Record-high temperatures in western US due to ‘heat domes’: What is the phenomenon?

A heat dome is a weather phenomenon where a high-pressure system in the atmosphere traps warm air like a lid on a pot, for an extended period of time.

Fernando Toledo wipes his face with a cold towel during a period of excessive heat in Calexico, California, US, July 7, 2024. REUTERS

Written by: Alind Chauhan

3 min readNew DelhiJul 11, 2024 12:07 PM IST First published on: Jul 10, 2024 at 07:04 PM IST

The entire western United States has come under the grip of a sweltering heatwave, which began last week. Nearly 75 million people are under heat alerts, and temperature records are tumbling.

The worst affected is California, where at least a dozen cities broke all-time high-temperature records. For instance, between Friday (July 5) and Saturday (July 6), mercury soared never-seen-before 48.33 degree Celsius and 47.22 degree Celsius in Redding, a city in Northern California, and Ukiah, north of San Francisco, respectively. Palm Springs, in Southern California, touched a record-breaking high of 51.11 degree Celsius.

The scorching temperatures and dry conditions are a result of a heat dome centred over California.

Here is a look at what a heat dome is, how it is tied to the behaviour of the jet stream, and how climate change impacts heat domes.

What is a heat dome?

A heat dome is a weather phenomenon where a high-pressure system in the atmosphere traps warm air like a lid on a pot, for an extended period of time. As the warm air is not able to rise upward, the sky remains clear — clouds are formed under the opposite circumstances as the rising warm air cools down, and the water in it condenses out.

The high-pressure system allows more sunlight to reach the earth, which results in more warming and drying of soil. This leads to less evaporation and reduces the likelihood of the formation of rain clouds. The longer the heat dome stays in one place, the warmer conditions can get with every passing day. While heat domes cause heatwaves, they can occur without heat domes as well.

What is the role of the jet stream?

A heat dome’s formation is tied to the behaviour of the jet stream — an area of fast-moving air high in the atmosphere that usually helps move weather systems along the Earth’s surface.

Typically, the jet stream has a wave-like pattern that keeps moving from north to south and then north again. When these waves get bigger and elongated, they move slowly and sometimes can become stationary. This is when a high-pressure system gets stuck in place, and leads to the occurrence of a heat dome.

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How is climate change impacting heat domes?

Scientists are still debating over how climate change is impacting the blocking weather events that cause heat domes. However, they have ascertained that rising global temperatures have made heat domes larger and more intense.

A 2021 study carried out by an international team of 27 climate researchers, who were part of the World Weather Attribution, found that searing temperatures recorded during the heat dome in Canada, which occurred in June that year, “would have been virtually impossible without the influence of human-caused climate change”.

Another study, published in the journal Nature 2023, indicated that the intensity of heat domes is outpacing the rate of global warming — which means that climate change is fuelling their intensity.

“The intensities of hot extremes associated with… heat dome-like atmospheric circulations increase faster than background global warming in both historical change and future projection”, the study said.