Study sees traces of climate change in July heat waves in Europe, China and America

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The traces of climate change are present in the intense heat waves that hit the planet this month, according to a new study. The researchers argue that the deadly heat waves in the southwestern United States and southern Europe could not have occurred without the continued buildup of greenhouse gases in the atmosphere.

These unusually powerful heat waves are becoming more frequent, the study indicated Tuesday. The same research found that the increase in greenhouse gases, coming mostly from the burning of coal, oil and natural gas, has made another heat wave, the one that hit China, 50 times more likely and can occur every five years or so.

A stagnant atmosphere, heated by carbon dioxide and other gases, also caused the heat wave in Europe to be 2.5 degrees Celsius (4.5 degrees Fahrenheit) higher, worsened the United States and Mexico by 2 degrees C (3.6 F) and China by 1 degree C (1.8 F), according to the study.

Using tree rings and other temperature records, several climatologists have pointed out that this month’s heat is probably the most intense the Earth has experienced in some 120,000 years, and easily the highest in human civilization.

“If there had been no climate change, such an event would almost never have occurred,” said study lead author Mariam Zachariah, a climatologist at Imperial College London. Heat waves in Europe and North America would be “virtually impossible” without rising temperatures since the mid-19th century, she added. Statistically, China’s could have occurred without global warming.

Since the advent of industrial-scale combustion, the planet has warmed by 1.2 degrees Celsius (2.2 F) so “not unusual in today’s climate and the role of climate change is absolutely daunting,” said Imperial College climatologist Friederike Otto, who leads the World Weather Attribution team of volunteer international climate scientists conducting these studies.

In this climate scenario, especially intense heat waves that scorch Texas, California, Arizona, New Mexico, Nevada, Baja California, Sonora, Chihuahua, and Coahuila are now likely to occur once every 15 years.

But the climate is not stabilized, not even at this level. If it rises a few tenths of a degree more, the heat this month will be even more common, Otto said. Phoenix has broken the record for 25 consecutive days with temperatures at or above 110 Fahrenheit (43.3 degrees Celsius) and more than a week with nighttime temperatures never dipping below 90 F (32.2 C).

It is possible that with the current climate, the heat that is registered in Spain, Italy, Greece and in some countries of the Balkans is repeated every decade.

Since the researchers began analyzing the three simultaneous heat waves on July 17, the results have not yet been reviewed by other experts, as is usual in scientific studies. But they used scientifically valid techniques, their research is regularly published, and some independent experts told The Associated Press that their conclusions make sense.

The way the scientists do these quick analyzes is by comparing observations of the current climate in the three regions with repeated computer simulations of “the world that could have been without climate change,” said Izidine Pinto, a climatologist at the Royal Netherlands Meteorological Institute and a co-author of the study.

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Borenstein is on Twitter at @borenbears

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The Associated Press’s climate and environmental coverage is supported by several private foundations. The AP is solely responsible for the content.