A heat dome is a weather event that happens when very hot air becomes trapped in the atmosphere, like being covered by a lid or cap. This occurs when high-pressure air stays in one place for an unusual amount of time, stopping air from rising and rain from forming. This trapping of hot air can be influenced by factors such as unusual ocean temperatures and the effects of a La Niña. The slow movement of upper-level air patterns is called an Omega block by meteorologists.

The term "heat dome" is sometimes used in the media to describe any heat wave, but heat waves are not always caused by this type of high-pressure system. The term is also used in discussions about urban heat islands, which are areas in cities that become much hotter than surrounding regions.

Characteristics

Heat domes are usually found in areas with few clouds and clear skies. These conditions let sunlight reach Earth's surface without being blocked, which increases temperatures.

Heat domes cover large areas where the air pressure is higher than in nearby regions. This high pressure acts like a cover over the atmosphere, trapping warm air near the ground and keeping it there for long periods.

Heat domes allow the most sunlight to reach Earth's surface, which leads to the greatest amount of heating.

Creation

Heat domes can form during calm and dry summer weather when a large area of warm air accumulates. High pressure in the Earth's atmosphere pushes this warm air downward. As the air is squeezed into a smaller space, its temperature rises. When the warm air tries to rise, the high pressure above acts like a dome, pressing the air back down and making it even hotter. This creates higher pressure beneath the dome.

In 2021, a heat dome formed in the Northwest because a high-pressure system remained in place. This system raised local temperatures, stopped cooling ocean winds from reaching the area, and prevented clouds from forming. Without clouds to block sunlight, the sun heated the air and land continuously. The warm air was then pushed back down by the high-pressure system, creating a cycle that kept temperatures rising.

Warmer sea surface temperatures in the Northern Pacific, especially near Washington, Oregon, and British Columbia, help create high-pressure systems in the atmosphere. These systems can lead to the development of heat domes.

Research shows that human-caused climate change increases the likelihood of heat domes forming. Higher atmospheric temperatures make heat domes more common. When heat domes occur, they raise overall temperatures, which can worsen climate change over time.

Effects

Heat domes happen when air doesn’t move much, making air quality problems worse. This leads to more smog and pollution. Heat domes can make heat waves stronger by working with other weather systems, like areas where warm and cool air meet. They also help cause droughts by speeding up evaporation and lowering soil moisture. In places like California’s Central Valley, heat domes make droughts worse by increasing how quickly water leaves crops and plants.

Past heat domes have caused widespread tree damage, mainly because of strong sunlight. Leaves can burn from the heat, and over time, plants that can survive high temperatures have developed.

Heat domes increase the stress on living things in intertidal areas, which are places where the ocean meets the land. This stress has caused deaths of sea animals during the 2021 North American Heat Dome.

Heat domes have made people more worried about climate change. For example, people in British Columbia showed higher levels of concern about climate change after the 2021 heat dome.

Heat domes increase the risk of deaths in communities. People who are more likely to die from heat domes include those who are already vulnerable or have limited access to air conditioning.

Examples

The 2025 European heatwave was caused by a heat dome, and human-caused climate change likely played a role.

The 2021 Western North America heat dome was unusually strong and long-lasting, causing important effects on society, such as widespread power outages and more wildfires.

This event caused agricultural losses of more than $600 million in the Pacific Northwest alone, damaged fruit crops, and led to many animals dying. This affected food supplies in the region for several months. It showed the need to address climate change to reduce the number and severity of such events. Reducing greenhouse gas emissions and using strategies to manage heat are important steps to lower the frequency of extreme heat events in 2021.

In 2021, a record-breaking heat dome in British Columbia caused 595 deaths, the highest number for similar weather events. Many homes in the Vancouver area do not have air conditioning, making people more likely to suffer from heat-related illnesses like heat exhaustion and heat stroke. A study on this event highlights the importance of public health efforts, such as increasing access to air conditioning and creating more green spaces in cities.

A long-lasting heat dome in 2010 caused extensive wildfires, crop failures, and higher death rates during the Russian heatwave. The effects of this event, including economic and social challenges, had global impacts, showing how weather patterns and agricultural markets are connected across regions.

• 1936 North American heat wave
• 2012 North American heat wave
• 2018 North American heat wave
• 2010 Russian heatwave
• 2021 British Columbia wildfires
• 2021 Western North America heat wave
• 2023 Western North America heat wave
• 2023 South America heat wave

Future

Research suggests that stationary waves moving around North America may increase in the future after heat domes form. These waves are connected to extreme heat events, meaning such events could happen more often. Studies show that heat domes usually do not occur frequently. However, growing concern about climate change suggests that heat domes might become more common over time.

Ways to reduce the effects of heat domes include urban planning, public health programs, and working with communities. Strategies involve creating more green spaces, using cool roofs, and improving air flow in cities. Public agencies help protect people at higher risk by using methods such as heat health warning systems, tracking data, providing cooling centers, managing water supplies, and addressing climate change. Educational efforts also help people understand how to stay safe during heat events, which makes other solutions more effective.