The results came with a sobering reminder: Once inexplicable heat waves not only occur, but become more common.
“They are not unique to today’s climate,” Friederike Otto, co-leader of the group and a climate scientist at Imperial College London, said in an interview. “What surprised me was that people were so surprised. This is exactly what we were looking forward to seeing. “
Not that there’s anything ordinary about the triple-digit temperatures that have gripped many parts of the planet this summer, shattering temperature records, threatening plants and wildlife and endangering the health of tens of millions of people every day.
At least scientifically, Otto said, the findings support a growing consensus among researchers: The warmer the world gets, the more likely regions will experience heat waves, stronger hurricanes and other climate-fueled disasters.
Otto and researchers from the United States, the United Kingdom and the Netherlands sought to quantify the impact of climate change on the heat waves that occurred earlier this month in three regions: the US Southwest and parts of Mexico, southern Europe and a swath of China.
Using data and simulations that compare the current climate with the past, they examined the times in July when the heat was most intense in each region — 18 days in the western United States and parts of Mexico, one week in southern Europe and 14 days in the lowlands of China.
Finally, they know that the heat waves that are baking in Southwest and southern Europe have almost no chance of happening in a world without climate change. A Chinese heat wave is made about 50 times more likely given global warming, the study found, while European and North American heat waves are at least 1,000 times more likely.
The findings have not yet been peer-reviewed, due to the rapid timeline in which the study was completed, but the team used a set of peer-reviewed methods to detail each area’s climate change fingerprint.
In recent years, the team has used such methods to identify dozens of heat waves, extreme rains, hurricanes, droughts and floods that are becoming more likely or worse with climate change. Others, such as the 2021 Pacific Northwest heat wave that killed hundreds of people, were also found to be “virtually impossible” in a world unchanged by greenhouse gas emissions.
As rare as this month’s heat waves were not long ago, they are becoming less rare.
Heat waves like those in Tuesday’s study have about a 1-in-15 chance of occurring any year in North America, about a 10 percent chance of occurring any year in southern Europe and approximately a 20 percent chance of occurring any year in China, the authors said.
In each case, the team found, human-caused greenhouse gas emissions made the heat wave hotter than it would have been otherwise: an estimated 2.5 Celsius (4.5 Fahrenheit) warmer for the European heat wave, 2 Celsius (3.6 Fahrenheit) warmer in North America and 1 Celsius (1.8 Fahrenheit) warmer in China.
The researchers behind Tuesday’s study said they did not specifically examine the role of the El Niño climate pattern that developed this summer and is known to raise temperatures and change weather patterns. But they say climate models account for such differences, and that whatever role El Niño plays in land-based heat waves pales in comparison to a warming atmosphere.
“Although El Niño is feeding the numbers, the signal remains the same,” said Mariam Zachariah, a researcher at Imperial College London and a co-author of the study. “The climate change signal is still clear.”
Despite emerging evidence, he said, what July showed “is how vulnerable our societies are to these changes.”
Already, the group said, the United States has logged many heat-related deaths, including among migrants trying to cross the border from Mexico. More deaths were reported across Spain, Italy and other European countries, as well as in China. Hospitalizations spiked as heat-stroke patients sought emergency care, outdoor workers succumbed to scorching temperatures and the unrelenting heat caused an increase in demand for electricity.
“It emphasizes the need for our systems to adapt faster, because the risks are faster than our adaptation,” Julie Arrighi, director of the Red Cross Red Crescent Climate Center, which works to reduce the effects of extreme weather events on vulnerable people, told reporters in a call on Monday.
Arrighi said leaders from the local to the national level need to embrace “a cultural change” in the way they think about extreme heat and its hazards. As heat waves worsen and become more common, it is important to increase warning systems, develop plans to provide people with cool places to escape and strengthen the stability of electric grids, water supplies and health systems.
In recent years, scientists say with increasing confidence that not only are humans increasing the number of extreme weather events around the planet, but that the frequency and severity of such disasters are likely to worsen over time.
The Intergovernmental Panel on Climate Change (IPCC), a United Nations-backed collection of some of the world’s top climate scientists, wrote in its latest report that “it is almost certain that heat extremes (including heat waves) have become more frequent and more severe in most regions of the earth since the 1950s.”
Meanwhile, the panel wrote, instances of extreme cold “have become less frequent and less severe.”
In its first report, the IPCC stressed that episodes of extreme heat “will continue to increase” worldwide. Even if humans manage to limit the Earth’s warming to no more than 1.5 Celsius – the most ambitious goal set out in the 2015 Paris climate accord – extreme heat events will increase in the near term, scientists say.
If the world can’t stop warming the planet, the problem will only get worse over time. “Compared to current conditions, changes in the intensity of extremes will be at least double 2 (degrees Celsius), and quadruple 3 (degrees Celsius) of global warming, compared to changes of 1.5 (degrees Celsius),” wrote the IPCC.
Even without Tuesday’s study, the scorching weather that has engulfed parts of the planet in recent weeks offers the latest round of evidence of just how much things have changed.
Scientists say July is likely to end up as the hottest month on Earth on record, and possibly in more than 100,000 years. Day by day, records of average annual temperature around the world are falling.
For most of the month, Phoenix endured daily highs above 11o. The temperature in a Chinese town reached 126 degrees Fahrenheit. In the Middle East, the heat index reached 152 degrees Fahrenheit, pushing the levels believed to be the worst the human body can withstand.
As with previous heat waves, such as the brutal stretch that claimed more than 60,000 lives across Europe last summer, the lingering question is whether policymakers around the world can act quickly — or muster the resources — to help those most at risk avoid the deadliest form of extreme weather.
“The good news about heat is that we know a lot of different adaptations that help,” said Jane Baldwin, an assistant professor of Earth system science at the University of California at Irvine, who was not involved in Tuesday’s study. “The bad news is that there are still many areas where we haven’t taken full advantage of it.”
Otto assured that the surprising heat waves of recent weeks, although not unusual in a warming planet, do not represent a new reality.
“We don’t know what the new normal is until we stop burning fossil fuels. We’re not in a stable climate,” he said.
Until the trajectory of human emissions falls sharply, temperature records will continue to fall. The heat waves grow fiercer and more numerous, providing only a glimpse of potentially hotter parts ahead.
“It doesn’t look like much of the future,” Otto said. “It’s going to be a cold year next summer. This is not what we have to get used to. We have to get used to it, and worse.”