Dec 17, 2021 - Energy & Environment

Study: Risk of overlapping heat waves grows in Northern Hemisphere

Picture of a woman cooling herself off at a water fountain in California during a heat wave.
A resident splashes water onto their face during a heat wave in Sacramento, Calif., July 8, 2021. Photo: David Paul Morris/Bloomberg via Getty Images

The risk of large heat waves happening simultaneously in at least two parts of the Northern Hemisphere is growing due to global warming and its effects on atmospheric circulation, a new study finds.

Why it matters: The study, accepted for publication in the Journal of Climate, adds to concerns about food supply disruptions and other major societal impacts, depending on the location of the concurrent extremes.

Driving the news: The research, led by Cassandra Rogers, a post-doctoral researcher at Washington State University, examined climate data from 1979 to 2019 and found a six-fold increase in the number of simultaneous large heat waves occurring in the Northern Hemisphere warm season between the 1980s and 2010s.

  • During the same period, the heat events grew in size and intensified. The study was discussed Thursday at a major Earth science meeting in New Orleans.

Details: While heat waves themselves can pose huge risks to human health, with hundreds of deaths attributed to last summer’s Pacific Northwest heat wave, for example, they can also prime the environment for wildfires and affect agriculture.

  • A 2019 study by Columbia University’s Kai Kornhuber, a co-author of the new research, found that simultaneous heat waves caused about a 4% decrease in crop production.
  • That research identified specific patterns of the jet stream, which steers storms, that are associated with heat extremes that tend to occur simultaneously in different breadbasket regions.
  • One such pattern, for example, can cause heat waves to break out in central North America, Eastern Europe and East Asia, the study found.

What they did: This study quantified large heat waves as periods of three or more days with daily mean temperature greater than the local 90th percentile with a range roughly the size of Mongolia or Iran (about 620,000 square miles).

  • The researchers were able to show that the primary driver of the increase in simultaneous heat waves is the background warming of the climate, plus warming's influences on atmospheric circulation, through changes in the jet stream, for example.

What they’re saying: "The fact that we know what's happening, we know these events are going to continue to happen, is a real opportunity to actually prevent the deaths that could happen," Rogers told Axios.

  • "I think it's a little silver lining there, as bad as the predictions are,” she added
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