“Bull!” said Kerry Emanuel, an atmospheric scientist at MIT.

Jim Anderson of Harvard University was showing him some weird data he had collected. Since 2001, Anderson and his team had been studying powerful thunderstorms by packing instruments into repurposed spy planes and B-57 bombers, among the only planes capable of flying into the storms “without having their wings ripped off,” Anderson said. To his puzzlement, the instruments detected surprisingly high concentrations of water molecules in the stratosphere, the usually drier-than-dust uppermost layer of the atmosphere. They found the water over thunderstorms above Florida, and they found it over thunderstorms in Oklahoma—water as out of place as a dolphin in the Sahara.

While water in the stratosphere might seem innocuous, the finding made Anderson “profoundly worried,” he recalls. From the decades he had spent studying the depletion of the earth’s ozone layer—the thin gauze of molecules in the stratosphere that blocks most incoming ultraviolet radiation—Anderson knew that water could, through a series of chemical reactions, destroy ozone.

It was when he told Emanuel that violent thunderstorms seemed to be heaving water high into the atmosphere that his MIT colleague expressed his skepticism. A quick back-of-the-envelope calculation showed “you’d need an updraft of 100 miles an hour” to do that, Emanuel said. Impossible.

Anderson persisted, and by early 2012 he had demonstrated the connection. Scrutinizing data from the high-altitude flights, he showed that summer thunderstorms were indeed injecting water molecules into the stratosphere. There, sulfate aerosols (from industrial pollutants as well as volcanoes) attract the water molecules like a sponge and, plumped up, provide a bed for chemical reactions that destroy ozone. The destruction can persist for days or weeks. Oh, and one more thing: The violent storms that inject water vapor into the strato­sphere might be getting more powerful and more frequent under the influence of global warming.

Anderson had made a revolutionary connection between climate change and ozone loss. For three decades, scientists have shouted themselves hoarse insisting the two planetary threats were separate and unrelated. “What Anderson did is piece together all of the complicated parts—how you can inject water in higher and higher amounts into the upper atmosphere and how that causes ozone destruction—and come up with this alarming possibility,” says atmospheric scientist Ralph Cicerone, president of the National Academy of Sciences, who has done pioneering work on the ozone layer. “He’s identified a really important mechanism.”

And if Anderson is right and the ozone layer is under renewed attack, then all of the potential consequences of that threat are back like a bad dream from the 1980s: more ultraviolet light reaching the ground; more cases of skin cancer and cataracts; damage to plankton and other organisms that support ocean life; and withered crops that could lead to skyrocketing food prices.

***

Anderson, courtly and white-haired at 68, is writing in longhand at his desk in Harvard’s Mallinckrodt Laboratory early on a sunny autumn morning. The surrounding offices are still dark and empty; Anderson has been at it for over an hour, he says.

But scholarly research isn’t his only passion. He’s also shown unusual devotion to teaching undergrads, lacing an introductory physical sciences class with pragmatic case studies, such as having students calculate their personal energy use. “When I started, I was teaching freshman chemistry the old way, where the idea was to flunk 90 percent of the students,” says Anderson. “But that wastes a huge amount of creative talent and drives students away from science, never to return.”