Countries in Western and Central Europe - including Spain, France and the United Kingdom - have issued red alerts because a heat wave is expected to intensify in the coming days with temperatures that will exceed 40 °C.

More than half of France's regions are currently under the maximum weather alert level and hundreds of schools have been ordered to close.

The French country recorded the hottest day since records exist (44.3ºC in Pissos, Landes), while the drowning death of at least 40 people has been confirmed while swimming in unsupervised areas in recent days.

“It is not something that should be taken lightly: swimming in unsupervised areas during a heat wave,” French Minister of Sports and Youth Marina Ferrari told French radio.

Ferrari said too many people were trying to cool off in rivers and canals without necessarily considering the risks.

Among the fatalities was a 13-year-old girl who had gone to bathe with her family in the River Seine, near Fontaine-le-Port, on Sunday afternoon, even though she did not know how to swim.

Several people also drowned in Germany, while temperatures are expected to reach up to 40°C in the west and south-west of the country by the end of the week.

In Spain, the Spanish State Meteorological Agency (Aemet) warned this week of “extremely high” temperatures for the time – between five and ten degrees above usual –, with some areas that could reach 44 °C.

A red alert has been issued for the Basque Country, where highs in San Sebastián are expected to reach 40°C, almost double the average for this time of year.

The UK Met Office has issued a rare red heat alert for parts of England and Wales on Wednesday and Thursday, with temperatures forecast to reach 38°C in some areas.

Authorities in Italy, Switzerland and Luxembourg have issued similar red warnings.

The immediate cause of this increase in temperatures is a “heat dome”: a mass of warm air moving north from the Sahara is “stuck” over Europe, trapping hot air inside.

This mass is fed by a powerful high pressure system known as the “African anticyclone.”

More intense and lasting heat

Scientists stress, however, that there is no doubt that the recurrence of heat waves is an indicator of human-caused climate change, largely the result of the burning of coal, oil and gas.

Météo-France highlights that, of the 51 heat waves recorded in France since 1947, 34 have occurred since 2000 and 26 since 2011.

The UK Met Office estimates that the extreme heat seen during recent heatwaves is ten times more likely now due to climate change, and these events are not only more intense, but also last longer.

In the last 50 years the length of warm periods has doubled.

“Human-caused climate change has served as a launching pad for this phenomenon, loading the atmosphere with additional heat and making extreme temperatures much more intense than they would have been in the past,” explains Dr. Akshay Deoras, a researcher at the National Center for Atmospheric Sciences at the University of Reading, England.

But the determining factor of this phenomenon, adds the researcher, is a “heat dome.”

What is a heat dome

“Imagine it as a huge atmospheric cap that prevents cloud formation and allows a relentless sun to heat the ground day after day,” explains Dr. Deoras.

“At the same time, the air descending under the high-pressure system is compressed and heated, much like the air inside a bicycle pump is heated when operated.”

It is essentially a mass of hot air stubbornly rooted in one place, trapping those inside at ground level in a prolonged heat wave.

Scientists believe these events are caused by a sharp change in ocean temperatures.

In turn, rising water temperatures warm the air, and winds push that heat toward the land.

Once the warm air reaches land, it is trapped by a high-pressure system, forming a dome flanked by low-pressure systems on both sides.

The high pressure further heats the air column by compressing it, effectively acting as a dome.

Climate change: what's to come

These record-breaking heat waves have occurred in a world that is, on average, about 1.4°C warmer than it was at the end of the 19th century, due to human activities such as the burning of fossil fuels.

However, global warming could approach 3°C by the end of the century, depending on the current climate policies of governments around the world.

This will inevitably mean new temperature records, posing particular challenges for countries such as the United Kingdom and Switzerland, whose infrastructure and buildings are not prepared for extreme heat.

“The climate we live in today is simply not the one we grew up with; our buildings and infrastructure are woefully ill-prepared for what is to come,” warns Friederike Otto, professor of climate sciences at Imperial College London.

Until 1990, the UK temperature record for any month was 36.7°C, set in 1911.

Since then, that figure has been exceeded several times and currently stands at 40.3 °C, a mark registered in July 2022.

As climate change progresses, even higher temperatures will soon be a real possibility, warns Richard Betts, head of climate impacts research at the Met Office and professor at the University of Exeter.

“Until we reduce global carbon emissions to net zero, we will continue to warm the planet and temperature records will continue to be broken,” he said.