How a heat dome is formed and why experts blame one for Europe’s baking temperatures

under an early heat wave this week, with millions of people experiencing extremely high temperatures, and experts say a phenomenon known as a heat dome is to blame.

Here’s what to know.

What is a heat dome?

that remain stationary for a few days, trapping dangerous heat and humidity, said Mireia Ginesta, a research associate at the Climate Litigation Lab at the Smith School of Enterprise and the Environment.

Heat domes result from a northward bulge in the jet stream 鈥� a river of fast-moving wind at high elevations 鈥� that creates the weather we experience.

鈥淗igh-pressure system means that the air is sinking, and as the air goes down to lower altitudes, it becomes compressed,鈥� Ginesta said. 鈥淪o the pressure increases and the temperature also increases.鈥�

How does a heat dome play a role in heat waves?

Those 鈥渂ulges鈥� are what set up the conditions that lead to a heat wave, said Jennifer Francis, a climate scientist at the Woodwell Climate Research Center.

鈥淭he heat dome is really what the jet stream is doing,鈥� Francis said. 鈥淭he heat wave is what we feel at the surface.鈥�

What is happening in Europe this week?

Millions of people across the continent have been experiencing exceptionally high temperatures as an early summer heat wave sears France, Italy, Spain and the United Kingdom.

鈥淚n Europe, they鈥檙e just not used to this,鈥� Francis said. 鈥淚t鈥檚 really just in the last decade or two where these sorts of really brutal heat waves have been happening and killing a lot of people because they don鈥檛 have the means to stay cool.鈥�

France, which has been the most affected so far, doesn’t have widespread air conditioning, and about half the country has been placed under a red heat wave alert by the national weather service. The nation has also reported around 40 fatalities because of drowning, as people sought cooling relief.

Those conditions are expected to last for several days, with temperatures as high as 104 degrees Fahrenheit (40 degrees Celsius).

鈥淲e are going to see the June temperature records not just broken, but completely annihilated,鈥� said Liz Bentley, chief executive at the Royal Meteorological Society and a professor of meteorology at the University of Reading.

How is climate change influencing these phenomena?

is making the conditions for heat domes happen more often, experts say. And are being impacted.

鈥淲e鈥檙e warming the globe and that means we鈥檙e shifting the range of temperatures that any given place experiences,鈥� Francis said. 鈥淎nd as you shift that range of temperature, you鈥檙e making the extreme temperatures much more likely.鈥�

Effectively, the world has turned up the thermostat temperature, Bentley said.

鈥淐limate change is definitely having an impact on the fact that they鈥檙e more frequent, they鈥檙e more intense, and they鈥檙e more persistent as well,鈥� Bentley said of heat waves. 鈥淭hey hang around a lot longer than they used to do.鈥�

How can people stay safe?

It is important that people experiencing these extreme temperatures hydrate, avoid exercise in the heat of the day, find shade and safely cool off in nearby streams, lakes or even the ocean if they have access.

In France, for instance, have been canceled, and authorities are restricting public alcohol drinking.

鈥淥ne of the biggest problems is the nighttime heat,鈥� Francis said. 鈥淚f you don鈥檛 give your body a chance to cool off at night, it just starts to accumulate in your body and that can really start to affect your health. And so figuring out a way to stay cooler at night is very, very important.鈥�

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Associated Press video journalist Havovi Todd in London contributed to this report.

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Alexa St. John is an Associated Press climate reporter. Follow her on X: . Reach her at ast.john@ap.org.

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