Jul 22, 2022 - Energy & Environment

Heat waves around the world are connected, scientists say

Illustration of a fan blowing on Earth to cool it down.
Illustration: Sarah Grillo/Axios

Two heat waves an ocean apart are inextricably linked.

Why it matters: These kinds of interconnected heat waves could become even more extreme in the future, as human-caused climate change affects the jet stream winds responsible for them.

Driving the news: The jet stream has come under particular scrutiny by climate scientists in recent years due to the hypothesis that the changing temperature difference between the equator and the North Pole could slow down this key weather maker, especially during the summer.

  • Perturbations in the jet stream, or its waviness, can enable the formation and maintenance of intense heat domes such as those that have set up across parts of the U.S. and Europe in the past week.
  • Also linked — multiple heat domes over Asia that have led to heat waves in China, Siberia and Japan.

The big picture: The jet stream travels around the northern hemisphere from west to east, powered by the temperature differences between air masses and more broadly, the difference between the temperature at the Pole versus the equator.

  • It can run straight west to east, in what meteorologists call a "zonal" pattern, or it can be coiled like a snake, known as a highly amplified configuration.
  • Some climate scientists think that over time, climate change is affecting the jet stream in ways that make these contortions, specifically long-lasting, stronger areas of high pressure, or heat domes, more likely to occur.
  • A particular pattern of contortions, known as a wave number 7 pattern, due to the seven peaks and troughs in the upper level winds' path, is associated with the European and U.S. heat waves, and then some, researchers told Axios. Right now, the wave 7 pattern is present, "creating favorable conditions for heat waves around the northern hemisphere," Dim Coumou, a climate researcher at VU Amsterdam, told Axios via email.

Between the lines: A computer system built to detect such human-influenced patterns, run at the Potsdam Institute for Climate Impact Research in Germany, has identified that the European heat wave and U.S. extreme heat were in part related to such a wavy jet stream pattern identified in a 2017 study, said Michael Mann of Penn State University, who was its lead author.

  • That study concluded that the increased occurrence of particular jet stream setups is a possible consequence of increased greenhouse gasses in the atmosphere from burning fossil fuels.
  • Kai Kornhuber, a researcher at Columbia University and co-author of that study, noted that regionally many different factors combine to influence extreme heat events.
  • He, too, said the simultaneous heat waves around the world are consistent with a wave number 7 pattern as identified in the 2017 study.

Threat level: Kornhuber is the author of another paper, published in 2020, that warned of a growing risk that such jet stream setups will lead to simultaneous heat waves and dry conditions over multiple breadbasket regions.

  • The pattern laid out in that paper is eerily similar to the heat waves of the past week, which have hit the Plains, grain-producing areas of central North America, and western and eastern Europe, he told Axios in an interview.

What they’re saying: "What we're seeing right now is a slowdown of midlatitude circulation in summer," said Kornhuber. This influences heat waves since it makes them last longer. "The longer they last the more intense they get," he said.

  • In addition to the jet stream's effects, heat waves are becoming more intense due to the warming climate itself and feedbacks with drier soils that can cause temperatures to climb further, he said.
  • "It's not clear if this particular wave seven pattern is going to occur more frequently, but what I can say with all clarity is that each of those hotspots that we identify there, Europe, North America, Central Asia, these heat waves that are associated with this wave seven pattern, they will just increase the magnitude," he said.
  • "The risk of concurrent breadbasket failures is increasing."

Editor's note: This story has been corrected to fix the spelling of Dim Coumou's name and to note that he is a climate researcher at VU Amsterdam not the University of Amsterdam.

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