EXPLAINER

Paris and other European cities are experiencing temperatures above 40C (104F), reaching levels normally seen across the Middle East.

A blistering heatwave has gripped much of Europe, prompting the highest-level red alerts in parts of the United Kingdom, France, Spain and Italy.

Authorities have warned of health risks, wildfires and travel disruptions as extreme temperatures persist.

With temperatures approaching record highs, officials have taken emergency measures, including a localised alcohol ban in parts of France under red alert, nationwide heat warnings in Germany and the cancellation of a World Cup fan zone screening in Madrid, where temperatures hit 39C (102F).

Why is it so hot in Europe?

A persistent area of high pressure, known as a heat dome, has trapped hot air over Western Europe, bringing clear skies, weak winds and prolonged sunshine. Hot air moving north from North Africa has added to the extreme temperatures.

Unusually warm seas around the UK, Ireland, France and the western Mediterranean have also helped keep coastal areas hot, especially at night. Coastal waters around Spain have reached record warm levels, according to Spain’s port authority.

In the worst-affected areas – western France, England and Wales – daily average temperatures have soared more than 12C above the 1991-2020 baseline, according to Copernicus data.

Scientists say the early-season heatwave is part of a broader warming trend. Europe is the world’s fastest-warming continent, with temperatures rising by approximately 0.56C per decade since the mid-1990s, more than double the global average.

Climate change is making heatwaves more frequent, more intense and likely to occur earlier and later in the year.

How hot are European cities today?

To contextualise the temperatures Europe is dealing with, Al Jazeera looked at the maximum temperatures in five European capitals on June 24 and compared them with cities across the Middle East, North Africa and Asia, where high temperatures are more typically experienced.

Europe is particularly vulnerable – much of its housing and infrastructure was not built for prolonged extreme heat, and only about 20 percent of European homes have air conditioning.

The graphic below shows how European cities’ maximum temperatures today compare with some other cities around the world:

How is temperature measured?

The temperature you see on the news or the weather app on your phone relies on a network of weather stations positioned around the globe.

To ensure accurate readings, weather stations typically use specialist platinum resistance thermometers placed inside shaded instruments known as a Stevenson screen.

Measurements are taken at a standard height of 1.25-2 metres (4-6.5 feet) above the ground. This provides a reading that reflects the air temperature that people actually feel.

There are two well-known scales used to measure temperature: Celsius and Fahrenheit.

Only a few countries, including the United States, use Fahrenheit as their official scale. Most of the world uses the Celsius scale, named after Swedish astronomer Anders Celsius, who invented the 0-100 degree freezing and boiling point scale, although originally inverted, in 1742.

Why does the temperature feel hotter than the forecast says?

Air temperature alone often doesn’t match how hot it feels to your body. That is why forecasts report a “feels like” temperature, which adjusts air temperature based on factors like humidity, wind speed and sun exposure.

Humidity

Humidity measures how much water vapour is in the air. This moisture slows the evaporation of sweat, so your body can’t cool itself as effectively.

Wind speed

In hot weather, a light breeze can help evaporate sweat, making it feel cooler.

Sun exposure

Even if the thermometer reads the same, direct sunlight adds extra warmth, which is why shaded areas feel cooler.