Unprecedented heat waves occur in hot spots around the world

Earth recorded its hottest year in 2023, with temperatures rising 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 last decade.

With 2024 already set to have its hottest summer and hottest day yet, it is on track to set another alarming record.

Extreme regional heat waves

While the sustained rise in global average temperatures may not surprise everyone, a startling new phenomenon is emerging: some regions are experiencing repeated heat waves so strong 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 regions experiencing unprecedented heat, which are emerging as huge, worrying hot spots on every continent except Antarctica.

In recent years, these heat waves have killed tens of thousands of people, destroyed crops and forests, and sparked catastrophic wildfires.

“The large and unexpected extent to which recent regional-scale extreme events have broken previous records has raised questions about the extent to which climate models can provide adequate estimates of the relationship between global mean temperature changes and regional climate risks,” the authors explained.

Decades of heat waves

“We’re talking about extreme trends that result from physical interactions that we may not fully understand,” said lead author Kai Kornhuber, a postdoctoral fellow at Columbia Climate School’s Lamont-Doherty Earth Observatory. “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 in astounding numbers.

For example, the nine-day heat wave that hit the US Pacific Northwest and southwestern Canada in June 2021 broke daily records in some places by 30 degrees Celsius (54 degrees Fahrenheit).

This includes the highest temperature ever recorded in Canada – 121.3 F in Lytton, British Columbia. Unfortunately, the next day the town burned to the ground in a forest fire caused mainly by dry vegetation due to the intense heat.

Regions affected by unprecedented heat

In Oregon and Washington, hundreds of people died from heatstroke and other illnesses. These extreme heat waves have occurred primarily in the last five years, although some occurred in the early 2000s or earlier.

The worst-affected regions include densely populated areas of central China, Japan, Korea, the Arabian Peninsula, eastern Australia and parts of Africa.

Other affected 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, although they are not among the most extreme areas.

Europe’s vulnerability to unprecedented heat

The most intense and consistent signals come from northwestern Europe, where successive heat waves caused an estimated 60,000 deaths in 2022 and 47,000 deaths in 2023, according to the report.

These events took place in Germany, France, Great Britain, the Netherlands and other countries. In recent years, the hottest days have warmed up twice as fast as average summer temperatures in the region.

Europe is particularly vulnerable because, unlike places like the US, few people have air conditioning due to its traditionally milder climate.

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

Researchers call these statistical trends “tail spreads”—an unusual occurrence of temperatures at or beyond the extreme upper level that would be expected from a simple increase in average summer temperatures.

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

These areas include large parts of the north-central United States and south-central Canada, inland regions of South America, much of Siberia, northern Africa, and northern Australia. Although heat is increasing in these regions, extreme temperatures are increasing at the same or lower rates than changes in average temperatures would suggest.

Causes of extreme heat

A general increase in temperature makes heat waves more likely in many cases, but the exact causes of these extreme heat events are not entirely clear. In Europe and Russia, previous research led by Kornhuber has linked heat waves and droughts to fluctuations in the jet stream, a fast-moving air current that circles the northern hemisphere.

Traditionally limited to a narrow band by temperature differences between the cold Arctic and warmer southern regions, the jet stream is becoming destabilized as the Arctic warms faster than other parts of the Earth.

This destabilization results in the formation of Rossby waves, which draw hot air from the south and trap it in temperate regions not accustomed to extreme heat for long periods of time.

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

Some of these were linked to long-term climate change, while others appeared to be coincidental. The study notes a jet stream disruption similar to Rossby waves affecting Europe and Russia.

Decades of rising temperatures

The researchers also found that decades of gradually rising temperatures had caused regional vegetation to dry out, so when extreme heat struck, 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 carried heat from the surface of the Pacific Ocean eastward to land. As in Europe, few people in this region have air conditioning, which likely increases the death toll.

The heat wave “was so severe that it is tempting to apply the label of a ‘black swan,’ an event that is impossible to predict,” Bartusek said. “But there is a line between the completely unpredictable, the plausible and the completely expected that is difficult to categorize. I would call it more of a gray swan.”

Increase in casualties due to 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 in August this year found 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 hurricane-like heatwaves to be named to increase public awareness and government preparedness.

“Due to their unprecedented nature, these heat waves are typically associated with very serious health consequences and can have catastrophic impacts on agriculture, vegetation and infrastructure. We are not built for them and may not be able to adapt quickly enough,” concluded Kornhuber.

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

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