Portugal, whose bucolic landscape reveals rolling hills speckled with olive trees and centuries-old stone villages, became a landscape of fear this summer. When a heat wave began to steamroll the country in early July, residents were forced indoors to take what refuge they could behind drawn shutters while outside the heat continued to bake forests and crops already parched from a prolonged drought.

Aided by swift winds and dry conditions, the intense heat sparked dozens of wildfires across the country and in neighboring Spain. Portuguese farmers fled the flames carrying sheep on their backs. Near the Quinta do Lago golf resort in the south, drivers had to turn back as flames and smoke eddied across highways. Even in areas not directly touched by the flames, such as the coastal city of Aveiro, residents struggled to breathe as smoke from fires raging a few miles to the east enveloped some neighborhoods. Thousands were evacuated from their homes across the country.

As blazes burned across Portugal, the searing heat smashed records. In Pinhão, a picturesque village perched on the banks of the Douro River in North Central Portugal, temperatures hit 47.2 degrees Celsius, according to reports from the Portuguese Institute of the Sea and Atmosphere.

Suspected heat-related deaths began to mount. Spanish health authorities have reported a total of 3,952 excess deaths related to the summer’s heat waves. Similar figures haven’t been released for Portugal yet, but at the height of its first heat wave, between July 7 and July 18, the Portuguese health ministry reported that there were 1,063 more deaths than would have been expected for this period.

Even as crews managed to contain some of Portugal’s worst wildfires, the heat continued to cook the northeast of the country, as well as much of Spain and parts of France, Greece, and Turkey. The extreme weather then expanded northward to the UK, where the Meteorological Office issued its first-ever red warning for exceptional heat in the typically cool, wet country, urging residents to brace for temperatures as high as 40 degrees Celsius—a record-breaking first for England that arrived a few days later.

“Temperatures hopping up into the mid-40s does not happen too often, even in Spain or in Portugal,” says Paul Hutcheon of the UK Met Office. Luton airport, which serves London, had to temporarily suspend flights after part of its runway buckled in the heat, while fires broke out across the country.

“The infrastructure is just not built for temperatures of up to 40 degrees Celsius,” says Friederike Otto, a climatologist at Imperial College London’s Grantham Institute for Climate Change and the Environment. “Buildings, schools, and hospitals are neither air conditioned or insulated. Houses don’t have shutters or anything to keep out the heat. People are not aware of the dangers of the heat, and they don’t know how to deal with it.”

While heat waves have occurred in Europe on occasion, they’re becoming far more frequent and intense, and are sticking around for longer. And climate change is largely to blame. When a heat wave swept across Europe in 2019, Otto—who coleads World Weather Attribution, a research collaborative that analyzes climate change’s contribution to extreme weather events—immediately conducted an assessment with her team to see if they could detect global warming’s fingerprints. They did: Climate change made the high temperatures five times more likely, they found.

Other studies over the past few years have come to similar conclusions. The first to look at climate change’s effects on a heat wave in Europe, conducted after the devastating 2003 event that killed more than 70,000 people, found that global warming had made the heat wave twice as likely to happen. Other analyses have found that severe heat waves, like the one that swept the northwestern United States last year or the Siberian heat wave in 2020, would have been impossible without climate change.

“We do not need to do another attribution study” to know that climate change has played a role in this year’s heat waves and fires, says Otto. “So many attribution studies about different heat waves have been done in recent years, all finding the same thing—that climate change has been a game-changer in all of these.” Given that these heat waves are clearly caused by climate change, and that the world will continue to warm, the worst is almost definitely yet to come.

With land temperatures in Europe projected to increase by at least another 1.2 to 3.4 degrees Celsius by the last few decades of this century, heat waves and wildfires like the ones that have broiled Europe this year will eventually become commonplace and affect more land area. Drought, too, will become more frequent. Temperatures during future heat waves could hit 50 degrees Celsius or higher, particularly in the Mediterranean, where the influence of hot air from Africa is strongest, the UK Met Office’s Peter Stott warned last year. (Punishing heat baked Europe this summer because of a low-pressure spot, initially parked off Portugal’s west coast, that pulled hot air up from northern Africa. As it shifted northward, it brought the extreme heat with it.)

But as temperatures continue to rise, not all of Europe will suffer equally. “The burden of climate change shows a clear north-south divide, with southern regions in Europe much more impacted, through the effects of extreme heat, water scarcity, drought, forest fires, and agriculture losses,” warned a 2020 report by the European Commission’s Joint Research Center. The double hit of drought and heat waves will cause up to a 50 percent drop in crop yields in Southern Europe by 2050 and might even force farmers to abandon agriculture altogether, even as yields in parts of Northern Europe increase, according to a 2019 report by the European Environment Agency.

But while recent research has shown that European heat waves—defined in this region as heat above normal thresholds lasting at least six days—have become more frequent and more intense over the past four decades, and are doing so at a faster rate than other regions at the mid-latitudes, scientists are still unpicking exactly why this is happening.

Heat waves are caused by several complex and often interacting factors, including changes to currents high in the atmosphere and in the ocean, soil moisture, and overall temperature trends. But a study published this summer shed new light on one of these factors: atmospheric currents. Recent heat waves in Europe have coincided with periods when the jet stream that moves across the Atlantic split in two, resulting in weaker winds that allow heat waves to form, the study found.

“We found those double jet-stream states have almost doubled in frequency,” says lead author Efi Rousi, who was a senior scientist with the Potsdam Institute in Germany at the time of the study (she is now editor of the journal Nature Communications, where the study was published). “Before, a double jet used to last a few days—now it lasts up to one month.” A jet stream split coincided with Europe’s July heat wave and may have contributed to the low pressure that helped scorch Europe. Members of the study team are working on figuring out what’s causing these changes to the jet stream.

For now, with even more extreme heat coming in the not-too-distant future, Europe—and much of the rest of the world—needs to prepare in order to reduce the risks to people, crops, and ecosystems, says Alex Robinson, a climate scientist with the Complutense University of Madrid.

“There’s no upper limit” on just how bad things can get, he says. “As long as global warming keeps going, the heat waves will get more and more extreme. We’re moving into a territory now that we’re really starting to see unprecedented heat waves, and it’s something that society isn’t adapted to.”

Updated 9-22-2022 11:30 am ET: Spain’s excess death figure was updated to the latest total.