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Heat waves are becoming larger, longer and more widespread, creating a climate threat that researchers and data journalists say is difficult to capture with traditional descriptions of extreme weather.
A major Reuters investigation has introduced the term “heat storm” to describe exceptionally large heat-wave events that, at their peak, cover at least 1% of the Earth's surface—an area roughly half the size of Canada.
The investigation analyzed hourly global temperature data dating back to 1960 and consulted two dozen climate researchers and scientists. Reuters found that extreme heat events once regarded as relatively isolated regional episodes are increasingly occurring across enormous areas and for prolonged periods.
The investigation comes as independent scientific research also finds that heat stress is intensifying globally, with dangerous “feels-like” temperatures becoming more frequent, severe and persistent across every continent.
What Is a “Heat Storm”?
The term “heat storm” is not currently an internationally recognized meteorological classification equivalent to a hurricane or tropical cyclone.
Instead, it is a new framework developed by Reuters journalists Maurice Tamman and Ben Welsh to describe the largest and most geographically extensive heat waves identified through their analysis.
Reuters defines a heat storm as a heat wave that covers at least 1% of the planet at its peak.
That threshold is significant because 1% of Earth's surface represents an enormous geographical area. Reuters compares it to roughly half the size of Canada.
The journalists argue that traditional descriptions such as “heat wave” can make exceptionally large events sound like localized weather episodes when, in reality, the same extreme-heat pattern can affect multiple countries and continents simultaneously.
The comparison is similar to the difference between a tropical storm and a hurricane: the underlying phenomenon is related, but the scale and consequences can be dramatically different.
A Record Heat Event Across Six Continents
One of the most striking findings in the Reuters investigation was the existence of a record-setting heat storm that affected communities across six continents.
The effects were dramatically different depending on location.
In the Philippines, students reportedly collapsed in classrooms struggling with extreme heat. In the Amazon, unusually high temperatures contributed to mass deaths among iconic pink river dolphins. In Texas, high school football players faced dangerous heat conditions and some required hospitalization.
These events might ordinarily be reported as separate local stories.
Reuters' investigation argues that looking at them collectively reveals a larger pattern: extreme heat is increasingly becoming a global phenomenon rather than a series of unrelated regional emergencies.
Heat Does Not Always Produce Dramatic Images
One of the major challenges of communicating extreme heat is that it does not necessarily produce the dramatic images associated with hurricanes, floods, wildfires or earthquakes.
A hurricane can destroy buildings and leave visible debris. A wildfire can produce enormous flames and smoke. A flood can transform streets into rivers.
Extreme heat is often less visible. People may collapse indoors, workers may become ill at construction sites, crops may fail, animals may die and electricity systems may come under pressure without producing one dramatic image that captures the entire disaster.
Reuters journalists said researchers studying climate communication told them that giving extreme heat recognizable boundaries and terminology can make the danger easier for the public to understand.
This is one of the reasons the investigation attempts to define, map and name major heat storms.
Scientists Are Also Documenting a Major Increase in Heat Stress
The Reuters investigation is consistent with new peer-reviewed research published in Nature Climate Change in June 2026.
Researchers analyzed global heat stress since 1950 using the Universal Thermal Climate Index, which incorporates temperature, humidity, wind and radiation to provide a measure more closely related to how the human body experiences environmental heat.
The study found a pronounced intensification of heat stress since the 1970s.
Extreme “feels-like” temperatures have become more frequent on every continent, while the geographical footprint of hazardous heat has expanded.
The research also found that the hottest nights are warming faster than the hottest days. Since the 1970s, the hottest nighttime temperatures have increased at an average rate of approximately 0.32°C per decade, compared with approximately 0.27°C per decade for the hottest daytime temperatures.
That nighttime trend is particularly important for human health because people need cooler nighttime conditions to recover from daytime heat.
When temperatures remain unusually high overnight, the body has less opportunity to cool down.
Dangerous Heat Is Becoming More Widespread
The scientific evidence indicates that the problem is not simply that the hottest places on Earth are becoming hotter.
The geographical footprint of dangerous heat stress is expanding into places that historically experienced less extreme conditions.
The Nature Climate Change study found that heat-stress days and tropical nights have increased and that some regions are experiencing up to 50 additional heat-stress days each year.
This creates a challenge for communities that may have limited experience with extreme heat.
Buildings may not be designed for prolonged hot conditions. Hospitals and emergency services may face sudden increases in demand. Workers may have limited protection. Schools may lack adequate cooling systems.
Cities can be especially vulnerable because concrete, asphalt and other urban surfaces absorb and retain heat.
Heat Is a Major Public Health Threat
The health consequences of extreme heat extend well beyond discomfort. The World Health Organization describes heat as an important environmental and occupational health hazard. Heat stress can worsen cardiovascular disease, diabetes, respiratory illnesses and mental-health conditions and can increase the risk of accidents. Severe heatstroke can become a medical emergency.
The WHO estimates that approximately 489,000 heat-related deaths occurred annually between 2000 and 2019, based on available studies.
Older adults are particularly vulnerable. According to the WHO, heat-related mortality among people older than 65 increased by approximately 85% between 2000–2004 and 2017–2021.
These numbers demonstrate why extreme heat is not simply a weather inconvenience. It is a major public-health issue.
Humidity Makes Extreme Heat More Dangerous
Temperature alone does not determine how dangerous an environment becomes. Humidity is also important because the human body relies heavily on sweating and evaporation to remove heat.
When the air contains large amounts of moisture, sweat evaporates less efficiently. This can make it harder for the body to regulate its temperature.
Climate Central reported in June 2026 that dangerous humid-heat days had more than doubled globally since the 1970s, primarily because of human-caused climate change.
The organization defines dangerous humid heat in its analysis using a daily maximum wet-bulb temperature of at least 25°C.
The increase means that some communities are increasingly exposed not only to hotter temperatures but to combinations of heat and humidity that make those temperatures more difficult for the human body to tolerate.
The Problem Extends Beyond Summer
Extreme heat is often viewed as a seasonal problem, particularly in countries accustomed to hot summers.
Reuters' investigation argues that this perspective can obscure the broader trend.
The largest heat storms can persist for long periods and occur over enormous areas. Their effects can therefore extend beyond a single hot day or even a conventional summer heat wave.
The Nature Climate Change research similarly found that the heat-stress season has lengthened in the Northern Hemisphere. This means communities may have to prepare for heat risks over longer periods of the year.
Agriculture and Ecosystems Are Also at Risk
Humans are not the only victims of extreme heat.
Plants and animals can be affected when temperatures remain outside their normal ranges. Reuters documented impacts including the deaths of Amazonian pink river dolphins during an extreme heat event.
Marine ecosystems are also vulnerable to prolonged periods of unusually high temperatures. Extreme heat can alter water temperatures, damage habitats, reduce oxygen availability and disrupt food chains.
On land, prolonged heat and drought can reduce crop yields and increase water demand. This means that heat storms can become economic events as well as environmental and health emergencies.
Infrastructure Faces Growing Pressure
Extreme heat also places enormous stress on infrastructure.
Electricity demand can rise as households and businesses increase air-conditioning use.
Roads and railways can be damaged by excessive temperatures. Power systems can become vulnerable when demand reaches unusually high levels.
Buildings designed for historical climate conditions may become increasingly inadequate as temperature extremes change.
For developing countries and communities with limited resources, adaptation can be particularly difficult.
The risks are therefore not distributed equally.
The Most Vulnerable People Face the Greatest Risk
Heat does not affect every person in the same way.
Older adults, young children, people with certain medical conditions, outdoor workers and people living in poorly ventilated or inadequately cooled housing can face greater risks.
People working outdoors may have little ability to escape dangerous temperatures during the hottest part of the day.
Low-income households may also have fewer options for air conditioning, cooling centres or other forms of protection.
The World Health Organization identifies heat as both a health and occupational hazard and emphasizes the need for heat-health action plans and early-warning systems.
Why Naming Heat Storms Could Matter
Hurricanes receive names because naming helps governments, journalists and the public identify individual events and communicate their risks.
Reuters argues that a similar approach could make major heat events easier to understand.
Instead of describing an extreme temperature episode as another heat wave, a named heat storm could be tracked from its development to its peak and eventual decline.
Researchers could then study how often such events occur, how large they become, how long they last and what damage they cause.
Reuters' methodology was developed with input from climate scientists, including researchers working on marine heat waves, historical temperature ranges and climate data.
The approach is intended as a communication and measurement framework rather than a replacement for existing meteorological warning systems.
A New Way of Understanding Climate Change
Global warming can be difficult for individuals to visualize.
A change in the planet's average temperature by a fraction of a degree does not necessarily feel dramatic on an ordinary day.
Extreme heat provides a much more direct connection between climate science and daily life.
People experience the temperature outside their homes, workplaces and schools. Farmers experience heat through crop conditions. Hospitals see the health consequences. Cities experience increased energy demand.
Reuters' investigation argues that large-scale heat storms can therefore provide a tangible way of understanding what a warming climate means in everyday life.
What Governments Can Do
The growing risk of extreme heat means governments need to prepare for both immediate emergencies and long-term climate change.
Heat-health warning systems can provide advance notice to communities.
Cities can expand tree cover, shade and cooling infrastructure. Building standards can be adapted for hotter conditions. Employers can modify working hours and provide adequate hydration and rest for outdoor workers.
Hospitals and emergency services can prepare for heat-related surges in demand.
The Nature Climate Change researchers specifically identify heat-health action plans, early-warning systems and urban cooling measures as important adaptation strategies.
At the same time, reducing greenhouse-gas emissions remains essential because adaptation alone cannot eliminate the underlying driver of long-term warming.
Canada Is Not Outside the Risk
Although many of the examples in the Reuters investigation come from warmer parts of the world, Canada is also experiencing increasing exposure to extreme heat.
Canadian communities have experienced increasingly serious heat events in recent years, demonstrating that northern countries are not immune to the consequences of a warming climate.
The expansion of heat stress into regions that historically experienced fewer dangerous heat conditions is particularly important for Canada.
Canadian cities, health systems, schools, workplaces and long-term-care facilities must increasingly consider heat preparedness alongside other climate risks.
A Warning for the Future
Reuters' investigation does not suggest that every heat wave should automatically be classified as a heat storm.
Instead, it draws attention to a new scale of extreme heat—events so large that they cross national and continental boundaries and affect billions of people through interconnected environmental, health and economic consequences.
The scientific evidence supports the broader warning.
Global heat stress is becoming more frequent, more intense and longer-lasting, while dangerous heat is reaching a growing share of the world's population.
The challenge now is not only to measure these events but to prepare societies for them.
The Meaning of Heat Storms for the Coming Decades
The emergence of the term “heat storm” reflects a broader change in the way scientists, governments and the public may need to think about extreme heat.
For decades, heat waves were often treated as short-lived regional weather events.
The latest research and Reuters' global analysis suggest that some extreme-heat events are operating on an entirely different scale.
They can cover enormous areas, persist for prolonged periods, affect multiple continents and create simultaneous risks to human health, ecosystems, agriculture and infrastructure.
Naming and tracking these events will not stop global warming.
But a clearer understanding of their scale could make the danger easier to communicate—and could help governments design better warning systems, emergency plans and long-term climate adaptation policies.
As Reuters' investigation demonstrates, the most dangerous climate events may not always be the ones that produce the most dramatic images.
Sometimes the warning is visible in temperature data, hospital admissions, struggling ecosystems and communities that simply cannot cool down.
Sources: Reuters Special Report on Heat Storms; Nature Climate Change; World Health Organization; Climate Central.