Heatwaves have been steadily getting intense, longer and more frequent across the globe, with the latest one scorching much of Europe after a record-shattering one burned through India and Pakistan back in March.
These are unmistakable signs of climate change, experts say.
Humans to blame
"Every heatwave that we are experiencing today has been made hotter and more frequent because of human-induced climate change," said Friederike Otto, senior lecturer at Imperial College London's Grantham Institute for Climate Change.
"It's pure physics, we know how greenhouse gas molecules behave, we know there are more in the atmosphere, the atmosphere is getting warmer and that means we are expecting to see more frequent heatwaves and hotter heatwaves."
In recent years, advances in the discipline known as attribution science have allowed climatologists to calculate how much global heating contributes to individual extreme weather events.
The India-Pakistan heatwave, for example, was calculated to have been 30 times more likely with the more than 1.1 degrees Celsius (1.8 degrees Fahrenheit) of warming that human activity has caused since the mid-19th century.
The heatwave that shattered records in North America in June 2021, leaving hundreds dead as temperatures soared to 50 degrees Celsius in places, would have been virtually impossible without global heating.
And the last major European heatwave, in 2019, was made 3 degrees Celsius hotter by climate change.
"The increase in the frequency, duration, and intensity of these events over recent decades is clearly linked to the observed warming of the planet and can be attributed to human activity," the World Meteorological Organization said in a Monday statement.
Worse to come
However unbearable temperatures get this week, scientists are unanimous: there is worse to come.
At 1.5 degrees Celsius of warming – the most ambitious Paris climate agreement goal – United Nations climate scientists calculate that heatwaves will be more than four times more likely than the pre-industrial baseline.
At 2 degrees Celsius or warming, that figure reaches 5.6 times more likely, and at 4 degrees Celsius heatwaves will be nearly 10 times more likely to occur.
Although three decades of U.N.-led negotiations, countries' climate plans currently put Earth on course to warm a "catastrophic" 2.7 degrees Celsius, according to the U.N.
Matthieu Sorel, a climatologist at Meteo-France, said that climate change was already influencing the frequency and severity of heatwaves.
"We're on the way to hotter and hotter summers, where 35C becomes the norm and 40C will be reached regularly," he said.
Danger of death
The heatwaves of the future depend largely on how rapidly the global economy can decarbonize.
The U.N.'s climate science panel has calculated that 14% of humanity will be hit with dangerous heat every five years on average with 1.5 degrees Celsius of warming, compared with 37% at 2 degrees Celsius.
"In all of places in the world where we have data there is an increase in mortality risk when we are exposed to high temperatures," said Eunice Lo, a climate scientist at the University of Bristol's Cabot Institute for the Environment.
It's not only the most vulnerable people who are at risk of health impacts from heat, it's even the fit and healthy people who will be at risk."
There is a real risk in the future of so-called "wet bulb" temperatures – where heat combines with humidity to create conditions where the human body cannot cool itself via perspiration – breaching lethal levels in many parts of the world.
As well as the imminent threat to human health, heatwaves compound drought and make larger areas vulnerable to wildfires, such as those now raging across parts of France, Portugal, Spain, Greece and Morocco.
They also menace the food supply.
India, the world's second-largest wheat producer, chose to ban grain exports after the heatwave impacted harvests, worsening a shortage in some countries prompted by Russia's invasion of key exporter Ukraine.