Since 1979 climate change made heat waves last longer, spike hotter: study

A new study finds that climate change is causing giant heat waves to crawl slower across the globe, thereby baking more people for a longer time with higher temperatures over larger areas.

Heat waves: slower, longer, hotter

Global heat waves have been moving 20% more slowly since 1979, according to a study in Friday's Science Advances, causing more people to endure the heat for a longer duration. The study also reported that the frequency of these heatwaves is 67% more frequent than before. The highest temperatures recorded during these heatwaves are warmer than they were 40 years ago, and the geographical area covered by these heat domes has also expanded.

"Previous studies demonstrated the worsening conditions of heat waves, but this one comprehensively examines more factors, not only concentrating on temperature and area, but also considering the duration of high heat and its pattern of travel across continents," said study co-authors and climate scientists Wei Zhang of Utah State University and Gabriel Lau of Princeton University.

Heatwaves now last four days longer on average

From 1979 to 1983, global heat waves would last eight days on average, but by 2016 to 2020 that was up to 12 days, the study said.

The study stated that longer lasting heat waves hit Eurasia especially hard. It also highlighted that heat waves slowed down the most in Africa. Furthermore, the study noted that North America and Australia experienced the biggest increases in overall magnitude, a measure of temperature and area.

“This paper sends a clear warning that climate change makes heat waves yet more dangerous in more ways than one,” said Lawrence Berkeley National Lab climate scientist Michael Wehner, who wasn't part of the research.

"Just like in an oven, the longer the heat lasts, the more it cooks something. In this case, people are cooking, the co-authors stated."

"Heat waves are traveling slower and even slower, which essentially means that a heat wave is just sitting there and could potentially linger in the region for a longer period," said Zhang. "As time progresses, the resulting negative effects on our human society could increase significantly."

Weather patterns change, heat spreads

The team conducted computer simulations which showed that the change was due to heat-trapping emissions resulting from the burning of coal, oil and natural gas. The study identified the fingerprint of climate change by simulating a world without greenhouse gas emissions and concluded that it could not produce the worsening heat waves we have been observed in the last 45 years.

The study also examines how changes in weather patterns propagate heat waves. Zhang said that atmospheric waves, like the jet stream, which move weather systems along, are weakening. Therefore, they don't move heat waves as quickly from west to east on most continents, but not all.

Several outside scientists praised how Zhang and his colleagues examined heat waves in a big picture way, showing the interaction with weather patterns, their global movement, and especially their slowdown.

Kathy Jacobs, a University of Arizona climate scientist who wasn't part of the study, said this shows how "heat waves evolve in three dimensions and move regionally and across continents rather than looking at temperatures at individual locations".

Jennifer Francis, a scientist at the Woodwell Climate Research Center who did not participate in the study, stated, "Global warming directly causes increasing heat waves, which is one of its most direct consequences. These results put a large exclamation point on that fact."

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