Clouds hold the key to forecasting climate change But they’re extremely difficult to understand, let alone measure Meet the storm chasers who try to do it anyway THUNDERHEADS

Flying low along a mountain ridge in central Argentina, Clayton Eveland slaloms right and left, steering the plane through one cloud after another, each one turning the cockpit windshield briefly white. Reaching the end of the range, he wheels around and takes a lower pass, the plane’s sensors sampling the air between the clouds and their shadows on the patchwork farmland below. A former bush pilot now working for the Department of Energy, Eveland has flown through just about every type of cloud the planet has to offer: sprawling stratus decks above the Alaskan tundra, atmospheric rivers flowing toward the coast of California, low ocean haze in the Azores, and orange pyrocumulus plumes sent up by firestorms in Washington state (which he describes as a “hoot”). Eveland likens skimming along the Argentine mountains to surfing, though every time he says something like that, he’s quick to boast about his caution. “This isn’t like Twister. We don’t just drive around looking for bad stuff to happen,” he says in his Arkansan twang. “Our sensors have sensors.” Laughing, he gestures to a plastic hula girl suctioned to the cockpit dashboard. “And when she falls off, it’s time to go home.” Eveland is part of a team of about 60 people who have come to Argentina’s Córdoba province to chase the clouds. In the back of the plane are four scientists who enjoy the flights somewhat less than Eveland does; staring at instrument displays as the plane pitches and rolls, someone always throws up. On the ground, other researchers are readying weather balloons and preparing heavy blue trucks mounted with radar dishes. If all goes according to plan, later today, they will capture a high-fidelity picture of the birth, life, and death of a cloud. Not only are clouds complex, but there isn’t much data on them

Climate change has made gathering such data an urgent matter. Clouds play a profound role in the climate system: some types block sunlight, cooling the Earth, while others act as greenhouse gasses and heat it. Yet no one knows exactly how the clouds will behave as the climate warms. Ever since scientists started running climate models in the late 1960s, clouds have remained the largest single source of uncertainty about just how hot the Earth will get in response to carbon dioxide. They are a major part of the reason why scientists give predictions about the future climate as a range: about 3 to 8 degrees Fahrenheit if carbon dioxide concentrations rise to twice their preindustrial levels, which is a point we are on track to reach by mid-century. It’s a margin of error that runs from bad to catastrophic — the difference between billions more people subjected to deadly heat, between damaged coral reefs and the end of them, between the inundation of not just Miami but of Osaka, Shanghai, Kolkata as well. There are signs that clouds hide even more dangerous tripwires. Earlier this year, Tapio Schneider at the California Institute of Technology simulated the sprawling banks of stratocumulus clouds that currently blanket the oceans. When he tripled the level of carbon dioxide, the clouds abruptly disintegrated. Global temperature shot up 14 degrees, reaching a point last seen 55 million years ago, when crocodiles swam in the Arctic. “It was shocking, my God,” Schneider says. “There are unknown unknowns, things that people didn’t think could happen because climate models don’t capture it, but in reality they might happen. We need to get these models better fast.” The cloud problem has remained unsolved in part because clouds are astonishingly complex, made up of trillions of microscopic droplets swirling about chaotically. Modeling even a single one at high resolution requires the fastest supercomputers in the world; modeling a planet’s worth will be beyond our capabilities for decades. We would get the answer too late. Dave Randall, an atmospheric scientist at Colorado State University, calls it an “infinite problem,” like trying to simulate a human being down to the individual cells. It is “the Higgs Boson of the theory of climate, and climate change,” The World Climate Research Programme wrote in a call for cloud research. “It is the intellectual and experimental challenge of our lifetime.” Not only are clouds complex, but there isn’t much data on them. Useful satellite records go back only to the 1970s, and even then, they only provide a view of the cloud tops, not what’s happening beneath them. Gathering the necessary data requires airplanes, balloons, and all manner of radars and lasers, as well as solving a more basic problem: if clouds defy prediction, how do you know where and when to set everything up? The scientists in Argentina have been becalmed for days, waiting for something to happen. As bored people often do, they passed the time by chatting about the weather, periodically gazing out the windows of the hotel where they had set up their headquarters and confirming that the weather was still, regrettably, nice: blue skies, 80s, a bit muggy in the afternoons. Picking over the breakfast buffet, they lamented the layer of hot, dry air that was preventing storms from forming and talked wistfully about a zone of low pressure spinning off the coast of Chile, which the forecaster has given the Godzilla-like moniker “Mega Trough.” Today, it is expected to approach the coast. At the morning briefing, the mission’s forecaster tells the scientists that there is a high likelihood of lightning, hail, and flooding. There are murmurs of excitement across the hotel conference room. As Eveland flies laps through the clouds overhead, the researchers hurry to get ready for the storm.

You created group “RELAMPAGO Ops” RELAMPAGO Ops: ‎Messages to this group are now secured with end-to-end encryption. Steve Nesbitt: Here’s a song for you… Thunderstruck by AC/DC

There are 10 basic types of clouds, according to the International Cloud Atlas, which can be further subdivided into 15 species. Each of the scientists in Argentina has their favorite. Lenticularis, a lens-like cloud formed by air passing over mountains and often mistaken for flying saucers, is a popular one, as are mammatus, the orb-like protrusions that form beneath powerful storm clouds. But the favorite by far is the cumulonimbus, the thunderhead, the tallest and most violent cloud, flinger of hail, shooter of lightning, spawner of tornadoes, and the origin of the phrase “cloud nine,” for the page it filled in an early edition of the Cloud Atlas, and because it can touch the heavens. The thunderhead is what they are here to chase. A cumulonimbus is a convective cloud, forming when hot air rises and the moisture in it condenses onto dust and organic matter floating in the air. Imagine a boiling pot, one of the researchers in Argentina explained. Instead of the burner, you have the sun heating the ground. The rising bubbles are the clouds. The first to appear is the cumulus, the archetypal benign puffball cloud of cartoons. Often, it will simply hang there until it evaporates, but if the air is hot and humid, the cloud will keep bubbling upward to the tropopause, the lid about 10 miles up beneath which most of our weather occurs. The cloud splashes against this limit, forming a cumulonimbus’s characteristic “anvil.” To continue the cooking analogy, it’s now reached a roiling boil. Lightning flashes, and cloud droplets swept aloft by immense updrafts freeze and fuse into hailstones. The process can be as powerful as an atomic bomb. And this sparsely populated stretch of riverside resorts and cattle ranches on the Argentine Pampas has some of the best cumulonimbus in the world. Steve Nesbitt, a professor of atmospheric science at the University of Illinois and one of the co-leaders of the mission, has been eyeing the region since he was in graduate school 20 years ago, when he watched his adviser pore over satellite imagery in search of the most intense storms on Earth. Some confluence of atmospheric currents and geography causes puffy cumulus clouds to form and explode into ferocious storms with unusual frequency. And what storms! Cloud tops that touch the stratosphere, lightning flashing more than a hundred times a second, hail the size of cantaloupes, Nesbitt says.

The hail in particular was notorious for wrecking buildings, cars, and crops. Days before, hail had bashed in the nose cone of a passing airline on its way to Santiago. (When I rented a car to follow the storm chasers, the clerk offered insurance for all manner of destruction except, he emphasized, hail.) A storm in 2015 lasted only 45 minutes, but it was seared into the memory of a local weather watcher: a calm morning, cool air, and then a sudden deluge of ice. “The town was divided in two,” he says. “It was a total disaster. More than 300 cars destroyed. Flooding because hail clogged the street drains and made blocks of ice. The roofs of houses were collapsing under the weight.” Nesbitt, who grew up enraptured by lake effect snow in upstate New York and still has a boyish enthusiasm for extreme weather, knew he had to get here. Like Nesbitt and many others on the mission, Adam Varble, a scientist with the Pacific Northwest National Laboratory and the campaign’s other co-leader, has been entranced by storms from a young age. In his case, it was watching thunderstorms roll across the plains in southeast Wisconsin. But where Nesbitt’s enthusiasm comes off as languidly awestruck, Varble is all meticulous intensity. For him, the appeal of Córdoba’s storms is not their violence, but their dependability — that the spot is a “natural cloud laboratory.”

The challenging thing about clouds is that they are both very large and very small. Clouds cover two-thirds of the planet, but if they all fell to Earth, they would form a puddle no deeper than a human hair. Varble is preoccupied with clouds at the smallest scale, a realm that is paradoxical and poorly understood. Explaining a process as seemingly simple as rain sends him off on spiraling caveats: about the way cloud droplets can remain liquid at temperatures far colder than freezing, how they can suddenly freeze and explode, how their shards interact chaotically with neighboring droplets, and how it all gets very, very complicated. These small-scale processes determine much of cloud behavior, which, in turn, has a profound influence on the climate system.

Exploding Cloud Drops Cloud microphysics are fiendishly complex. Droplets can remain in liquid form at temperatures far below freezing (a state called “supercooled”), only turning to ice when they come into contact with an impurity like dust, salt, bacteria, or ice. When droplets freeze, they can detonate, and their shards can strike other droplets, causing a cascade of freezing called “glaciation.” Whether droplets are liquid or frozen — and if frozen, what shapes they take (plates, pillars, dendrites) — affects what type of cloud forms, whether it rains, and how much sunlight it reflects. Above is a slow-motion video of a supercooled drizzle droplet after it’s touched by a silver iodide pin.

Most models used to predict future climate, however, work by dividing the Earth into grids of 100 kilometers to a side. Capturing small-scale cloud processes would require computers billions of times more powerful than anything available today, so researchers around the world are racing to find other ways to bring down the resolution: nesting fine-grained cloud models inside coarser global ones, simulating clouds with machine learning, and searching for new rules and patterns in cloud behavior. For any approach, more data on clouds is needed, but measuring floating, always-changing clouds presents challenges of its own. The sheer variety of instruments shipped in for the Argentina mission is a testament to its difficulty. There’s the plane, festooned with sensors, its wings hanging with golden prongs, razor-sharp to capture frozen cloud droplets without shattering those nearby. But the plane can only capture a narrow slice of the cloud, Varble says, and it must turn back if hail begins to form. A satellite will target the area during the operation, but it can only see the cloud tops. High on a desolate ridge to the west, the scientists have built a fortress of sensors and shipping containers: a white volleyball radar housing, lasers pointing straight up, an upturned trapezoid emitting digital chirps measuring windspeed, a rifle-like turret tracking the Sun, a thin metal chimney sucking in air and sampling the particles floating in it, a camera that photographs individual falling raindrops, a mirrored dome measuring the portion of the sky covered in clouds. When I visited the site with Varble the day before, it felt like stepping onto a moonbase, all the devices swiveling and chirping, each one measuring a different aspect of the clouds but, Varble lamented, none giving a full picture.

The researchers also have a convoy of mobile radars and other vehicles with which to catch their cloud. They stayed up the night before figuring out a plan, moving their units around satellite maps like pieces on a game board. Along the highway in front of the ridge where models said a storm might form, they placed pickup trucks with mast-like weather sensors on their hoods. Behind them, they stationed three heavy-duty flatbeds with spinning Doppler radar dishes. Other teams will scatter sensors in ditches and fields, completing the net. Finally, three teams armed with weather balloons will take measurements of the air. If a storm forms, the hope is that one will be close enough to chase it and throw a balloon into the cloud itself. Varble will stay in the hotel conference room with a dozen other scientists, watching satellite feeds and helping direct the operation over WhatsApp. Nesbitt, after weeks of managing logistics from the hotel, will take a turn in the field, leading one of the balloon teams. The sky is still blue as the vans, trucks, and radars file out of the field behind the hotel where they had been parked. Their truck loaded up with helium tanks and balloons, Nesbitt and three grad students start driving south. The mood is tense. Any moment could bring an update saying a storm had formed at the wrong place or time and the mission is scrapped, or that they have to race to salvage it. To break the tension, Nesbitt drops a song into the operation’s WhatsApp group: AC/DC’s “Thunderstruck.”

Karen Kosiba: Go for mission today. Sounding lat/lons coming soon. Steve Nesbitt: Roger that Steve Nesbitt: P.S. I’m really excited for today’s mission

Eveland is flying laps along the ridge, diving in and out of the building clouds, which have grown from stray puffs to cotton candy plumes. Weather prediction is cyborg work. Computer models are invaluable, but they must be weighed against other models and trued by people with experience of how they’ve performed. Sensors provide important information about what the atmosphere is doing, but they must be supplemented with simple visual observation, and few clues are as important as clouds. Eveland is self-deprecating about his knowledge of clouds, saying he never knew they went by so many names until he started flying the scientists. But he knows what to look for. “I always thought there were just fluffy, nice clouds and mean, angry clouds,” he jokes. Mean, angry ones look like a fist with knuckles, their crispness a sign of their power. He gives those a wide berth; they mark updrafts that can flip a plane and fling hailstones for 20 miles. The clouds to his south, back by the airport, were looking angry. He’d been watching them grow taller all morning, and now he could see the hazy white splash of a cumulonimbus’s anvil high in the atmosphere. Varble had been watching the storm, too, from the satellite feed on his laptop back at the command center. Fearing the plane would be cut off, he tells Eveland to head for home.

As Eveland speeds back toward the airport, clouds unfurl around him, and the sky takes on a sepia tint. The plane starts bucking even more than usual. He comes in to land, noting the ripples in the fields below indicating that the wind had begun to shift ahead of the storm. He hits the tarmac and makes for the hanger. Hail peppers the runway not long after. But back in the operation zone to the north, the sky is still blue. The researchers have driven their radar trucks into position, anchored them with steel struts, and pointed their dishes at the ridge where they expect a storm will form. Now, there is nothing to do but wait. Nesbitt’s truck is parked in a field along the side of a two-lane highway, in front of a large, unassembled radar that was shipped in the week before. When I drive up, he is lounging in the shade beneath the bed of his truck, watching the clouds through mirrored sunglasses. Insects whir, and the field shimmers with heat. Days of weather simulations have brought the researchers to this point, but cloud droplets are too small to be picked up by radar, and models can’t predict exactly where and when a cloud will form and grow into a storm. From here onward, they will have to rely on their eyes. “The clouds are like fingerprints,” Nesbitt says, pointing to the clouds along the ridge. “You can read them and instantly see what’s happening in the atmosphere.”

To him, the static scene is full of action: clouds “pop” and “bubble,” signs of tremendous energy and continent-scale atmospheric flows. Hot, wet air rising off the ridge is ripe for development into a powerful storm, but it’s being blocked by a layer of warm, dry air aloft. It needs a push. Maybe that will come as the sun continues to beat down and heat the ground, or maybe it will come from the approaching line of innocuous-looking cloud puffs to the south. Those clouds, Nesbitt says, are the result of the storm Eveland had just dodged, now visible as a sprawling white flying saucer in the distance. Its falling rain and hail have cooled the air beneath it, creating what’s called a “cold pool” — that blast of chilled wind that hits you before a storm. The cold pool is sliding north along the ground, pushing hot air up to form that line of clouds, and maybe, Nesbitt says, it will trigger a storm somewhere this afternoon. This is a process not captured by current models, the way one storm can cause others dozens of miles away, so researchers have to fill in the gaps. “Most meteorologists who are any good have this kind of sixth sense about this,” Nesbitt says. The researchers are also aided by locals who, like people everywhere, have their own weather lore. On a farm 50 miles to the south is a 28-year-old farmer’s son named Matías Lenardón who became obsessed with cloud formations and storms after lightning struck his house when he was five. In high school, he grew so frustrated with the lack of local weather data that he built a weather station and recorded its observations for the next 10 years without missing a single day. The radio station in Córdoba now calls on him for morning forecasts before his shift at the granary, and he helped the researchers place their sensors on his family’s farm. Nesbitt says Lenardón reminded him of himself as a kid.

Lenardón uses models and satellite data, but it’s the decade he spent watching the weather that gives him his edge. He knows, for instance, that if the models show a possibility of a storm in the afternoon, fog in the morning and clouds with a greenish tint mean it will be a strong one, and that lately they have been getting stronger, and forming faster, and coming from the mountains in the north rather than the plains to the south, as they used to. People have used clouds this way for millennia, developing rules and rhymes about what they foretell about future weather. Think of “red sky at night, sailor’s delight,” or the dappled cloudlets of a “mackerel sky” signaling rain. It’s not a far leap from there, especially for people whose livelihoods are closely tied to the weather, to seeing in the clouds not just meteorological signs but divine ones. It’s a quality that cuts across history and cultures: clouds acting as the tools of deities from Zeus to Indra, leading the Jews out of Egypt in Exodus, ubiquitous in Christian art as the abode of God and saints. Today, this role is given a secular revision in various conspiracy theories, from weather modification to airplane contrails. (As often happens, the theorists are part right and completely wrong: we are changing the weather, and clouds play a major part, even contrails, which have a significant warming effect.) Varble encounters theories like these wherever he’s working, and he always tries to do lots of community outreach in part to forestall rumors that something nefarious is happening with the US Department of Energy trucks that are parked on remote roads at odd hours, monitoring the clouds. In Colorado, park rangers told him to turn off a laser because it was turning the clouds green and freaking people out. Here in Argentina, as soon as the researchers arrived, they received an email with dozens of photos alleging the region’s strange clouds are the work of aliens. “Nobody’s coming to save us. The Earth isn’t going to save itself. It’s really up to us.” It’s fitting, then, that we’re now looking to the clouds to see what the future holds, and maybe it’s these prophetic associations that make news of their changes so eerie. This summer saw thunderstorms near the North Pole and outbreaks of a rare type of shimmering nighttime cloud over Europe and the United States. Whether these noctilucent clouds have an impact on climate is unclear, but they are linked to increasing emissions of methane, a powerful greenhouse gas, making them a stark reminder that the changes underway extend to the upper atmosphere, and will be as inescapable as the clouds. Other clouds appear to be changing in ways that are subtler but more ominous where climate is concerned. Since the 1980s, they have been migrating toward the poles where they will reflect less sunlight and amplify warming. They also appear to be moving higher in the atmosphere, which will worsen warming, too. The low stratus clouds that drift into California from the Pacific have been growing sparser since the 1970s, likely worsening droughts and wildfires. “Clouds were kind of our last hope,” says Kate Marvel from NASA’s Goddard Institute for Space Studies. They were the only real contender for a protective mechanism that might kick in and dampen the effects of climate change. But the more we learn, the more it looks like they could make things worse. “Nobody’s coming to save us,” Marvel says. “The Earth isn’t going to save itself. It’s really up to us.”

Karen Kosiba: UI2: Please go South on the rio tecero road to rio tecero and await further instructions (please keep collecting data) Russ Schumacher: copy. prepping for launch nbow Russ Schumacher: *now

It is almost three in the afternoon, right around when the models said a storm would form. Conditions seem right for something to happen: the air is getting hotter and more humid, and the cold pool is sliding in from the south. Then the radars pick up a strange signal: a cloud of something flying toward them, too uniform in size to be precipitation. “It has to be biological,” says one of the radar operators. It is, in fact, biological: a swarm of locusts riding the northerly jet out of the Amazon. The enormous insects started appearing several days before, and the bored researchers had taken to measuring them with their hail rulers. They represented another bit of weather lore: locals said their arrival signaled a coming storm. The question was where it would form. In the hotel conference room, Varble notices the clouds above the sensor site on the ridge are rapidly growing thicker. He switches over to the site’s cameras and sees clouds flowing in from the ridgetop, sliding across the blue sky like a stadium roof. At the same time, the satellite shows the line of clouds 50 miles to the southeast, triggered by the airport storm, deepening. Either spot seems ripe for a storm. Karen Kosiba is coordinating the operation. A scientist with the Center for Severe Weather Research, she’d chased tornadoes and ridden out hurricanes atop levees long after everyone else evacuated, and here in Argentina, she’d studied the roads and fields that would now become the redoubts and escape routes for the researchers. There’s a game-like quality to managing a campaign, she says, and now it was time to start putting her pieces in play.

Russ Schumacher, an upbeat atmospheric science professor from Colorado State University, had been waiting in a dusty field, sending weather balloons up every hour. Kosiba tells his crew to head south toward the line of clouds. Their mission is to get a weather balloon into an updraft, the rising hot air that gives storms their power. It’s a difficult task: you have to get under a storm and throw the balloon so that it catches the air currents and gets sucked into the cloud, all without getting hit by hail. Schumacher had boasted earlier that the two graduate students with him were some of the best updraft hunters around. Time to prove it. The three of them hop in their van and drive out of the parched field, dust devils eddying in their wake, toward the road that will take them south. Nesbitt’s mission had been to take balloon readings in the cold pool behind the line of clouds, but he’s taken a break on his way south and is eating ice cream at a gas station in the town of Río Tercero. With Schumacher still 40 minutes away, Kosiba sees a chance to grab an updraft sample. She gives Nesbitt a new mission: stop eating ice cream, and throw a balloon into one of the deepening clouds heading his way. Nesbitt’s team piles into the truck and heads west. He has goosebumps and tells himself to slow down as he drives through the sun-bleached pastel shops of Río Tercero. As they leave town, they see that the clouds ahead of them have grown tall enough to block the sun, casting shifting shadows on the fields. “Target in sight,” Nesbitt relays over WhatsApp. The road begins to curve away from the clouds, and Nesbitt pulls onto the shoulder. It isn’t an ideal spot — there is a barbed wire fence and power lines, which could snare his balloon — but the clouds are floating north and will soon be out of range. Nesbitt’s team inflates the balloon as gusts ripple across the field. When the balloon reaches the size of an exercise ball, Nesbitt unhooks it, walks to the fence, and shoves it clear of the powerlines. Its sensor swinging, the balloon drifts up and then curves sharply north, caught in the updraft, and is sucked into the underbelly of the darkening cloud.

Huddling around their laptop, the team watches as the readings for humidity and temperature converge: they’d made it into the cloud. Their detour a success, Nesbitt’s team jumps back in their truck and hurries south before the storm can break. Back at the hotel, Varble watches the cameras at the hilltop site. He sees one cloud along the ridge bubble upward then subside, only to have another one appear two miles east, as if it had teleported. At first, the scientists think this cloud, too, will fade. But it shoots upward and keeps going. Its top freezes and grows hazy, forming an anvil. Varble alerts the field teams that a storm has formed not on the plains, as they had expected, but farther north along the ridge. Kosiba tells the radars to start scanning the area. It’s bad luck for Schumacher, who had just driven under that cloud on his way south. Kosiba tells him to turn around and try to get ahead of it. As he passes under the cloud once more, hail clatters off his windshield. As Schumacher is driving, the storm explodes upward with such force that it punches through the tropopause and forms a white dome in the stratosphere. The researchers in the ops center watch the satellite feed as the cloud pushes into the jet stream, sending out a frozen wake like a rock in a fast-flowing river. A few researchers leave their desks and run to the hotel’s rooftop deck, where the cloud is now visible over the mountains as a bright white cliff. It has taken only 20 minutes to go from a benign cumulus to a “supercell,” an extremely powerful thunderstorm that can move in unpredictable ways.

Now north of the storm, Schumacher pulls onto a dirt road and starts inflating a balloon, but the storm lurches east. His team jumps back in the van and gives chase. They bounce down the rutted road as the storm churns ahead of them, drawing up twisting ropes of dust. Kosiba alerts them that it has begun to show tornado-like rotation. “We’re trying our best to catch it,” Schumacher replies. “Not sure we’ll be able to.” He comes to a stop once more. His students start inflating the balloon. One of them unhooks it from the nozzle and runs to the middle of the road, holding the balloon over his head with both hands as it pulls and distends in the wind. He lets go, but once again, the storm jumps away, and the balloon sails north into a sky that is already patched with blue. But in veering away from Schumacher, the storm flies directly through the line of radar trucks that have been waiting since the morning. The researchers inside secure their doors as it approaches and triple-check their radars. Hovering above the plain, the storm looks like a dark jellyfish, the sky around it blue, but everything beneath it is hazy with hail and dust and lit by strobes of lightning. The radars are in the perfect position to scan its heart as it passes over, pelting the trucks with dirt and vegetation. As it cuts between the two southernmost radars, baseball-sized hail hammers the new radar Nesbitt had lounged in front of two hours earlier, bashing craters into its pristine shell. And like that, the storm is gone, churning east, leaving tattered scud clouds drifting along the ground, and dark shapes keeling at odd angles in the sky. The air is cooler and smells of copper and cut grass. “That thing was generating the biggest dust storm/haboob I’ve ever seen,” Schumacher writes in WhatsApp. Nesbitt drives north and runs into Schumacher, and the two teams head back toward headquarters, watching new clouds build and darken and move off the mountains to their west. The scientists at the hotel direct the drivers to pause, then drive, then pause, as they frogger through the drifting storms. A lowering funnel cloud appears to their left and Nesbitt considers giving chase, but the message comes back from headquarters to return home: they’d gotten everything they need.

Steve Nesbitt: It’s looking “lit” from the south Jim Marquis: Execellent data collection today, everyone! Jeff Trapp: thanks indeed!

Back at the hotel, the researchers marvel at their luck, replaying the satellite feed and congratulating the field teams filing in, dusty, exhausted, and smiling. Schumacher’s updraft balloons had missed, but Nesbitt had scored a lucky hit during his detour earlier in the afternoon. Luckier still, the storm had formed right above the hilltop site, in range of its dozens of sensors. It then traveled through the center of the mobile radar network. It might be one of the best recorded supercells ever, Nesbitt says. “PhD theses will be written about this storm for decades.” They could slice the cloud any number of ways. At its peak, it was about 25 miles across and poured down 1.6 million gallons of water per minute, more than enough to fill two Olympic-sized swimming pools. Floating above the plains, it contained 10 trillion drops of water and ice, including hailstones the size of tennis balls, thrown six miles above the Earth by 90 mile-per-hour updrafts. Once they checked the radar, the researchers could see that the swirls of dust they had witnessed were created by vortices just shy of meeting the windspeed definition of a tornado. (Still unclear to the researchers: why did it teleport off the mountain? What, ultimately, caused this cloud and not the others to grow into a storm?) There were, in total, about 10 terabytes of data on its 3.5-hour life, too much to simply upload. It would have to be put on a hard drive, carried by hand onto a plane, and taken back to the lab where, the hope was, other scientists would use it to untangle the mysteries of cloud behavior or train their models to mimic it. At his most ambitious, Varble’s hopes for what this research might accomplish can seem modest. “If we could help someone bring down the uncertainty by half a degree, help people adapt a bit, that would be worthwhile,” he says.

How Clouds Affect Climate 1. Basics Clouds both cool the Earth by reflecting sunlight and warm it by absorbing infrared radiation from the planet’s surface. Depending on a cloud’s thickness, height, and reflectivity, one effect will win out over the other, resulting in a net warming or cooling. 2. High clouds High clouds are expected to move higher as the climate warms, where they will emit less heat into space, worsening warming. 3. Low clouds Low clouds reflect a great deal of sunlight, and how they will change is a major wildcard. Satellite observations and models suggest that a warming planet will cause these clouds to thin and break up. 4. Poleward movement Clouds appear to be moving toward the poles, where they will reflect less solar radiation, warming the Earth. 5. Changing rainfall As cloud patterns change, rainfall zones are expected to both shrink and shift. For some regions, this will mean drought; for others, floods.