Millions of people across Europe are enduring dangerously high temperatures this week as an early summer heat wave takes hold, and climate scientists say a weather phenomenon called a heat dome is responsible.
So what exactly is a heat dome? According to Mireia Ginesta, a research associate at the Climate Litigation Lab at the Smith School of Enterprise and the Environment, heat domes are high pressure systems that stall in place for several days, locking in dangerous levels of heat and humidity.
These events are triggered by a northward bulge in the jet stream — the band of fast-moving winds high in the atmosphere that drives much of our weather.
“High pressure system means that the air is sinking, and as the air goes down to lower altitudes, it becomes compressed,” Ginesta explained. “So the pressure increases and the temperature also increases.”
Jennifer Francis, a climate scientist at the Woodwell Climate Research Center, described it this way: “The heat dome is really what the jet stream is doing. The heat wave is what we feel at the surface.” She added that those northward bulges in the jet stream are what create the conditions leading to extreme heat events.
France, Italy, Spain, and the United Kingdom are among the nations being hit hardest by the current heat wave. France has been the most severely affected, with roughly half the country placed under a red heat wave alert by its national weather service. The country lacks widespread air conditioning, and approximately 40 deaths linked to drowning have been reported as people sought ways to cool off. Temperatures are expected to reach as high as 104 degrees Fahrenheit (40 degrees Celsius) and remain elevated for several days.
“In Europe, they’re just not used to this,” Francis said. “It’s 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’t have the means to stay cool.”
Liz Bentley, chief executive at the Royal Meteorological Society and a professor of meteorology at the University of Reading, warned that temperature records are in serious jeopardy. “We are going to see the June temperature records not just broken, but completely annihilated,” she said.
Experts are pointing to climate change as the driving force behind the increasing frequency of heat domes worldwide. Francis noted that as global temperatures rise, extreme heat becomes far more likely everywhere. “We’re warming the globe and that means we’re shifting the range of temperatures that any given place experiences,” she said. “And as you shift that range of temperature, you’re making the extreme temperatures much more likely.”
Bentley agreed, saying climate change is making these events worse in every way. “Climate change is definitely having an impact on the fact that they’re more frequent, they’re more intense, and they’re more persistent as well,” she said. “They hang around a lot longer than they used to do.”
Francis also highlighted a danger that many people overlook — the heat at night. “One of the biggest problems is the nighttime heat,” she said. “If you don’t 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.”
Authorities in France have responded by canceling trains, concerts, and sporting events, and have placed restrictions on public alcohol consumption. Health officials are urging anyone facing extreme heat to stay hydrated, avoid physical activity during the hottest parts of the day, seek shade, and cool off safely in nearby bodies of water when possible.
