Unprecedented heat is popping up in 'hotspots' across the globe

Earth experienced its hottest recorded year in 2023, with temperatures soaring 2.12 degrees Fahrenheit above the 20th-century average, surpassing the previous record set in 2016. The ten warmest years on record have all occurred in the past decade. 

With 2024 already witnessing the hottest summer and single hottest day, it is on track to set yet another alarming record.

Extreme regional heat waves

While the steady increase in global average temperatures may not surprise everyone, a striking new phenomenon is emerging: certain regions are experiencing repeated 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 worldwide map of the regions experiencing unprecedented heat, which appear on every continent except Antarctica like vast, alarming hotspots. 

In recent years, these heat waves have resulted in tens of thousands of deaths, devastated crops and forests, and ignited catastrophic wildfires.

“The large and unexpected margins by which recent regional-scale extremes have broken earlier records have raised questions about the degree to which climate models can provide adequate estimates of relations between global mean temperature changes and regional climate risks,” the authors explained.

Decades of heat waves

“This is about extreme trends that are the outcome of physical interactions we might not completely understand,” said lead author Kai Kornhuber, an adjunct scientist at the Columbia Climate School’s Lamont-Doherty Earth Observatory. “These regions become temporary hothouses.” 

The researchers examined heat waves over the past 65 years. It identifies areas where extreme heat is accelerating much faster than moderate temperatures, often resulting in record-breaking maximum temperatures by astonishing amounts.

For example, a nine-day heat wave that struck the U.S. Pacific Northwest and southwestern Canada in June 2021 shattered daily records in some locations by 30 degrees Celsius (54 degrees Fahrenheit). 

This included Canada’s highest ever recorded temperature of 121.3 F in Lytton, British Columbia. Tragically, the town burned to the ground the next day in a wildfire fueled largely by dried vegetation from the extreme heat. 

Regions affected by unprecedented heat

In Oregon and Washington state, hundreds of people died from heat stroke and other health conditions. These extreme heat waves have predominantly occurred in the last five years, though some happened in the early 2000s or earlier. 

The most affected regions include populous areas of central China, Japan, Korea, the Arabian Peninsula, eastern Australia, and scattered parts of Africa. 

Other impacted areas include Canada’s Northwest Territories and 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, though they are not among the most extreme areas.

Europe’s vulnerability to unprecedented heat 

According to the report, the most intense and consistent signals come from northwestern Europe, where successive heat waves contributed to approximately 60,000 deaths in 2022 and 47,000 deaths in 2023. 

These events occurred across Germany, France, the United Kingdom, the Netherlands, and other countries. In recent years, the hottest days are warming twice as fast as average summer temperatures in this region. 

Europe is particularly vulnerable because, unlike places like the United States, few people have air conditioning due to traditionally milder climates. 

The heat waves have continued; as recently as this September, new maximum temperature records were set in Austria, France, Hungary, Slovenia, Norway, and Sweden.

Researchers refer to these statistical trends as “tail-widening” – the unusual occurrence of temperatures at the extreme upper end, or beyond, anything expected from simple upward shifts in mean summer temperatures. 

However, this phenomenon is not universal; the study shows that maximum temperatures in many other regions are actually lower than what models would predict. 

These areas include vast parts of the north-central United States and south-central Canada, interior regions of South America, much of Siberia, northern Africa, and northern Australia. While heat is increasing in these regions, the extremes are rising at similar or lower rates than changes in average temperatures would suggest.

Causes of extreme heat events

Overall rising temperatures make heat waves more likely in many cases, but the exact causes of these extreme heat events are not entirely clear. In Europe and Russia, a previous study led by Kornhuber attributed heat waves and droughts to fluctuations in the jet stream – a fast-moving air current that circles the northern hemisphere. 

Traditionally confined to a narrow band due to the temperature difference between the frigid Arctic and warmer southern regions, the jet stream is becoming destabilized as the Arctic warms more rapidly than other parts of the Earth. 

This destabilization leads to the formation of Rossby waves, which draw hot air from the south and stall it over temperate regions not accustomed to extreme heat for prolonged periods.

However, this hypothesis does not explain all extreme events. A study of the deadly 2021 Pacific Northwest and southwestern Canada heat wave, led by Lamont-Doherty graduate student Samuel Bartusek (also a co-author on the latest paper), identified a combination of factors. 

Some were linked to long-term climate change, while others appeared to be due to chance. The study noted a disruption in the jet stream similar to the Rossby waves affecting Europe and Russia. 

Decades of rising temperatures

The researchers also found that decades of gradually rising temperatures had dried out regional vegetation, so when intense heat arrived, plants had less water to evaporate into the air – a process that helps moderate temperatures. 

Another factor was a series of smaller-scale atmospheric waves that transported heat from the Pacific Ocean’s surface eastward onto land. As in Europe, few people in this region have air conditioning, likely increasing the death toll.

The heat wave “was so extreme, it’s tempting to apply the label of a ‘black swan’ event, one that can’t be predicted,” Bartusek said. “But there’s a boundary between the totally unpredictable, the plausible, and the totally expected that’s hard to categorize. I would call this more of a grey swan.”

Increasing human toll from unprecedented heat

Even in wealthy nations like the United States, excessive heat remains the leading cause of weather-related deaths, surpassing hurricanes, tornadoes, and floods combined. 

A study released this past August reported that the annual death rate has more than doubled since 1999, reaching 2,325 heat-related deaths in 2023. 

This alarming trend has led to calls for naming heat waves, similar to hurricanes, to increase public awareness and encourage government preparedness.

“Due to their unprecedented nature, these heat waves are usually linked to very severe health impacts, and can be disastrous for agriculture, vegetation, and infrastructure. We’re not built for them, and we might not be able to adapt fast enough,” Kornhuber concluded.

The study is published in the journal Proceedings of the National Academy of Sciences.

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