Current extreme temperatures are related to a ‘heat dome’, but what exactly are these weather phenomena and how are they formed?
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The term ‘heat wave’ has become an increasingly familiar term in news headlines in recent years, as countries battle rising temperatures amid climate change.
The last decade – between 2011 and 2020 – has been the warmest on record, driven primarily by human-induced greenhouse gas emissions. Now, the Earth is between 1.34C and 1.41C warmer than it was in the pre-industrial era.
In 2024 the world saw a spate of record-breaking temperatures – including a scorching 48.8C recorded in Sicily – which meteorologists attributed to a phenomenon known as a ‘heat dome’ instead.
This summer, extreme temperatures expected in the UK in the coming days are once again related to a heat dome over the nation.
So what’s the difference between heat domes and heat waves? And are heat domes getting worse in the same way that heat waves are?
What are heat domes?
A heat dome is formed when an area of high pressure in the atmosphere remains over the same region for a prolonged period of time, acting like a lid on a pot. As a result, hot air is caught underneath the pressure system and cool air cannot enter, creating the aptly named heat dome.
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The hot air in a heat dome will try to enter the atmosphere, but pressure will either cause it to subside or sink – a process which further increases air temperature. Then, the ground warms and loses moisture, making it more likely to increase in temperature. As such, a cycle develops, and until the high-pressure area moves, the mercury will continue to rise.
The weather phenomenon also suppresses cloud cover and rainfall, which further exacerbates the high temperatures they bring. That’s because sunlight can hit the Earth’s surface more easily.
An average heat dome will last for up to four days, but some can persist for around two weeks, and on rare occasions, for even longer. Examples of heat domes in recent years include those in June 2024 in the US, along with the scorching temperatures brought about by a heat dome in July 2024 in Western Europe during the Olympic Games.
The UK is currently bracing itself for a heat dome, bringing high temperatures and weather warnings as thermometers are set to reach 30 to 35C in places. Already, the nation has seen scorching days, with the hottest day of the year so far recorded on 1 July in Faversham, Kent, at 35.8C.
Are they different from heat waves?
The difference between the terms ‘heat wave’ and ‘heat dome’ varies between meteorologists, scientists and other experts.
Some scientists believe the two terms should be clearly demarcated, with the American Meteorological Society adding ‘heat dome’ to its glossary back in 2022.
In the case of separately defining the two terms, then, ‘heat dome’ is used to describe what’s happening in the atmosphere: the very specific formation of a stationary system of high pressure trapping hot air, continuing to do so until the system lessens or moves on.
Heat waves, on the other hand, can be thought of as a consequence of a heat dome, according to research professor of atmospheric sciences at North Carolina State University Ken Kunkel.
Heat waves can be caused by a plethora of factors, including heat domes, and the emission of greenhouse gases. As a spokesperson for the Weather Forecast Research Team at the University of British Columbia says: ‘Heat domes will always be a heat wave, yet not every heat wave is a heat dome.’
However, some experts prefer to iron out any confusion and forgo the term ‘heat dome’ entirely – instead using ‘heat wave’ to describe all weather patterns of extended periods of high temperatures. For British Columbia-based Environment Canada meteorologist Armel Castellan, there is no major difference between the two terms, and that they operate on ‘kind of the same mechanism’.
Ultimately, there are conflicting stances within the scientific community on defining ‘heat dome’ versus ‘heat wave’, but one thing is certain: either way, the planet is getting warmer.
Are heat domes getting worse?
It’s well-understood that heat waves are becoming more severe in both frequency and intensity in recent decades, due to the impact of greenhouse gas emissions on the planet. In the 1960s, around two heatwaves occurred in major US cities per year. In the 2010s, that figure rose to an average of six.
As for heat domes, it is certain that they are becoming warmer due to climate change. Several studies support this fact; one conducted during a 2021 heat dome in Canada found that extreme temperatures were ‘virtually impossible without human-caused climate change’.
Attributing an increase in frequency of heat domes due to climate change, however, is less well understood. Studies continue to evaluate how rising planetary temperatures will affect the mechanisms that cause the weather phenomena, although one noted there would be ‘an increase in summer heat-dome-like stationary waves’ across the US Northwest.
In the UK, the Met Office has warned that Britain’s climate is rapidly changing, with records constantly being smashed and extreme heat and rainfall quickly becoming normal. In addition to this, the nation has also seen wildfires near Wimborne in Dorset and at Edinburgh’s Arthur’s Seat in the last few days.
