Most people have already lived through heat waves, as they are becoming more frequent and stronger due to global warming. But when our colleagues Maurice Tamman and Ben Welsh started analyzing larger sets of data around heat waves, they realized that a new category is needed: “Heat storms” conveys the scale and consequences of the largest heat waves that, at their peak, cover at least 1% of the planet – about half the size of Canada.

Today’s newsletter highlights Reuters' Heat Storms series, a data-driven investigation into how extreme heat is reshaping lives, infrastructure and economies around the world.

Scroll down to read an interview with Maurice and Ben on what their analysis found, what went into the reporting process, and how to make an invisible crisis, like heat storms, visible.

We also want to hear from our readers to show how far the effects of heat storms have reached around the world. How have extreme weather events shaped your year? Share your experience with our journalists in this form.

And if you are working directly or indirectly on environmental policy or disaster mitigation, we would love to hear from you on what your government or institution is working on to mitigate weather phenomena like heat storms. Write to us at sustainableswitch@thomsonreuters.com or hit reply to this Defining danger Q: Your project follows one record-breaking heat storm across six continents. What surprised you most about the common threads connecting communities thousands of miles apart?

A: Tamman: From the first moment I started animating the storms over time, I could see this one thing unifying disparate, otherwise unconnected parts of the world: these heat storms. I didn't even have a name for them at first; I just knew they were not heat waves in the parochial sense. They were so much bigger than heat waves as I’d considered before. And as the first story shows, every corner of the world is struggling to cope with these massive temperature events, whether it's Filipino students fainting by the dozens in classrooms cooled only by fans, the Amazon’s iconic pink dolphins dying in droves, or Texas high school football players struggling under Friday Night Lights and getting hospitalized. Before now, no framework connected those events. Now there is.

Q: Is "heat storm" simply a more powerful way of communicating heat waves, or does it fundamentally change how we measure and understand risk?A: Welsh: As data journalists, our job is to turn numbers into news. We’re always looking for ways to measure things. When I started on this project, I expected to find an easy-to-calculate formula for a heat wave, much like how a hurricane is defined as winds over 74 mph. It turns out, no globally recognized definition exists. So we made one of our own.

Tamman: A heat storm differs from a heat wave much like a hurricane differs from a tropical storm. Heat storms are heat waves on a vast scale, and defining them differently helps the public understand how this new, bigger phenomenon, which has enveloped the planet in recent decades, puts billions of people at risk and damages ecosystems every day.

We also name heat storms, as we do with hurricanes, so people can easily track them and start tallying their damage. Defining the danger is the first step toward understanding risk.

Q: One of the challenges of covering extreme heat is that it often lacks the dramatic imagery of other disasters. How did you make an invisible threat visible?

A: Tamman: Some researchers and scientists who study the communication of climate change and global warming told me it is easier to explain and document risk when the event is “objectified” with recognizable boundaries and a clear definition. Despite the hundreds of thousands of people who die every year from the heat, it can be an amorphous threat.

The imagery was always there, but you can’t connect events to larger forces without a framework for understanding them. Consider the August glacial collapse in Nepal that killed thousands. Some stories immediately following the disaster said climate change contributed to its (glacier's) demise. But again, that is so amorphous. Saying that hundreds of days of heat waves and heat storms blanketed the region in the years and months before it failed is a simple, concrete concept anyone can grasp (and is harder to dismiss). It explains how global warming contributed to the deaths of thousands of people.

Welsh: While it’s nowhere near as visceral as the events in Nepal, data visualization also plays an important role here. The impact of climate change is slow-moving, complex and global. It’s far bigger than any of us can understand on our own. One way to better understand the big picture is to study data that tracks changes in our world. That’s why we launched the Reuters Climate Monitor, which compares today's weather forecast against the historic record, mapping out temperature extremes as they occur.

Q: If heat storms become as familiar a term as hurricanes or atmospheric rivers over the next decade, what is the single most important consequence you hope policymakers and the public take away from this reporting?

A: Tamman: Heat waves, even the worst of them, have typically been seen as regional, sporadic issues. What that perspective misses, however, is how much of the globe is under a pall of heat waves and storms. And while the most obvious consequences come during the warmest times of the year, the effects are year-round and feed into the spiralling rise of temperatures every year. What do I hope? I hope that folks read this series. I hope that it shifts the public’s perspective, even incrementally, on how our planet is changing and warming. I hope that defining, mapping and naming heat storms spurs policymakers to recognize and track the damage heat storms are doing.

That said, I am under no illusion that our work will change public policy; if it does, it will be because the public’s perspective has shifted enough for policymakers to listen. Listen, I love warm weather. For most of my life, I have half-joked that life is better served with a sheen of perspiration. But when that comes at the expense of our planet, I would happily settle for a few more cardigan days.

The methodology of heat storms Four of the two dozen researchers and scientists interviewed for this project were particularly influential in developing the methodology. Alistair Hobday, of CSIRO, Australia’s national science agency, for his work on marine heat waves;Lukas Brunner, at the University of Hamburg, who helped with the seasonal adjustments and baseline temperature ranges;Claudio Piani at the American University of Paris, who also helped develop the historical temperature ranges; andEd Hawkins at the University of Reading, who convinced the team that this was not a fool’s errand.

Click here for a detailed description of sources, definitions, and methodology that went into the project.

Track the heat storms Follow the supersized heat waves reshaping our world. Click here to explore the Reuters Heat Storm Tracker, part of the Climate Monitor.

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