Longer, hotter heatwaves leading to rise in heat stress around the world

Heatwaves around the world are getting hotter and lasting longer according to a new study. Scientists analysed a global dataset of human heat stress using a measurement called the Universal Thermal Climate Index and found some subtropical countries are experiencing 50 more days per year of at least strong heat stress compared with the 1970s.

Searing daytime temperatures of 45 Celsius (113 Fahrenheit) are ensuring many people here in the Iraqi capital Baghdad wait until night time before they venture outdoors.

They are not alone.

According to a new study published in the journal Nature Climate Change extreme 'feels-like' temperatures, heat stress days and tropical nights have all become dramatically more frequent.

The study was carried out by researchers from the European Centre for Medium-Range Weather Forecasts.

They say heatwaves have become longer and more severe over the past six decades as the planet's warming intensifies, the result of the burning of fossil fuels coal, oil and gas.

They assessed heat stress on individual humans, influenced by temperature, humidity, wind speed and more, using what’s called the Universal Thermal Climate Index to analyse those factors and model the human body’s response to the environment.

The combination of heat and humidity can be dangerous for humans, because humidity impacts how sweat evaporates, and that's a cooling mechanism.

Taxi driver Aziz Latif says he works at night and it seems he makes more money at night because no-one wants to make journeys during the day.

“The night (shift) is much better for me, as I said first the weather cools down in the night and more people are coming out, and it is better for the car and myself as I can be relaxed in the cool weather. While during the day, there are not many people outside and the weather is hot. The car and I get tired and might not even make a single journey,” says Latif.

Dangerous heat

Heat waves that are humid can be more fatal than dry heat waves as humans don't cool down as easily.

Heat stress is worsening in already-warm regions, and beyond.

Past studies have looked at the extent to which human-driven climate change has sent temperatures soaring, especially in recent years. One study says people globally suffered an average of 41 extra days of dangerous heat in 2024.

Some research says that the world is on track to add nearly two months of superhot days each year by the end of the century.

Here, researchers looked at heat stress at three levels: strong (index temperatures of greater than or equal to 32 degrees Celsius, or 89.6 degrees Fahrenheit); very strong (index temperatures of greater than or equal to 38 degrees Celsius, or 100.4 degrees Fahrenheit); and extreme (index temperatures of greater than or equal to 46 degrees Celsius, or 114.8 degrees Fahrenheit).

Places that might see around 50 more days per year of at least strong heat stress compared with the 1970s include parts of Southern Africa, such as in Namibia and Angola; Eastern Africa, including parts of Tanzania, Kenya and Uganda; and parts of Mexico and Central America.

Extreme heatwaves are increasing in other countries too, although they may not be as prolonged.

Adapting

These streets are busier now at night than they are during the day.

Iraqis are are trying to adapt.

With climate change, poor infrastructure and state planning, and a lack of green spaces, the challenge of staying cool is becoming harder each year.

The scorching peak summer heat has reached 45 C (113°F) in the Iraqi capital, and as a result, shops have taken it upon themselves to provide some much-needed relief.

Soaring temperatures have compelled Iraqis to get creative as they attempt to stay cool amid frequent power outages.

In Baghdad's busy market streets, they've set up makeshift cooling systems by attaching water sprinklers to electric fans.

But that doesn’t work in bakery shops and other indoor businesses

“It doesn’t make a big difference as we are working beside the burning fire, which doesn’t make a huge difference whether it was day or night,” says Mohammed Hussein, a baker.

According to Hussein the area next to the oven can reach as much as 70 degrees.

One billion more people face at least one day of extreme heat stress each year compared with the 1970s, according to a Nature Climate Change paper.

Not only that but the nights are getting hotter The findings show that global heat stress is intensifying across events during the day, night, and during both the day and night.

The study's lead author Rebecca Emerton from the European Centre for Medium Range Weather Forecasts says we can now compare how much hotter the climate now than it was for our grandparents generation:

"So what we've really done is we've kind of focused on mapping the difference in heat stress between particularly the 1970s and our current climate, so a recent ten years to help people understand how hazardous heat has already changed in our lifetimes, or the lifetimes of our parents or our grandparents," she says.

She explains the weather trajectory we're on means the heat will intensify.

"As our, atmosphere warms overall, it gets better at trapping heat and other changes such as atmospheric circulation, solar radiation, cloud cover it varies across the globe, the exact, amount of each factor, but these all add up to us seeing more frequent, more intense, longer lasting heat waves and, chronic heat around the globe," says Emerton.

Chemists are already noting the impact of the heat on health especially for people with asthma and allergy issues.

“We receive serious cases including fainting, asthma, and sinus. We receive a lot of cases daily and there many medicines prescribed due to allergy issues and hot temperatures,” says Dr Abu al Fadhil Hasanein, a pharmacist in Baghdad.

Recent official data has shown at least five Iraqi cities ranking among the world's hottest cities every day.

One billion more people face at least one day of extreme heat stress each year compared with the 1970s, according to a Nature Climate Change paper.