Unexplained heat wave “hotspots” appear around the world

Regions where observed heat waves exceed climate model trends. The darkest red boxed area is the most extreme. Less red and orange outperform the model, but not by much. The yellow almost matches the model, but the green and blue are lower than what the model projects. Credit: Kornhuber et al., taken from PNAS 2024
The hottest year on record was 2023, which was 2.12°F above the 20th century average. This surpassed the previous record set in 2016. So far, the 10 hottest annual average temperatures have been recorded in the past decade. And 2024 is set to set even more records, with the hottest summer and hottest days yet.
All of this may not be breaking news to everyone, but amidst this rise in average temperatures, a surprising new phenomenon is emerging. Certain regions are repeatedly experiencing extremely extreme heat waves, far beyond what any model of global warming can predict. Or explain.
A new study published in the Proceedings of the National Academy of Sciences provides the first global map of such regions, which appear like giant angry patches of skin on every continent except Antarctica. In recent years, these heatwaves have killed tens of thousands of people, destroyed crops and forests, and sparked devastating wildfires.
“The large and unexpected difference in recent regional-scale extreme events breaking previous records raises questions about how well climate models can estimate the relationship between global mean temperature change and regional climate risks. ”, the study said.
“This is about extreme trends that are the result of physical interactions that we may not fully understand,” said lead author and part-time scientist at Columbia Climate School’s Lamont-Doherty Earth Observatory. said Mr. Kai Kornhuber. “These areas become temporary greenhouses.” Kornhuber is also a senior researcher at the International Institute for Applied Systems Analysis in Austria.
The study examines heat waves over the past 65 years and identifies areas where extreme heat has significantly accelerated compared to milder temperatures. As a result, maximum temperatures are repeatedly broken by unusual and sometimes surprising amounts.
For example, a nine-day wave that hit the U.S. Pacific Northwest and southwestern Canada in June 2021 broke daily temperature records by 30 °C (54 °F) in some regions. This included the highest temperature ever recorded in Canada, 121.3 degrees Fahrenheit, in Lytton, British Columbia. The town was gutted the next day by a wildfire caused primarily by drying out vegetation due to the unusually hot weather. Hundreds of people died from heatstroke and other health conditions in Oregon and Washington.
These extreme heat waves have mainly occurred in the past five years or so, but some have occurred since the early 2000s or earlier. The worst-hit areas include populous central China, Japan, South Korea, the Arabian Peninsula, eastern Australia, and scattered areas of Africa.
Others include Canada’s Northwest Territories and its high arctic islands, northern Greenland, the southern tip of South America, and scattered areas of Siberia. Areas of Texas and New Mexico are visible on the map, but not at the extremes.


Researchers have identified meanderings in the Northern Hemisphere’s jet stream that could suck in hot air from the south, triggering massive heat waves across large swathes of North America and Eurasia. This image is from a 2020 study. Credit: Kornhuber et al., Nature Climate Change, 2020
The report said the strongest and most consistent signal came from northwestern Europe, where a series of heatwaves killed around 60,000 people in 2022 and 47,000 in 2023. These occurred in Germany, France, the United Kingdom, the Netherlands, and other countries. .
Discover the latest in science, technology and space with over 100,000 subscribers who use Phys.org as their daily source of information. Sign up for our free newsletter to receive daily or weekly updates on breakthroughs, innovations, and important research.
Temperatures here on the hottest days of the year have risen twice as fast as average summer temperatures in recent years. This region is particularly vulnerable in part because, unlike in places like the United States, few people have air conditioning, as traditionally there was little need for it. The trend continues. New temperature records were also set in September this year in Austria, France, Hungary, Slovenia, Norway and Sweden.
Researchers call this statistical trend “tail broadening.” That is, an abnormal occurrence of temperatures far above or above what would be expected from a simple increase in average summer temperatures. However, this phenomenon is not happening everywhere. This study shows that maximum temperatures in many other regions are actually lower than what models predict.
These include large areas of the north-central United States and south-central Canada, the interior of South America, much of Siberia, northern Africa, and northern Australia. Heat is also increasing in these regions, but extreme heat is increasing at the same rate or slower than the average change indicates.
Rising overall temperatures often make heat waves more likely, but the causes of heat waves are not entirely clear. In Europe and Russia, early research led by Kornhuber blamed heat waves and droughts on fluctuations in the jet stream, a fast-moving river of air that constantly orbits the Northern Hemisphere.
Due to historically frigid temperatures in the far north, surrounded by much warmer temperatures further south, the jet stream is generally confined to a narrow area. But the Arctic is warming much faster on average than most other parts of the planet, and this appears to be destabilizing the jet stream, creating so-called Rossby waves that draw hot air in from the south and keep it in the temperate zone. is. Areas that do not typically experience extreme heat for days or weeks at a time.
This is just one hypothesis and does not seem to explain all extreme phenomena. A study led by Lamont-Doherty graduate student Samuel Bartusek (who is also a co-author of the latest paper) on the deadly 2021 Pacific Northwest/southwestern Canada heatwave shows that multiple factors converged. It turned out that Some appear to be related to long-term climate change, while others appear to be related by chance.
The study identified jet stream turbulence similar to Rossby waves, which are thought to affect Europe and Russia. Additionally, as temperatures have continued to rise slowly over the decades, the area’s vegetation has become drier, so during intense heat waves, plants have less moisture to evaporate into the air, causing heat waves to evaporate. It was also found that this is a process that alleviates the
The third factor was a series of small atmospheric waves that collected heat from the Pacific surface and transported it eastward to land. As in Europe, very few people in this region have air conditioning. This is because air conditioning is generally not needed, which probably increased the number of deaths.
The heatwave was “so extreme that it’s tempting to label it an unpredictable ‘black swan’ event,” Bartusek said. “But there’s a line between what’s completely unpredictable, what’s plausible, and what’s completely expected that’s hard to categorize. I call it the gray swan.”
Although the wealthy United States is better prepared than many other regions, excessive heat still kills more people than all other weather-related causes, including hurricanes, tornadoes, and flooding combined. . According to a study published in August this year, the annual death rate has more than doubled since 1999, with 2,325 heat-related deaths expected in 2023. As a result, there have been recent calls for heat waves to be named in the same way as hurricanes. Raise public awareness and urge the government to prepare.
“Due to their unprecedented nature, these heatwaves are typically associated with very serious health effects and can have devastating effects on agriculture, vegetation and infrastructure,” Kornhuber said. said. “We may not be able to adapt quickly enough because we are not built for them.”
The study was also co-authored by Richard Seeger and Ming-Fang Ting of the Lamont-Doherty Earth Observatory and HJ Schellnhuber of the International Institute for Applied Systems Analysis.
Further information: Kai Kornhuber et al, “Global emergence of regional heatwave hotspots outpaces climate model simulations,” Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2411258121
Provided by Columbia Climate School
Source: Unexplained heat wave ‘hotspots’ are emerging around the world (November 26, 2024) from https://phys.org/news/2024-11-unexplained-hotspots-globe.html 2024 Retrieved on November 26th
This document is subject to copyright. No part may be reproduced without written permission, except in fair dealing for personal study or research purposes. Content is provided for informational purposes only.