What makes a ‘heat dome’ and what does it mean?

These unbearably hot and humid summer months that put millions of people across the globe at risk are typically made possible by phenomena known as

Heat domes can make already-high temperatures even more extreme and prolonged, and they are worsening in severity and becoming more frequent as the planet warms.

Here’s what to know.

What makes up a heat dome, and what does it do?

Heat domes are essentially high-pressure systems hovering above a region that trap heat and humidity, experts say.

They result from the northward flow of warm air. That system sends air sinking, pressure increasing and temperatures rising.

鈥淭he concept of a heat dome really means that the air in this region is so warm, and we know that warm air expands,” said Jennifer Francis, a climate scientist at the Woodwell Climate Research Center. “It basically means that the layers of the atmosphere are bulging upward as well.鈥�

Simply put, heat domes cause heat waves. They鈥檙e associated with very dry, sunny conditions that last for multiple days at a time, trap heat at the surface and help to amplify it, said Zachary Labe, climate scientist at Climate Central, an independent collective of scientists.

How has heat affected the world this year?

Heat impacted various regions of the world .

The its most abnormally hot month in 132 years of records in March, with first in the Southwest and then . Heat and in May. Extreme heat has since across the U.S., Canada and Mexico.

Starting mid-June, Europe has baked under unseasonable highs of around (104 Fahrenheit) in many places due to a heat dome.

Now, much of the by a long heat wave in the coming days, and already, much of the Southwest is experiencing temperatures around 100 degrees Fahrenheit (38 Celsius) this week and those temperatures could reach elsewhere by the Fourth of July holiday.

What role does climate change play?

Science shows that as the planet warms 鈥� the result of humans burning coal, oil and gas 鈥� heat waves get worse, last longer and become more frequent.

鈥淗eat waves like this are so directly connected to the climate crisis and climate change,鈥� Francis said, “and it鈥檚 because of how we鈥檝e been burning fossil fuels and cutting down forests for so long and increasing the concentration of heat-trapping gasses in the atmosphere.

鈥淭hese kinds of heat waves and droughts and associated fires are all increasing just as we would expect them to in a warming world,鈥� she said.

How can I stay safe?

Experts say people need to stay hydrated when sweltering heat and humidity hit.

Be sure to avoid outdoor exercise in the heat of the day 鈥� and find shade, or if you can, access to air conditioning. Some cities offer resources and cooling centers to provide relief.

Cooling off in nearby pools or bodies of water can also help.

Heat domes can make it difficult to fully recover from high temperatures at night, so finding ways to stay cool during the day and evening hours are important.

鈥淚t鈥檚 those night times 鈥� especially, locations and people, who don鈥檛 have access to adequate cooling, really need to be aware of the impacts that added heat stress will have and their body鈥檚 ability not to be able to cool down,” Labe said, “because humidity is going to be a really key factor in boosting those heat impacts.鈥�

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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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