In May 2026, parts of the UK officially entered a heatwave, with a record spring temperature of 35.1 °C in Kew Gardens, London. As the climate warms, heatwaves will become more frequent in the UK.

What are heatwaves?

A heatwave is defined as three consecutive days where daily maximum temperatures meet or exceed a specific threshold. The Met Office sets the technical thresholds for a heatwave in different parts of the UK:

  • 25°C: Scotland, Northern Ireland, northern England, Wales, south-west England
  • 26°C to 28°C: central and south-east England

How do heatwaves happen?

Heatwaves are most common in summer when high pressure systems develop, leading to more settled weather conditions; high pressure systems are caused by air from higher in the atmosphere sinking to the surface, and this air tends to be drier, leading to fewer clouds and less precipitation. High pressure systems are slow moving and can persist over an area for a long time: such as days or weeks. The jet stream, a strong core of wind in the earth’s atmosphere, is usually to the north of the UK in the summer, which enables high pressure to develop over the country, resulting in longer periods of dry, settled weather.

Warmer air often travels up to the UK from southern Europe and Africa. However, parcels of air can also travel from more northerly regions, such as Greenland, and as these parcels descend, they become compressed, which causes them to warm up (a process known as adiabatic warming) at a rate of up to 10°C per kilometre of descent. This has been a feature of many recent heatwaves..

Heatwaves are extreme weather events, but research shows that climate change is making them more likely. As the climate warms, by 2050 the UK will see higher temperatures and more frequent weather extremes, such as heatwaves.

Summer 2018 and summer 2006, were the joint hottest summers on record. Summer 2022 was the first time that the UK temperature exceeded 40°C, with a new record-high temperature for the UK was recorded of 40.3ºC in Coningsby, Lincolnshire. Spring 2025 was the warmest and sunniest on record, and there were four heatwaves declared in Summer 2025. So far, 2026 has provisionally recorded the hottest spring temperature on record.

What are the impacts of heatwaves?

Heatwaves pose risks to infrastructure, the environment and health.

During the summer 2022 heatwave, many parts of the UK’s infrastructure system struggled, with rail tracks buckling and overhead power lines sagging in extreme heat. Power cuts are also more frequent, affecting multiple critical assets, including energy, IT and water infrastructure.

Heatwaves also have repercussions for plants and animal species, with warmer seasons altering phenology (biological cycles within nature). As these timings shift, so too do ecosystem dynamics, altering the growing seasons of plants with repercussions for food supply chains and loss of harvests.

Additionally, prolonged warmer weather can harm people’s health, leading to disrupted sleep and increased health risks for vulnerable groups such as older adults, children, and people with heart or lung problems. Following the June 2025 European heatwave, academic modelling suggests that climate change trebled the number of heat-related deaths.

More information on the UK’s plans and progress in adapting to climate change impacts, such as those from heatwaves, is set out in the Commons Library research briefing, Climate change adaptation and resilience in the UK.

Are heatwaves becoming more common?

Yes. Climate science finds that extreme weather events, such as heatwaves, are already becoming more frequent in all parts of the world. They are likely to become even more frequent for the UK.

Analysis from the Met Office has found that events such as the summer 2022 and 2025 heatwaves, with prolonged hot weather and long periods with no rainfall, are indicative of what the UK’s future climate could look like as a result of climate change.

About the author: Nuala Burnett is a senior researcher at the House of Commons Library specialising in Climate Change.

Photo by: whitcomberd, via Adobe Stock