Mysterious Heat-Wave Hotspots Emerge Worldwide, Leaving Scientists Puzzled
Record-Breaking Temperatures and the Rise of Extreme Heat Events
2023 holds the record as the Earth's hottest year, with an average temperature 2.12°F above the 20th-century norm. This exceeded the previous high set in 2016. Remarkably, the past decade has seen the top 10 warmest years ever recorded. With the hottest summer and single day in history, 2024 is poised to break new records.
The Emergence of Extreme Heat-Wave Hotspots
This may not come as a surprise to all, but amid the steady rise in average temperatures, a striking anomaly has emerged: certain regions are experiencing recurring heat waves so severe they surpass the predictive scope of current global warming models.
Mapping the Hotspots
Researchers in the Proceeding of the National Academy of Sciences have published the first global map pinpointing regions of recurrent extreme heat waves, seen across every continent except Antarctica as prominent, alarming hotspots. These heat waves have caused extensive loss of life, destroyed agriculture and forests, and triggered devastating wildfires.
The Role of Climate Models in Predicting Extreme Heat
Unprecedented Heat Wave Records
The study points out that the significant and surprising margins by which recent regional extremes have broken historical records have raised important questions about the effectiveness of climate models in predicting the connections between global temperature changes and regional climate vulnerabilities.
Lead author Kai Kornhuber, an adjunct scientist at Columbia Climate School's Lamont-Doherty Earth Observatory, explained, "These extreme trends arise from physical interactions we may not fully comprehend. These regions turn into temporary hothouses." Kornhuber is also a senior research scholar at the International Institute for Applied Systems Analysis in Austria.
Focusing on heat waves from the past 65 years, the study identifies regions where extreme heat is increasing far faster than more moderate temperatures. As a result, maximum temperatures are frequently shattered, with some exceeding previous records by remarkable, and at times surprising, amounts.
The 2021 Heat Wave in North America
For example, a nine-day heat wave that struck the U.S. Pacific Northwest and southwestern Canada in June 2021 shattered daily temperature records in some areas by as much as 30°C (54°F). This included Canada's highest-ever recorded temperature of 121.3°F in Lytton, British Columbia. Tragically, the town was destroyed by a wildfire the following day, Fueled by the drying effects fo the extreme heat. In Oregon and Washington, hundreds of fatalities occurred due to heatstroke and related health issues.
A Decade of Intense Heat
While some extreme heat waves have occurred as early as the 2000s or prior, the most significant heat events have predominantly taken place over the last five years. The hardest-hit regions include densely populated areas in central China, Japan, Korea, the Arabian Peninsula, eastern Australia, and various parts of Africa.
Hard-Hit Regions
Other affected regions include Canada's Northwest Territories and High Arctic islands, northern Greenland, the southern tip of South America, and scattered parts of Siberia. While areas of Texas and New Mexico are included, they are not among the most extreme locations.
Heat Waves in Northwestern Europe
According to the report, the strongest and most sustained signal comes from northwestern Europe, where successive heat waves resulted in around 60,000 deaths in 2022 and 47,000 in 2023.
Unique Vulnerabilities
These deaths occurred throughout Germany, France the United Kingdom, the Netherlands, and other countries.
In recent years, the hottest days of the year in this region have warmed at twice the rate of the average summer temperatures. The area is particularly vulnerable, partly because, unlike regions such as the United States, air conditioning is rare, as it was historically unnecessary. These heat waves have persisted, with new temperature records being set as recently as this September in Austria, France, Hungary, Slovenia, Norway, and Sweden.
Tail-Widening: The Statistical Trend
The researchers refer to the observed statistical trends as 'tail-widening,' describing the unusual rise in temperatures at the extreme upper end, which goes beyond what would be anticipated from a simple increase in average summer temperatures. However, this phenomenon is not universal; the study reveals that maximum temperatures in many other regions are actually lower than what models would predict.
Areas with Lower-Than-Expected Heat Increases
These regions include large parts of the north-central United States and south-central Canada, the interior of South America, much of Siberia, northern Africa, and northern Australia. While heat is rising in these areas as well, the extremes are increasing at a pace similar to or slower than what would be expected based on average temperature changes.
Potential Causes of Extreme Heat Events
The Role of the Jet Stream
Rising temperatures contribute to the increased likelihood of heat waves in many instances, yet the exact causes behind these extreme heat events remain unclear. A previous study in Europe and Russia, led by Kornhuber, attributed heat waves and droughts to disturbances in the jet stream, a fast-moving air current that circulates the northern hemisphere.
Historically confined by the frigid temperatures of the far north and the warmer air to the south, the jet stream typically follows a narrow path. However,the Arctic is warming significantly faster than most other regions of the world, which seems to be destabilizing the jet stream. This instability leads to the formation of Rossby waves, which pull hot air from the south and trap it in temperate areas that usually do not experience prolonged extreme heat.
This hypothesis is just one of several, and it does not appear to account for all the extreme events. A study of the deadly 2021 heat wave in the Pacific Northwest and southwestern Canada, led by Lamont-Doherty graduate student Samuel Bartusek (also a co-author of the current paper), found that multiple factors were at play. Some seemed related to long-term climate change, while others were more coincidental.
A third element was a series of smaller atmospheric waves that took heat from the Pacific Ocean and directed it eastward over land. Much like Europe, the region's relatively low use of air conditioning, due to its historically temperate climate, likely contributed to the high number of fatalities.
The heat wave was so severe that it could be classified as a 'black swan' event, one that defies prediction, according to Bartusek. However, he adds, there's a fine line between what is completely unpredictable, plausible, and foreseeable, making it difficult to categorize. 'I would label this more as a gray swan,' he said.
The Ongoing Impact of Heat Waves
Heat Wave Death Toll and Awareness
While the United States, with its resources, is better prepared than many nations, excessive heat continues to cause more deaths annually than all other weather-related events, including hurricanes, tornadoes, and floods. A recent study from August shows that the heat-related death rate has more than doubled since 1999, with 2,325 fatalities in 2023. This has led to suggestions that heat waves be named, akin to hurricanes, to rise awareness and encourage government action.
According to Kornhuber, these heat waves, due to their unparalleled intensity, are typically associated with severe health consequences and can wreak havoc on agriculture, vegetation, and infrastructure. "Our systems are not designed to withstand such extremes, and our ability to adapt may not be fast enough," he warned.
The study was co-authored by Richard Seager and Mingfang Ting from Lamont-Doherty Earth Observatory, along with H.J. Schellnhuber from the International Institute for Applied Systems Analysis.
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