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In 2023, Earth experienced its hottest year on record, with temperatures jumping 2,12 degrees Fahrenheit above the 20th century average, surpassing the previous record set in 2016. The ten warmest years were in the last decade. With 2024 already the hottest summer and one of the hottest days ever, it is on track to set another alarming record.
Extreme regional heat
While the steady increase in global average temperatures may not come as a surprise to everyone, a striking new phenomenon is emerging: certain regions experience recurring heat waves so extreme that they far exceed what any global warming model can predict or explain.
In a new study, researchers have created the first global map of regions experiencing unprecedented heat, which is appearing on every continent except Antarctica as huge, alarming hotspots. In recent years, heat waves have killed tens of thousands, devastated crops and forests, and sparked catastrophic wildfires.
"The large and unexpected extents by which recent extreme events on a regional scale have broken previous records have raised questions about the extent to which climate models can provide adequate estimates of the links between global mean temperature changes and regional climate risks," the authors explained.
A decade of heat
"These are extreme trends that are the result of physical interactions that we may not fully understand," said lead author Kai Kornhuber, a research scientist at the Lamont-Dougherty Earth Observatory at Columbia's Climate School. "These regions become temporary hothouses."
Researchers have studied heat waves over the past 65 years. It identifies areas where extreme heat accelerates much faster than moderate temperatures, often resulting in record maximum temperatures of spectacular magnitudes. For example, a nine-day heat wave that hit the US Pacific Northwest and the Canadian Southwest in June 2021 broke daily records in some locations by 30 degrees Celsius (54 degrees Fahrenheit).
This included the highest temperature ever recorded in Canada of 121,3 F in Lytton, British Columbia. Unfortunately, the next day, the town burned to the ground in a forest fire, mostly caused by the withered vegetation from the intense heat.
Regions affected by unprecedented heat
In the states of Oregon and Washington, hundreds of people died from heat stroke and other diseases. These extreme heat waves have mostly occurred within the past five years, although some have occurred in the early 2000s or earlier. The most affected regions include densely populated areas of central China, Japan, Korea, the Arabian Peninsula, eastern Australia and scattered parts of Africa.
Other areas affected include the Northwest Territories of Canada and the High Arctic Islands, northern Greenland, the southern tip of South America, and scattered regions of Siberia. Parts of Texas and New Mexico also appear on the map, although they are not among the most extreme areas.
Vulnerability of Europe to unprecedented heat
According to the report, the most intense and consistent signals come from northwestern Europe, where successive heat waves caused an estimated 60 deaths in 000 and 2022 deaths in 47.
These events took place in Germany, France, Great Britain, the Netherlands and other countries. In recent years, the hottest days have warmed twice as fast as average summer temperatures in the region. Europe is particularly vulnerable because, unlike places like the United States, few people have air conditioning because of the traditionally mild climate. Heat waves continue; As recently as this September, new maximum temperature records were set in Austria, France, Hungary, Slovenia, Norway and Sweden.
The researchers call these statistical trends "tail extension" -- the unusual occurrence of temperatures at or even beyond the extreme upper limit of what would be expected from simple fluctuations in average summer temperatures. However, this phenomenon is not universal; the study shows that maximum temperatures in many other regions are actually lower than the models predict.
These areas include large parts of the north-central United States and south-central Canada, interior regions of South America, most of Siberia, northern Africa, and northern Australia. While heat is increasing in these regions, extreme values are increasing at the same or lower rates than would be predicted by changes in average temperatures.
Causes of extreme heat
A general increase in temperatures makes heat waves more likely in many cases, but the exact causes of these extreme heat events are not entirely clear. In Europe, previous research led by Kornhuber linked heat waves and droughts to fluctuations in the jet stream, a fast-moving stream of air that rotates around the northern hemisphere.
Traditionally confined to a narrow band due to the temperature difference between the cold Arctic and warmer southern regions, the jet stream is destabilizing as the Arctic warms faster than other parts of the Earth. This destabilization leads to the formation of Rossby waves, which draw in hot air from the south and trap it over temperate regions that are not used to extreme heat for long periods of time.
However, this hypothesis does not explain all extreme phenomena. A study of the deadly heat wave in the Pacific Northwest and southwestern Canada in 2021 by Lamont-Doherty graduate student Samuel Bartusek (also a co-author of the final paper) found a combination of factors. Some were linked to long-term climate change, while others appeared to have occurred by chance. The study noted a jet stream disturbance similar to Rossby waves affecting Europe.
A decade of warming
The researchers also found that decades of gradually rising temperatures dried out the region's vegetation, so when extreme heat struck, plants had less water to evaporate into the air, a process that helps lower temperatures. Another factor was a series of smaller atmospheric waves that carried heat from the surface of the Pacific Ocean eastward onto land. As in Europe, few people in the region have air conditioning, which likely increases the number of deaths.
The heat wave "was so extreme that it's tempting to call it a black swan event, which is impossible to predict," Bartusek said. “But there is a line between completely unpredictable, believable and completely expected, which is difficult to classify. I would rather call it a gray swan."
Increase in human casualties from unprecedented heat
Even in wealthy countries like the United States, excessive heat remains the leading cause of weather-related deaths, surpassing hurricanes, tornadoes and floods combined. A study published last August found that the annual death rate has more than doubled since 1999, reaching 2325 heat-related deaths in 2023. The alarming trend has led to calls for heat waves to be labeled hurricane-like to raise public awareness and encourage government preparedness.
"Due to their unprecedented nature, these heat waves are usually associated with very serious health consequences and can be catastrophic for agriculture, vegetation and infrastructure. We are not built for them, and we may not be able to adapt fast enough,” Kornhuber concluded. The study is published in the journal Proceedings of the National Academy of Sciences.
