Phoenix, Ariz., has had 25 consecutive days of temperatures above 110 degrees Fahrenheit (43.3 degrees Celsius) amid the unrelenting heat dome that has been clamped firmly in place over the U.S. Southwest and Mexico. Meanwhile the township of Sanbao in the Xinjiang Uygur region of China, has set the country’s all-time record high temperature of 126 degrees F (52.2 degrees C) as parts of China have baked in a heat wave. And yet another record-breaking heat event has been roasting southern Europe, giving Spain’s region of Catalonia its hottest-ever temperature of 113.7 degrees F (45.4 degrees C).
Such events are quickly becoming more and more routine. And without the excess heat trapped by the gases released from burning fossil fuels, such extreme heat would rarely—if ever—happen, according to a new study published on Tuesday by an international group of researchers called World Weather Attribution (WWA). The results echo the group’s previous work, which found that climate change has made various extreme heat events (including a heat wave in South Asia in April, one in the western Mediterranean that month and an early-season heat event in Paraguay and Argentina last year) many times more likely to occur. Those consistent findings underscore how crucial it is that the world cease burning fossil fuels as quickly as possible—and adapt to handle the increasingly intense and frequent heat waves that are a hallmark of the climate emergency.
“The role of climate change is absolutely overwhelming,” said study co-author Friederike Otto, a climate scientist at the Grantham Institute–Climate Change and the Environment at Imperial College London, at a press conference on Monday.
WWA researchers used peer-reviewed methods to look for the fingerprints of climate change in extreme weather events. They examined temperature trends over time and employed computer models to compare today’s climate with a theoretical world without human-caused climate change.
For the new analysis, the WWA team found that the heat wave in China was 50 times more likely to have occurred in a warming world and that those in Europe and southern North America would have been “virtually impossible” without climate change. In today's climate, events of such magnitude would be expected to happen about every 15 years in North American, every 10 years in Europe and every five years in China. “The heat waves we are seeing now, we definitely have to live with that,” Otto said at the press conference.
Not only are these heat waves coming more often, but they are also considerably hotter. The one in Europe had temperatures that were 4.6 degrees F (2.5 degrees Celsius) higher than they would have been without climate change. The North American event was 3.6 degrees F (two degrees C) hotter, and China’s was 1.8 degrees F (one degree C) warmer.
The planet as a whole has warmed by about 2.2 degrees F (1.2 degrees C) since preindustrial times. Under the Paris climate accord, countries have agreed to limit global warming to “well under” 3.6 degrees F (two degrees C) above preindustrial levels and to striving to limit such warming to 2.7 degrees F (1.5 degrees C). If the global average temperature rises from its preindustrial state by two degrees C—which will happen within 30 years, barring rapid declines in greenhouse gas emissions—such heat waves will happen about every two to five years, the WWA team says.
A 2022 study that looked at how climate change was influencing simultaneous heat waves in different parts of the world found that they are happening seven times as often as in the 1980s and that they are stronger and cover larger areas today.
The specter of hotter and more frequent heat waves raises enormous concerns about public health. Heat is the deadliest of all weather-related extremes in the U.S., killing more people than hurricanes, tornadoes and flooding combined. It is especially a risk for young children, the elderly, those with health conditions such as asthma and heart disease, those who work outside and unhoused people. Where people do have access to air-conditioning, that lifeline can be threatened by the extra demand placed on the power grid when temperatures rise—potentially leading to blackouts that expose even more people to dangerous heat.
Heat-related deaths have been reported in all affected areas—including more than 200 in Mexico alone. But any current mortality tolls are almost certainly an undercount because it takes time to ascertain and record causes of death. Last year heat waves in Europe killed an estimated 60,000 people, a recent study found.
Such extremes also pose major economic concerns. The recent heat waves have led to major decreases in crop yields, including olives in Spain and cotton in China, as well as the deaths of cattle in Mexico. There are also concerns that more intense summer heat will keep tourists away from places such as Spain and Italy.
The impacts show that “we need a cultural shift in the way we think about extreme heat,” said Julie Arrighi, a review author of the new study and interim director of the Red Cross Red Crescent Climate Center, in a WWA press release about the findings. “It is crucial to scale warning systems, heat action plans and investments in long-term adaptation measures. This includes urban planning and bolstering resilience of critical systems such as health, electricity, water and transport.”
The study authors have also emphasized the message that humanity still can—and must—act to rein in climate change.
“These heatwaves are not evidence of ‘runaway warming’ or ‘climate collapse.’ We still have time to secure a safe and healthy future, but we urgently need to stop burning fossil fuels and invest in decreasing vulnerability,” Otto said in the recent WWA press release. “If we do not, tens of thousands of people will keep dying from heat-related causes each year.”