A new Reuters investigation has introduced the term “heat storm” to describe supersized heat waves that can cover vast portions of the planet for months or even years. The analysis found that these events have surged from about five a year in the 1960s to roughly 102 a year this decade, reshaping how scientists and the public understand extreme heat.
What Is a Heat Storm?
Reuters defines a heat wave as five or more consecutive days of abnormally high temperatures, using the hottest 10% of historical temperatures for each location. A heat storm is a heat wave that, at its peak, covers at least 1% of Earth’s surface—roughly half the size of Canada.
The term is a new analytical concept developed by Reuters, not an official meteorological classification. It is designed to capture the scale and duration of modern heat events that no longer fit the traditional idea of a local heatwave.
Heat Storms Have Risen Sharply Since the 1960s
Reuters analysed hourly global temperature data from 1960 onward across more than one million grid squares, consulting over two dozen climate researchers and meteorologists.
The findings show:
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Heat storms averaged about five a year in the 1960s.
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This decade, they average around 102 a year.
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The average area of the planet covered by heat waves and heat storms has increased more than twelvefold.
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Carbon dioxide levels have risen by more than 30% over the same period.
The analysis links the rise in heat storms closely to rising greenhouse gas emissions, with El Niño acting as an additional accelerant.
Heat Storm Vera: The Largest on Record
The largest heat storm identified by Reuters is Heat Storm Vera, which lasted 367 days across 2023 and 2024. At its peak, it covered nearly 85% of the planet, touching virtually every human being on Earth.
Vera was linked to a series of major disasters:
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Deadly heat during the Hajj pilgrimage in Saudi Arabia, where temperatures at Mecca’s Grand Mosque reached 51.8°C and more than 1,300 pilgrims died.
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Intensified wildfires and drought in Louisiana, contributing to a historic fire season and a deadly highway pile-up caused by “super fog.”
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A Mediterranean cyclone that helped drive catastrophic flooding in Libya, where two dams burst near Derna.
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Extreme heat in the Philippines, where schools were forced to suspend in-person classes as students collapsed in dangerously hot classrooms.
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Severe drought and crop failures in Spain and West Africa, contributing to soaring olive oil and cocoa prices.
Reuters says Vera affected nearly 85% of the planet over its lifetime, making it the largest heat storm on record.
Heat Storm Cascades: 18 Years of Continuous Extreme Heat
Reuters also identified a pattern of heat storm cascades, where large heat events overlap, merge and split off from one another.
The analysis found that a cascade began on July 6, 2008 and has continued without interruption for more than 18 years, or 6,681 days. During that period, at least one heat storm has been active somewhere on the planet at all times.
The ongoing cascade has included 56 mega heat storms, defined as those reaching more than a tenth of the planet’s surface. Before the cascade began, only five such events had been recorded in the previous half-century.
Heat Storms Are Reshaping Global Weather and Disasters
Heat storms are not just isolated weather events. Reuters says they are increasingly connected to wider systems of drought, wildfire, flooding and crop failure.
Examples include:
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Europe’s largest recorded fire in Greece, which occurred during Vera.
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The collapse of a Nepalese glacier in 2026, preceded by weeks of extreme heat.
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Record June temperatures in Bordeaux, Budapest and Bilbao during a 2026 heat storm that contributed to more than 10,000 excess deaths in a single week in Europe.
The analysis also found that heat storms now account for nearly 43% of the planet’s unusually hot days, up from about 3% in the 1960s.
Why the Term ‘Heat Storm’ Matters
Reuters says the term is meant to make the scale of modern extreme heat easier for the public to understand. Unlike hurricanes or typhoons, heat storms have historically not been named or tracked as single, coherent events.
The company has launched an online Heat Storm Tracker as part of its weather coverage, allowing people to see where heat storms are active and how they connect to broader climate impacts.
Researchers say the concept could help communicate the growing threat of extreme heat, which is already linked to hundreds of thousands of deaths each year and is expected to worsen as global temperatures continue to rise.
