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What is the 'heat dome' phenomenon and why does it matter?

An extended period of hot weather, heat domes can create dangerous conditions for humans, animals and the environments they rely on. But how do they work? And are they really that different from a heat wave?
Davis Bay on B.C.'s Sunshine Coast in October 2022.

In recent years, the term "heat dome" has gained widespread attention due to its association with extreme heat waves that have ravaged various parts of the world.

Some have retroactively applied the term to a heat wave that killed an estimated 10,000 people in the U.S. southern plains during the 1980s. The Dust Bowl conditions that dominated many areas of North America in the 1930s have also been tagged with the moniker.

Meteorologists in the United States had used the term on and off for several years before it went viral during a 2011 heat wave. It would take another decade for the term to solidify in the Canadian meteorological cannon: that year, a record-breaking heat wave consumed British Columbia and the U.S. Pacific northwest, sending temperature records tumbling and leading to hundreds of deaths. 

But while "heat dome" is now commonly heard on both sides of the border and beyond, for many, the weather phenomenon remains poorly understood.

What is a heat dome?

A heat dome refers to a large, high-pressure system that traps hot air underneath it, creating a dome-like structure. 

This stagnant mass of hot air acts as a lid, preventing cooler air from circulating and bringing relief. As a result, the heat becomes trapped within the affected area, leading to soaring temperatures and prolonged heat waves.

The formation of a heat dome is typically associated with a combination of atmospheric and weather patterns. High-pressure systems and sinking air masses, combined with certain geographical factors — such as mountains or bodies of water — contribute to the development of a heat dome. These systems prevent the dispersion of heat and amplify its effects, intensifying the heat wave and turning the affected region into a giant hothouse.

Like anything related to the weather, it's not just local conditions at play. Scientists with the National Oceanic and Atmospheric Association found the main trigger for a heat dome was a strong east-west change in ocean temperatures in the tropical Pacific Ocean a year before a dome forms.

That gradient drives air heated by the ocean to rise over the western Pacific and fall on the ocean’s eastern side. Prevailing winds move the rising hot air over the ocean and northern shifts in the jet stream send it toward North America, where it sinks as a prolonged heat wave.

Impacts of heat domes

Heat domes can have severe impacts on various aspects of life, including public health, infrastructure, and the environment. Prolonged exposure to extreme heat poses significant risks, especially for vulnerable populations such as the elderly, children, and those with pre-existing health conditions such as schizophrenia.

Heat-related illnesses, heat exhaustion, and even fatalities can occur during such heat waves. Additionally, heat domes strain energy resources as air conditioning usage surges, leading to power outages and increased energy demands.

The environment suffers as well, with drought conditions, reduced air quality, and increased wildfire risks often accompanying heat dome events.

2021 North American heat wave

One notable instance of a heat dome occurred in British Columbia in late June 2021. The Metro Vancouver region experienced an unprecedented and prolonged heat wave that shattered temperature records.

In the town of Lytton, B.C., temperatures soared to 49.6 degrees Celsius, an all-time Canadian record. A day later, a wildfire roared through the town, devastating most of its buildings and homes.

This extreme heat had a profound impact on the region, resulting in more than 600 deaths, increased hospitalizations, and strained emergency services.

Wildlife faced its own deadly challenges. Across Western Canada and the U.S. Northwest, baby raptors were observed jumping out of their nests to escape the heat. And on the coast, one expert estimated up to a billion sea creatures cooked to death during the event.

Climate change and heat domes

While heat waves are a natural occurrence, scientists have highlighted the influence of climate change in intensifying these extreme events. Rising global temperatures due to greenhouse gas emissions contribute to the conditions that can generate heat domes. Climate change amplifies the likelihood and severity of heat waves, making them more frequent and intense.

The heat dome that hit B.C. in 2021 was found to have been made 150 times more likely due to climate change.

Under worst-case emission scenarios, the study found climate warming would lead to similar events every five to 10 years by the 2040s, when the world is expected to have ­undergone 2 C of human-induced warming. But even under a less extreme scenario, the results were “pretty similar,” said one researcher.

How people are adapting to the rising threat of heat domes

In response to the increasing frequency and severity of heat waves, communities and governments are implementing various strategies to adapt.

They include developing early warning systems, implementing heat emergency plans, improving urban planning with a focus on green spaces and heat-resilient infrastructure, and promoting public awareness and education regarding heat safety measures.

Some meteorologists warn that heat domes shouldn’t be seen as an independent meteorological phenomenon but rather a generic term to communicate dangerous weather.

“From a societal perspective, we latch on to terms,” said Armel Castellan, a warning preparedness meteorologist with Environment and Climate Change Canada.

“Heat waves, a high-pressure ridge — all of these things are essentially the same idea. A ‘heat dome’ just got attached to that very deadly and tragic event back in 2021.”