Scientists Discover "Heat Storms" Blanketing the Planet

Two Reuters data journalists set out to answer a simple question: What exactly is a heat wave? What they found was far bigger than they expected. After studying decades of climate data, Maurice Tamman and Ben Welsh discovered a new kind of extreme heat event — one so massive and so constant that they had to invent a new name for it. They called it a 'heat storm,' and their findings are changing the way scientists and the public think about our warming planet.

Tamman and Welsh started by digging through climate records going all the way back to the 1960s. They quickly ran into a problem: there is no single, agreed-upon definition of a heat wave. Different countries and weather agencies use different rules for what counts as one. So the reporters talked to dozens of climate scientists around the world and came up with their own clear definition. They decided a heat wave is any stretch of five or more days where temperatures rank in the hottest ten percent for that location.

Once they had that definition, they needed to set a bar for something even bigger. A heat storm, they decided, is a heat wave that grows large enough to cover at least one percent of Earth's surface at its peak. That might not sound like much, but one percent of Earth's surface is roughly half the size of Canada. When they mapped these events over 80 years of data, the results stunned them.

In the 1960s, there were about five heat storms active on the planet at any given time. In the 2020s, that number has jumped to 102. Even more surprising, since July 6, 2023, there has not been a single day without at least one heat storm active somewhere on Earth. 'There are people who are going to go to the polls in the U.S. this November who have never lived on the planet at a time when there wasn't at least one heat storm active,' Tamman said. He called that fact 'utterly staggering.'

Heat storms are not just more common — they are also much bigger and longer-lasting. The largest heat storm recorded in the 1960s covered about six percent of Earth's surface during its entire lifetime. By contrast, a recent heat storm the reporters named 'Vera' lasted one year and one day, and during that time it touched 85 percent of Earth's surface. That means almost every person alive on the planet felt its effects at least once.

The team gave names to heat storms for an important reason. Naming a storm makes it feel like a real, defined thing with a shape, a size, and a lifespan — much like hurricanes are named. 'If we can't name it, how can we talk about it at all?' Welsh said. Giving Vera a name made it easier for readers to follow the storm's path and understand its impact on people in different places.

The reporters traveled around the world to show what Vera did to real communities. In Texas, a high school football player suffered dangerous heat illness during a Friday night game and ended up in the hospital. In the Amazon rainforest, hundreds of pink river dolphins died because the water in their lake became too hot for them to survive. What happened to both the football player and the dolphins shows how heat storms can harm living things far apart from each other.

The scale of heat storms also surprised Welsh when he saw it on a map. He realized that the extreme heat hitting Europe one summer was part of the same massive storm that caused a glacier on the Nepal-China border to collapse, flooding entire towns. What looked like separate events on the news were actually one connected heat storm stretching across the globe.

Tamman said the goal of the project was always to connect the science of climate change to everyday life. People feel hot on a summer morning and complain about the temperature, but they rarely connect that feeling to the larger changes happening in Earth's climate. Heat storms, Tamman believes, are a powerful way to make that connection clear. 'We were looking for a way to communicate how global warming is connected to daily lives,' he said.

Welsh and Tamman say this is only the beginning of their reporting. Future stories in the series will look at the health effects of heat storms, how they are connected to deaths, and how they affect plants, animals, and natural disasters. 'The numbers are just the beginning of the story,' Welsh said. 'Our job is to turn numbers into news.' Both journalists hope their work helps the public better understand — and respond to — one of the biggest challenges facing the planet.