What is a heat dome? Why Europe is sweltering under record-breaking May temperatures

Europe is bracing for more scorching temperatures this week following a weekend of record-breaking May heat that swept across parts of the continent.

Forecasters over at Severe Weather Europe warn that temperatures are soaring by 12-16°C above “long-term climatological norms” as greenhouse gases continue to fry the planet.

Southern and southwestern regions including Portugal, Spain and France are set to swelter under daytime highs of 38°C, with huge parts of France being placed under a moderate high temperature warning. Northern countries such as Germany and the UK are witnessing maximum temperatures exceeding 30°C.

France’s Météo-France weather agency blames a “heat dome” for the unusually high temperatures, with Severe Weather Europe agreeing that a “highly anomalous and powerful heat dome” has parked over Western and Central Europe.

“Air mass will be even hotter in the coming days for many countries, as the Heat Dome aloft intensifies further,” the weather forecaster says. “Because this pattern restricts vertical mixing and cloud cover, maximum and minimum temperatures alike will challenge historical monthly records across hundreds of stations in Western Europe.”

What is a heat dome?

Otherwise known as a ‘heat bubble’, the term heat dome wasn’t really popularised until 2010s. It has since been victim to the tabloidisation of weather phenomena – alongside other frequently sensationalised terms like ‘polar vortex’ and ‘snow bomb’ – meaning many people think it is simply synonymous with a heatwave, or several days of high temperatures.

Heat domes form when a high-pressure system develops in the upper atmosphere, causing the air below it to sink and compress – raising temperatures in the lower atmosphere. But because hot air expands, it creates a bulging dome that traps heat within it.

Winds are normally able to move high pressure around, but due to how far heat domes stretch into the atmosphere, the weather system becomes almost stationary.

Heat domes therefore lead to temperatures consistently soaring well above what is normal, drying out the ground and increasing the chance of wildfires.

A 2025 study published in Proceedings of the National Academy of Sciences found that atmospheric patterns that lock in extreme weather, such as heat domes and flooding, have nearly tripled since the 1950s due to human-driven climate change.

Are heatwaves and heat domes the same?

The UK’s Met Office defines a heatwave as an “extended period of hot weather relative to the expected conditions of the area at that time of year, which may be accompanied by high humidity”.

So, even if you experience multiple days of high temperatures – you aren’t necessarily witnessing a heatwave.

This also means that heatwaves and heat domes aren’t the same, but that heat domes can often cause a heatwave to occur due to trapping heat and raising temperatures.

Are May heatwaves becoming the ‘new normal’?

According to the EU’s Copernicus Climate Change Service (C3S), 2025 was the third-hottest year on record, both globally and in Europe. The past three years – 2024, 2023 and 2025, in that order – were the hottest ever recorded globally.

Last year, temperatures exceeded 40°C in dozens of nations, pushing countries into drought, igniting wildfires, and killing thousands. Researchers at Imperial College London and the London School of Hygiene & Tropical Medicine looked at 854 European cities and found that climate change was responsible for 68 per cent of the 24,400 estimated heat deaths last summer, having raised temperatures by up to 3.6°C.

The countries hardest hit by a single heatwave were Romania, Bulgaria, Greece and Cyprus, where from 21 to 27 July an estimated 950 heat deaths occurred in temperatures up to 6°C above average. That is around 11 daily deaths per million people.

But Ioanna Vergini of WFY24, a weather forecaster, tells Euronews Earth that the European summer isn’t just getting hotter – it’s getting longer at both ends.

“What we used to call a July phenomenon is now arriving in mid-May,” she warns.

“Climate attribution studies estimate that June heatwaves in Europe are around 10 times more likely today than they were in pre-industrial conditions, and the same trajectory is becoming visible for May."