The Science of Making Rain (2024)

For as long as humans have been around, we’ve been at the mercy of the weather. And as long as that’s been the case, we’ve wanted a way out—a way to control the weather to suit our needs. In the distant past, we used sacrifices and rain dances. Today, we turn to science.

This is where cloud seeding comes in. It’s humanity’s attempt to do what has always seemed impossible: To harness the clouds and make them rain.

LISTEN: “The Science of Making Rain”

Let’s begin in Fargo, North Dakota, at the headquarters of Weather Modification Incorporated, WMI. It’s the largest cloud-seeding company in the world.

“I like to say we’re the Microsoft or the Starbucks of the weather modification world, because we’ve got like 14 full-time personnel,” Hans Ahlness says, laughing. Ahlness is the vice president of operations and he guides us through the Bravo Hanger. It’s a white warehouse about the size of a football field.

“So here’s another kind of airplane. This is a piston-twin. This one’ll be in California this winter, making snow.”

WMI uses these airplanes to seeds clouds for water districts, public utilities, hydroelectric power companies—any organization that wants more precipitation.

“What they’re trying to do is make more snow that, in the spring, melts and then fills dams for hydroelectric power. In California, water gets used about three times. So it’ll be hydroelectric power, it’ll be irrigation, municipal water. Maybe eventually it’ll get to the ocean,” he says, laughing.

In a couple weeks, WMI will send its fleet of planes to Wyoming, Idaho, Nevada and California. Once they get there, they’ll fly into frigid winter clouds, spraying a mist of chemicals, hoping to trigger snow. And when it gets warmer, they’ll fly somewhere else and make rain instead. We’ll get to how cloud seeding works in a little bit. First, some history.

Over the years, people have tried all kinds of crazy ideas to squeeze more water out of the sky. Jim Fleming is a professor of science, technology and society at Colby College, and he says one of the first big rainmaking projects in America was proposed in the 1830s by a meteorologist named James Espy. Espy thought he could increase precipitation by sending hot air into the atmosphere, which would then cool and fall as rain. His big idea was to set fire to the Appalachian Mountains every weekend.

“And by Monday morning, the air would be fresh and the rivers would be full and recharged with water and the fields would be watered as well. People thought he was really crazy,” Fleming says.

But Espy was completely sane compared to General Robert Dyrenforth, who got into the rainmaking game in the 1890s. (He wasn’t a real general by the way—he just called himself one.) Dyrenforth thought that explosions shook the clouds and caused rain. And so, with federal funding, he put together a huge arsenal of explosives and headed to Texas.

“And he proceeded to try to make it rain by shooting off fireworks, by floating balloons that were filled with hydrogen and blowing them up in the sky,”

Fleming says it was very entertaining for the locals. But it didn’t work—at all.

Now, fast-forward about half a century to 1947. That year, three scientists at the General Electric Corporation’s research lab were working on making artificial clouds: Irving Langmuir, Vincent Schaefer and Bernard Vonnegut. (A fun aside: Yes, Bernard was Kurt Vonnegut’s brother. And some of Kurt’s sci-fi novels were inspired by Bernie’s work.)

“These three—Langmuir, Schaefer and Vonnegut—are kind of known as the triumvirate of the early days of cloud seeding,” Fleming says.

One day, the triumvirate was working in the lab, making little clouds in a freezer box. Schaefer took some dry ice—the same stuff people use to make fog in a haunted house—and scraped it into a cloud they just made. And it blossomed into millions of tiny ice particles—aka, snow.

“And he says, ‘Aha—I think I’ve got something here.’ And so he went out with a rented airplane over the Berkshires and they sprinkled some dry ice over a cloud and they made a little snowstorm.”

Here’s why it worked:

Clouds are full of water, but they won’t precipitate unless there’s an impurity in the cloud—some little fleck for the water molecules to glom onto, like soot or mineral dust. In this case, it was the dry ice. Once that impurity enters the picture, it becomes the nucleus of an ice crystal, and that crystal attracts water molecules and gets heavier and heavier—until it falls as snow or hail, or melts into rain on the way down to earth.

And while Schaefer seeded that first cloud over the Berkshires, Irving Langmuir, the lead researcher on the team, watched from the airport below.

“And immediately he was on the phone to theNew York Times before the plane even landed with a storyline that man can control the weather,” Fleming says.

The very same year, Bernard Vonnegut discovered a chemical that worked even better than dry ice. It’s called silver iodide, and it mimics the structure of a natural ice crystal, so it’s the perfect particle to attract water molecules and jumpstart precipitation. In fact, most cloud seeding operations today still use silver iodide.

Back in Fargo, WMI seeds clouds all over the world—from India to Canada to Saudi Arabia. They get lots of business. But there are also plenty of critics. And they fall into three camps. First, there’s the folks who worry about the environmental repercussions. And it’s true, pumping clouds full of silver iodide sounds scary. But so far, studies haven’t found a negative effect on the environment.

“I mean you could eat it on your Wheaties except it tastes horrible, so I wouldn’t recommend it,” says WMI’s Hans Ahlness.

And yes, he’s tasted it.

“Sure, I mean, just mixing chemicals and stuff—you get it on your hands and you get a little mouthful of it.”

Conspiracy theorists make up the second group of detractors. These are people who think cloud seeding is part of a worldwide government plot—like chemtrails or fluoride in the water. Ahlness gets a lot of angry phone calls.

“They think we have some sort of godlike powers, where we can move clouds around at will or make a drought, [depending on] whatever fickle mood we’re in that day.”

A while back he had to notify the police when someone called the office over and over again, threatening his employees by name.

The third group is scientists. There’s a lot of doubt among some scientists about how effective cloud seeding even is.

“No cloud is the same as another cloud and no cloud will ever be the same as another cloud,” says Roelof Bruintjes, who studies cloud seeding at the National Center for Atmospheric Research. He says every cloud is a unique and chaotic swirl of variables, so it’s hard to prove that a seeded cloud wouldn’t have rained or snowed anyway if it had just been left alone. And it’s pretty much impossible to replicate results.

“They think we have some sort of godlike powers, where we can move clouds around at will or make a drought, [depending on] whatever fickle mood we’re in that day.”

But thanks to improved technology like satellites and computer models, Bruintjes says their understanding of cloud seeding has increased tremendously over the past 20 years.

The state of Wyoming recently finished a nine-year study on cloud seeding in the mountains. And the data suggest that seeded clouds snow up to 15 percent more than unseeded clouds. But the conditions have to be perfect—the right wind direction, the right amount of moisture, the right temperature.

“So there’s no one experiment you can do in one area that will be transferrable to other areas all around the world,” Bruintjes says.

The bottom line is, cloud seeding seems to work in some conditions, but it’s not an exact science. But it’s also worth pointing out that farmers and water managers and municipalities don’t need an exact science. They need water.

“They say if it works half the time or maybe 10 percent of the time, it is still worthwhile,” Bruintjes says. “Water problems globally are going to increase in the next several decades, and many people will live under severe water stresses. So we are looking at all the tools to enhance the supplies and to sustain the supplies that we have.”

Bruintjes says cloud seeding is not the answer to water scarcity. It’s more like a long-term strategy to shore up local water supplies just a little bit. Hans Ahlness from WMI agrees.

“It’s just another tool to try and improve our lot in life and do it in an environmentally responsible manner,” Ahlness says.

And even though we’ve come a long way since Espy and Dyrenforth, we’re still at the mercy of the weather. You have to work with what nature gives you. We can’t make clouds out of thin air, or orchestrate rainfall, or engineer our way out of a drought. Any real, lasting solution to water scarcity has to start with conservation—with major changes in the way we use water in industry and agriculture and daily life.

It’s a tall order. But hey, if we can make it rain, we can do anything—right?

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This story is a production of the STEM Story Project, which is distributed by PRX and made possible with funds from the Alfred P. Sloan Foundation.