July’s extreme heat waves ‘virtually impossible’ without climate change

A recent report found that global warming is not only increasing the amount heat waves, but making them hotter.
A billboard displays a temperature of 118 degrees Fahrenheit during a record heat wave in Phoenix, Arizona on July 18, 2023. Swaths of the United States home to more than 80 million people were under heat warnings or advisories, as relentless, record-breaking temperatures continued to bake western and southern states.

A billboard displays a temperature of 118 degrees Fahrenheit during a record heat wave in Phoenix, Arizona on July 18, 2023. Swaths of the United States home to more than 80 million people were under heat warnings or advisories, as relentless, record-breaking temperatures continued to bake western and southern states. Patrick T. Fallon/AFP via Getty Images

Extreme heat waves roaring across North America, Europe, and China this month were exacerbated by climate change, according to an early analysis released July 25 by the World Weather Attribution (WWA) initiative. The group,  an international group of volunteer scientists who assess climate change’s role in extreme weather, says that the heat baking parts of the United States and southern Europe would not have occurred without climate change. Additionally, they write that climate change made China’s historic heat wave at least 50 times more likely.

[Related: How ‘underground climate change’ affects life on the Earth’s surface.]

“Had there been no climate change, such an event would almost never have occurred,” study lead author Mariam Zachariah, a climate scientist at Imperial College of London, told the AP.  Zachariah called heat waves in Europe and North America “virtually impossible” without climate-change induced temperature rises. 

Since July began, dangerous heat waves have killed livestock and crops, triggered wildfires, stressed hospitals, and are responsible for multiple deaths across three continents. More than 100 people have died from the heat in Mexico since March, while Death Valley, California hit 128 degrees Fahrenheit  this month. China posted an all-time national temperature record of 126 degrees Fahrenheit earlier this month, while parts of Italy and Spain are moving towards Europe’s all time record of 119.8 degrees. The city of Phoenix, Arizona is expected to experience its 26th consecutive day with temperatures above 110 degrees today, smashing a record of 18 days set in 1974

In this new analysis, the WWA team examined weather data and computer model simulations to compare the Earth’s current climate, which has warmed about 2.2 degrees Fahrenheit since the late 1800s, with the climate of the past.  The study found that not only has climate change increased the likelihood of these heat waves happening, but it is making them hotter. Earth’s stagnant atmosphere, warmed by carbon dioxide and other gasses, made Europe’s heatwave 4.5 degrees hotter, China’s 1.8 degrees warmer, and the southern US and Mexico’s heatwave 3.6 degrees hotter. 

Extreme heat waves like these are expected once every 15 years for the US and Mexico, once every 10 years in Southern Europe, and once every five years for China, according to the analysis.  “They are not rare in today’s climate,” WWA co-leader and Imperial College London climate scientist Friederike Otto told The Washington Post. “What surprises me is that people are so surprised. It is exactly what we expected to see.” 

[Related: A cap on ‘luxury’ emissions could make a clean energy transition fairer.]

Otto added that the findings support a growing scientific consensus that the warmer the world gets, crippling heat waves, stronger storms, and climate-fueled disasters will be only more likely. 

While dire, this study should not be interpreted as evidence of “climate collapse” or as a situation we are powerless to stop, according to the team. The report stressed that we still have time to do something about climate change, but society must quickly reduce emissions of planet-heating pollution. They also encouraged countries and cities around the world to adapt sustainable energy systems, urban planning, and public health initiatives to better prepare for the extreme heat to come. 

“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 told CNN. “If we do not, tens of thousands of people will keep dying from heat-related causes each year.”