differences in our climate. The lowest is 25C (covering Wales and Scotland) and the highest is 28C (covering London and parts of the East Midlands).

Exceeding these temperatures may not appear potentially dangerous – until you look at the shocking data from the Office for National Statistics. The ONS estimates that the hot weather of 2022 was a factor in more than 4,500 heat-related deaths in England alone.

Summer 2025 has already seen higher average temperatures than the same period three years ago. The fourth summer heatwave is forecast this week, with temperatures climbing over 30C.

Unlike catastrophic floods and terrible winter storms, extreme heat is a silent killer. It is disproportionately lethal and often goes unnoticed until it’s too late.

Increases in heat-related deaths are not just a consequence of rising temperatures. They are exacerbated by our poorly-insulated homes; by the heat trap caused by the urban heat island effect in our towns and cities; by how we care for the vulnerable and address social inequality.

The extreme 40C temperatures recorded in the UK in summer 2022 were made 10 times more likely by climate change, according to research studies. While we can’t prevent the occurrence of future heatwaves we can reduce their severity by reducing the greenhouse gas emissions that fuel them.

There’s also a lot we can do to prepare for heatwaves. Extreme heat does not have to claim so many lives. But the increasing frequency, intensity and duration of heatwaves in the UK are sending a loud alarm that we need to take more action now to reduce their harshness and protect ourselves.