‘Heat dome’ effect: All about Europe’s killer heat wave and a warning for the US

As a “heat dome” wreaks havoc across Europe, with more than 1,300 excess deaths on the continent, France being the worst, the same weather phenomenon has been forecast for the US amid the FIFA World Cup, when millions of football lovers are camping across that country.

Europe has been grappling with what researchers call the worst heat wave ever recorded on the continent. France alone saw around 1,000 additional deaths last week, at the height of its heat wave. Temperature records were toppled in several European countries over the weekend, wildfires were sparked in Germany, and the Berlin police used water cannons to cool down the crowds.

The heat was so intense in Germany that the concrete of its famous highway, the Autobahn, burst in two places outside Berlin and had to be closed. Other highways were also reportedly damaged. France has recorded more than 70 drowning deaths alone, as people desperately tried to cool off.

So, why are two continents grappling with such deadly heat waves? Is it about El Nino? How much is climate change responsible? Here are some of these questions answered.

1. What is a heat dome effect, which is being blamed for the heat wave across Europe and now the US?

A heat dome occurs when a persistent high-pressure region traps hot air over a large area, acting like a lid on a pot. A heat dome forms when a strong ridge of high atmospheric pressure settles over a region. The high pressure pushes air down towards the ground. As the air sinks, it compresses, and compression causes the air to become much warmer.

This sinking air acts like a physical barrier or “lid”. It prevents the hot air near the ground from rising and escaping into the upper atmosphere. Because the air cannot rise, clouds cannot form. This leaves the sky completely clear, allowing the summer sun to beat down continuously and bake the ground day after day.

Also read: World's heat capital: Why India is becoming the hottest place on Earth

Heat domes are typically caused by a sluggish or distorted jet stream—a fast-flowing, narrow river of air located high up in the atmosphere. These powerful winds sit in the troposphere—about 8 to 15 kilometres above the Earth’s surface—and flow from west to east.

A wavy jet stream can create massive, slow-moving loops that trap weather systems in one place for days or even weeks. The intense, prolonged heat quickly dries out vegetation and soil, creating prime conditions for wildfires. Worst, the high-pressure system prevents the area from cooling down at night, offering no relief to ecosystems or humans without air conditioning.

2. Are heat domes uncommon in Europe and the US?

No, heat domes are, in fact, natural features of summer weather on both continents. But, they have become dramatically more frequent, severe, and long-lasting due to climate change.

Research indicates that the atmospheric patterns responsible for locking these heat domes in place have nearly tripled since the 1950s.While both regions experience them, the geographic frequency and how they manifest differ between the US and Europe.

In the US, heat domes are highly common seasonal fixtures, though their traditional boundaries are expanding. According to the New York Times, the Central Plains and the American Southwest are topographically and geographically the most prone to heat domes. Flat land away from large bodies of water allows massive high-pressure ridges to park easily.

But while historically restricted to the South and Midwest, heat domes are now frequently pushing into non-traditional zones, such as the major Pacific Northwest heat dome event in June 2021.

This week, a threatening heat dome has been forecast to engulf central and eastern US, including World Cup host cities such as Boston, Philadelphia and Kansas City, Missouri, all of which have open-air stadiums.

Also read: Monsoon no longer a respite: Study flags rising heat stress in rainy season

More alarmingly, meteorologists have been increasingly documenting “dual heat domes” in the US, where two separate massive high-pressure systems simultaneously trap heat over both the western and eastern halves of the country.

In Europe, high-pressure ridges are a normal part of summer, but extreme, stationary “heat domes” are relatively modern phenomena, escalating threat for the continent. Traditionally, heat domes are most common in Southern Europe (Spain, Italy, and Greece) due to hot air blowing north from Africa.

But now, heat domes are routinely shattering barriers to sit over Western and Northern Europe, resulting in unprecedented, multi-day spikes in areas like the UK, France, and Germany that completely lack the infrastructure to handle it.

Hundreds of people gather in a public pool in Frankfurt, Germany, last week. AP/PTI

3. Is El Nino responsible? Does climate change and global warming have any role to play?

No to the first question, and a big yes to the second.

A new study from the World Weather Attribution, a Europe-based collaboration of scientists, reported on Friday that the record-breaking heat and humidity in Europe would not have been possible without climate change. The rapid study found that the heat would have been virtually impossible just five decades ago, and is 200 times more likely today than it would have been 20 years ago.

According to climate scientists, Europe is warming at twice the global average rate, making the entire landmass acutely vulnerable to heat dome systems.

According to meteorologists at the University of Reading, two factors are making heat domes a regular summer crisis. One is called the “springboard effect”. Global warming has raised baseline temperatures. When a heat dome forms today, it starts from a hotter baseline, accelerating temperatures into the extreme zone much faster.

Also read: Why are Indian summers becoming unbearable? | Raghu Murtugudde interview

The second factor is the previously-mentioned jet stream. A warming Arctic has weakened the jet stream, creating a “wiggly” pattern. These atmospheric wiggles get stuck in place for weeks, causing high-pressure systems to stall and bake the earth below relentlessly.

World Health Organisation (WHO) Director-General Tedros Adhanom Ghebreyesus has already warned that Europe, as the fastest-warming continent, needs to do more to protect its citizens. Tedros wrote on X on Sunday (June 28). “Right now 150 million people are living under extreme heat, hundreds have died, schools are shut, grids are buckling.”

Driven by climate change and global warming, the “once-in-a-generation” heat wave is now occurring nearly every year, Tedros said.

4. Why is causing so many deaths in Europe?

While in tropical countries like India, people are asked to stay home during heat waves, home is simply not the safest refuge during a heat wave in Europe. For example, a sharp increase was reported in the deaths reported at private homes in France, especially in the Paris region, during the heat wave.

That’s because Europe is simply not used to such temperatures and its infrastructure was ever built keeping these heat waves in mind. As Tedros warned, “Heat stress is often called the ‘silent killer’ — and European homes, workplaces and schools were not built for these temperatures.”

Let’s take the example of Paris, often called the most beautiful city in the world, with its dreamy rooftops. Many of Paris’s buildings that look so picturesque from the outside proved to be dangerous for health during the unrelenting heat.

That was particularly true for those living in the attic, directly under the roofs—people who often cannot afford larger, lower-floor apartments less impacted by direct sun. Extreme heat can make these attics deadly.

A study of a record-breaking 2003 heat wave blamed for 15,000 heat-related deaths found that living in a Paris attic room directly under the roof increased the risk of death by more than fourfold, France’s public health agency said in a report last year.

And researchers who studied heat-related deaths in European cities for a study published in The Lancet Planetary Health journal in 2023 found that Paris had the highest risks of heat-related deaths out of 30 European capitals they looked at.

Also read: Heatwave effect can be cut by decongesting cities

About three-quarters of Paris rooftops use sheets of zinc as covering, producing the city’s magnificent grey vistas that have long inspired artists and filmmakers. Zinc is weather-resistant, malleable and can be recycled. But as a metal, it also absorbs and conducts heat.

It’s not only France though. The entire continent, barring the southern parts, was built for a cool climate. Centuries-old architectural designs across northern and western Europe rely heavily on thick brick or stone insulation, which is designed to lock winter heat inside the home. Crucially, most of these buildings lack external shutters or awnings, meaning solar radiation penetrates straight through glass windows, heating indoor air with no mechanism to exhaust it.

Even hospitals and nursing homes are turning into deadly furnaces. In the western German city of Dormagen, dozens of residents of a nursing home were evacuated for medical care due to dangerous heat conditions in the building. The local fire department reported that temperatures inside the home had reached 35 degrees Celsius.

And unlike the US, where 90 per cent homes are air-conditioned, only about 20 per cent of European homes have air conditioning. Some countries woke up to the crisis early, including Italy. Nearly 50 per cent of Italians are now air-conditioned, while 7 per cent of British homes now have AC. If you think the figure is insignificant, it is double what it was merely three years ago.

A Fiaker horse carriage rider cools his horses on a hot summer day in the city centre of Vienna, Austria, last week. AP/PTI

5. What about the rest of the infrastructure? Can it withstand heat?

No, as it has been seen, the unprecedented heat is causing extensive structural failures across multiple systems. European buildings, grids, and transit networks were engineered based on historical averages that rarely breached 30 degrees centigrade.

As a result, the concrete surface on countless highways in Germany shattered, and the national rail operator Deutsche Bahn issued a weekend warning to avoid all unnecessary train travel. More than 600 passengers had to be evacuated from an overheated train in Brandenburg after a tree fell onto an overhead power line during a storm on Saturday evening.

The train, which was on its way from Hamburg to Prague, lost power. The air conditioners stopped working and the doors were locked until emergency responders forced them open. Two people were hospitalised with heat-related problems.

Also read: Europe sizzles under record heatwave as France records 1,000 excess deaths

In the eastern city of Leipzig, trams were shut down due to heat damage to tracks and switches. The Leipzig Public Transportation Authority said the high temperatures had caused the joint sealant for asphalt and concrete in switches and tracks to run and clump together in many places.

Germany is also facing a peculiar problem of its own. In Gohrischheide, in eastern Germany, a fire broke out in a large forest that’s still contaminated with ammunition from World War II. In southwest Germany, too, near the village of Traisen, the heat sparked a forest fire in an area that also contained unexploded ordnance.

Firefighters had to stop work temporarily after explosions took place and an ordnance disposal unit was brought in to continuously assess the situation.

6. What kind of temperatures has Europe recorded and what is the outlook for the continent and the US?

The intense “heat dome” has shattered all-time records in Western Europe—breaching 43 degrees Celsius in France and 40 degrees in the UK and Spain. The system has moved east, placing Poland, Germany, Hungary, and the Czech Republic under severe heat warnings with temperatures peaking over 41 degrees.

In Germany, 41.7 degrees Celsius was recorded in Neißemunde, near the border with Poland. The latter baked under its new all-time high of 40.5 degrees Celsius. The Czech Republic experienced its hottest day ever with 41.9 degrees.

Unusually high temperatures were recorded even in the Nordic countries. Denmark recorded 37 degrees Celsius in Odum, north of Aarhus. In Switzerland, a record 38.8 degrees was recorded in the city of Basel.

Temporary relief is expected for Western Europe starting Friday (July 3), but the respite will be short-lived, as a second, potentially longer heat wave is forecast to build in early July.

As for the US, feeling the heat this week will be the East Coast cities of New York, Philadelphia, Washington and Baltimore and Midwestern and Great Lakes cities including Chicago, St. Louis and Detroit. Southern cities including Dallas, Little Rock, Arkansas, and Memphis, Tennessee, will also see high temperatures.

Also read: India under heat dome: Early April surge pushes many regions towards 40°C mark

The National Weather Service issued an extreme heat watch for Philadelphia and surrounding regions starting Wednesday afternoon and into Saturday evening, with dangerously hot “feels-like” temperatures, up to 43.3 degrees Celsius during the daytime.

An extreme heat warning is also in effect for Kansas City and other portions of west central Missouri until Friday night, with heat index values as high as 40.6 to 43.3 degrees expected. The New York City area could see near-record high temperatures of up to 42.8 degrees. The heat index in Boston and much of southern New England could skyrocket to 43.9 degrees.

7. What measures are being taken in Europe and the US for tourists and locals?

European governments have deployed emergency Heat-Health Action Plans to mitigate mass casualties, while the US and FIFA are implementing a tiered heat-mitigation model specifically tailored to handle millions of World Cup fans. Interventions are focused heavily on hydration, active cooling infrastructure, and restricting high-risk activities.

European cities have transformed public buildings into designated cooling havens. For instance, Barcelona has activated a network of over 500 climate shelters (libraries, pharmacies, and civic centres), while Amsterdam has established targeted “cool-down” zones complete with public water, seating, and pet accommodations in vulnerable districts.

Municipalities like Paris have activated emergency phone trees and house-call rosters to conduct physical welfare checks on isolated elderly and high-risk residents.

In Italy and parts of Southern Europe, governments have legally banned outdoor labour (such as construction and agricultural work) during peak afternoon heat, utilizing state furlough funds so labourers do not lose income.

To prevent dehydration and take pressure off emergency medical services, Paris restricted public daytime alcohol sales. Other cities have cancelled mass outdoor festivals, sports events, and pride marches.

Also read: Three-fourth of India's population at 'high' to 'very high' heat risk: CEEW study

The Eiffel Tower and other Paris venues set up misting stations to cool crowds. The government ordered organisers of music day events to limit alcohol use to “preserve emergency services and allow medics to concentrate on taking care of the most vulnerable.”

Berlin police found a unique way to help suffering citizens and tourists alike. They put up two huge water cannons — usually used to disperse unruly protesters — in front of the iconic Brandenburg Gate and sprayed the cool water across the cheering crowd.

Multiple school districts across the Netherlands and Germany have shortened the school day or reduced lesson counts to dismiss children before classrooms reach dangerous temperatures.

In the US, with 14 of the 16 host venues under threat, tournament organizers are using a “tiered heat mitigation model” to safeguard international and domestic travellers. Four primary venues—Dallas, Houston, Atlanta, and Los Angeles—are utilizing fully enclosed or passive structural air-conditioning to drop indoor temperatures.

Standard venue safety rules have been waived; spectators are officially allowed to bring factory-sealed water bottles into stadiums. Venues have built expanded water-refill stations too. Open-air venues have deployed fleet line cooling buses, high-velocity misting tents, and designated shaded fan zones outside the gates where lines form.

Some cities and stadiums have said they’ll issue heat notifications to the public. Medical personnel will also be stationed and available in FIFA Fan Festivals and around stadiums during matches to manage heat-related illnesses.