It just seems like a beautiful day in Southern California,” Bryan Caforio said.

It was late January in Porter Ranch, an affluent neighborhood on the northern fringe of Los Angeles. Caforio and I sat at a Starbucks overlooking an oceanic parking lot crowded with shoppers. The air was still, dry, 70 degrees. Caforio, a young trial lawyer running for Congress in the state’s 25th District, gestured at the pink and orange striations of sky above Aliso Canyon, its foothills bronze in the falling daylight. “It seems like a beautiful sunset in a wonderful community,” Caforio said, “and we’re sitting outside, enjoying a wonderful coffee.”

But there were scattered clues that suggested that everything was not so wonderful. Near a trio of news vans parked in front of the Starbucks, antenna masts projecting from their roofs, a cameraman stared quizzically up at the canyon. Next to the SuperCuts, security guards stood outside two nondescript storefronts; stenciled on the windows were the words “Community Resource Center” and, in smaller letters, “SoCalGas.” The guards asked for identification and dismissed anyone who tried to take a photograph. At the entrance to Bath & Body Works, a device that resembled an electronic parking meter was balanced on a tripod; the digital display read “BENZENE,” followed by a series of indecipherable ideograms. The parking lot held a preponderance of silver Honda Civics bearing the decal of the South Coast Air Quality Management District. Inside the cars, men sat in silence, waiting.

Beyond the Ralphs grocery store and the Walmart rose a neighborhood of jumbo beige homes with orange clay-­tiled roofs and three-car garages. The lawns were tidily landscaped with hedges of lavender, succulents, cactuses and kumquat trees. The neighborhood was a model of early-­1980s California suburban design; until October, it was best known for being the location where Steven Spielberg shot “E.T.” But now the meandering streets were desolate, apart from the occasional unmarked white van. As you ascended the canyon, reaching gated communities with names like Renaissance, Promenade and Highlands, the police presence increased. On Sesnon Boulevard, the neighborhood’s northern boundary, an electric billboard propped in the middle lane blinked messages: “REPORT CRIME ACTIVITY; L.A.P.D. IN THE AREA; CALL 911.” Holleigh Bernson Memorial Park was empty aside from three cop cars, patrol lights flashing.

But the most significant clues were the spindly metal structures spaced along the ridge of the canyon. They resembled antennas or construction sites or alien glyphs. Until recently, most residents of Porter Ranch did not pay them much attention.

“You look at the hills, you see a few towers,” Caforio said. “But do you really know what they are?” He shook his head. “You try to say, ‘Hey, we’re having an environmental disaster right now!’ But it just looks like a beautiful sunset.”

The first sign of trouble came on Oct. 25, when the Southern California Gas Company filed a terse report with the California Public Utilities Commission noting that a leak had been detected on Oct. 23 at a well in its Aliso Canyon storage facility. Under “Summary,” the report read: “No ignition, no injury. No media.”

The local news media began to take notice, however, when Porter Ranch residents complained of suffocating gas fumes. In response, SoCalGas released a statement on Oct. 28 pointing out that the well was “outdoors at an isolated area of our mountain facility over a mile away from and more than 1,200 feet higher than homes or public areas.” It assured the public that the leak did not present a threat.

Timothy O’Connor, the director of the Environmental Defense Fund’s California Oil and Gas Program, had read about the complaints. But he did not think much of them until Nov. 3, when, at a climate-­policy event in downtown Los Angeles, he learned from an acquaintance who worked at SoCalGas that the company was flying in experts from around the country to help plug the leak. At home that night, O’Connor read everything he could about the Aliso Canyon gas field. How much gas was stored inside the canyon? How much could leak out?

The foothills on which Porter Ranch was built, O’Connor learned, once belonged to J.Paul Getty. His Tide Water Associated Oil Company hit crude in 1938 and did not sell the land until the early 1970s, after it had extracted the last drop. The drained oil field was bought by Pacific Lighting, which used it to store natural gas. With a capacity of 84 billion standard cubic feet, the cavity, which lies between 7,100 and 9,400 feet below the surface, is one of the country’s largest reservoirs of natural gas (which is composed mainly of methane). The facility functions as a kind of gas treasury. When prices are low, the company hoards the gas inside the canyon; when they are high, it releases the gas into pipelines that snake through Los Angeles, heating homes, fueling stoves and providing power to solar-­and ­wind-­energy facilities.

The 115 wells in Aliso Canyon can be imagined as long straws dipping into a vast subterranean sea of methane. The leaking well, SS-25, is a steel tube seven inches in diameter that descends 8,748 feet from the canyon’s ridge. The well is plainly visible from many of the streets in Porter Ranch. From the ground, it resembles a derrick, set beside a series of low white buildings. If you look at it through a pair of binoculars, you can make out, flying from its highest girder, an American flag.

After conducting some basic calculations, O’Connor arrived at a shocking conclusion. Given the pressure and quantity of gas stored within, the canyon was like an overinflated balloon; a puncture could release in a single day as much gas as 1,785 houses would consume in a year. As it turned out, O’Connor was mistaken — the figure ended up being much higher than that — but he included it in an urgent letter he sent the next day, on Nov. 4, to the governor’s senior energy adviser and members of the California Air Resources Board, Public Utilities Commission, Energy Commission and Department of Conservation. He demanded that the agencies conduct “an accurate and public accounting of the gas lost at Aliso Canyon.”

That evening, O’Connor attended a hearing at the Community School in Porter Ranch with about 100 panicked residents. They complained that the gas fumes were causing headaches, respiratory problems, nosebleeds and vomiting. The next morning, having yet to receive a response to his letter, O’Connor realized that he didn’t have to wait for the state to take action. He could call Stephen Conley.

Conley is an atmospheric scientist at the University of California, Davis, and the founder of Scientific Aviation. He flies a single-­engine Mooney TLS that looks like something Cary Grant might have flown in “Only Angels Have Wings.” Public agencies, scientists and nonprofit organizations that study the climate hire Conley to loop over oil and gas fields at low altitudes, measuring methane concentrations with a device called a Picarro analyzer. At 10:30 a.m. on Nov. 5, Conley took off from Lincoln Regional Airport, just north of Sacramento. As a courtesy, O’Connor notified Jill Tracy, the director of environmental services at SoCalGas. He began to receive a flurry of text messages from executives at SoCalGas. They said the flight was unsafe and inappropriate. But SoCalGas was not concerned for the safety of the pilot, as O’Connor first assumed. The executives claimed to be concerned for the workers on the ground, who were operating cranes and drills in an effort to plug the leak. The workers, Tracy wrote, might become distracted by the sight of an airplane overhead, with catastrophic consequences.

O’Connor found this reasoning odd, because Porter Ranch lies in the flight path of Van Nuys Airport. Nearly 600 flights take off or land there every day. He proposed that the airplane keep one mile away from the well site. SoCalGas executives said they still considered this unsafe. O’Connor asked whether there was a safe distance from the well at which the airplane could fly. The company said there was not. Conley was forced to turn back.

Two days later, though, Conley was back in the air, this time on assignment for the California Energy Commission. Over the course of the next four months, Conley flew 15 flights over the site. On his first flight, Conley’s Picarro analyzer registered 50 parts per million. The normal concentration of methane in the atmosphere is two parts per million. Conley thought something was wrong with the instrument. But a backup analyzer gave the same reading. He recalled, “That’s when I said, Oh, my God, this is real.”

What is real to a climate scientist is abstract to the rest of us. The study of the climate is a study of invisible gases. In order to translate findings to a public lacking a basic understanding of atmospheric chemistry, climatologists must resort to metaphor and allegory. They must become writers, publicists, politicians. This doesn’t always come easily. The leak at Aliso Canyon, Conley discovered, was the largest methane leak in the country’s history. But what did that mean?

You could begin by comparing emissions from the gas leak at Aliso Canyon with other pollution sites. Conley had logged about 1,500 hours of flight time over oil and gas fields, moonscapes like the Barnett and Eagle Ford Shales in Texas, the Julesburg Basin in Colorado and the Bakken Formation in North Dakota. The highest methane-emission rate he had ever recorded was three metric tons per hour. The methane was leaking from Aliso Canyon at a rate of 44 metric tons per hour. By Thanksgiving, it had increased to 58 metric tons per hour. That is double the rate of methane emissions in the entire Los Angeles Basin. This fact takes some effort to absorb. It means that the steel straw seven inches in diameter plugged into Aliso Canyon was by itself producing twice the emissions of every power plant, oil and gas facility, airport, smoke stack and tailpipe in all of greater Los Angeles combined.

In a paper published in the February issue of Science, Conley and his co-­authors estimate that 97,100 metric tons of methane escaped the Aliso Canyon well in total. Over a 20-year period, methane is estimated to have a warming effect on earth’s atmosphere 84 times that of carbon dioxide. By that metric, the Aliso Canyon leak produced the same amount of global warming as 1,735,404 cars in a full year. During the four months the leak lasted — 25 days longer than the BP oil spill in the Gulf of Mexico — the leak contributed roughly the same amount of warming as the greenhouse-­gas emissions produced by the entire country of Lebanon. If well SS-25 were a nation-­state, it would have contributed to global climate change at a rate exceeding that of Senegal, Laos, Lithuania, Estonia, Zimbabwe, Albania, Brunei, Slovenia, Nicaragua, Panama, Jamaica, Latvia, Georgia, Guinea, Equatorial Guinea, Costa Rica, Honduras, Tajikistan, Armenia and Iceland. SS-25 would rank just behind Mali.

These facts, despite their world historical significance, still failed to make much of an impression locally and nationally, let alone internationally. What was one more airborne toxic event at a time when the global climate was itself an airborne toxic event? The World Health Organization has called climate change the greatest global health threat of the 21st century, an opinion shared by the United Nations, the Environmental Protection Agency and the National Institutes for Health, among others. By 2030, increased rates of heat stress, infectious-­disease transmission and malnutrition caused by climate change are expected to cause an additional 250,000 deaths a year. Yet as gargantuan as the Aliso Canyon emissions might be, their influence on the climate would have no immediate or direct effect on the lives of the residents of Porter Ranch. Residents were as concerned about the leak’s contribution to atmospheric warming in the years and centuries to come as everyone else on the planet — which is to say, not especially. We are already immersed in leaking invisible gases with largely invisible effects too overwhelming to control. What difference was another Lebanon’s worth of emissions?

The residents of Porter Ranch were very concerned, however, about what the inhalation of the gas might do to their brains and their lungs. Some residents found the smell of gas so overwhelming that they sealed their windows and doors and refused to go outside. Others could not smell the gas and experienced no symptoms. Sometimes those with severe symptoms and those without lived in the same household. In the absence of reliable information from SoCalGas or state agencies, the residents of Porter Ranch underwent their own transformation: They became amateur scientists, epidemiologists, sociologists, political theorists. They began to develop their own hypotheses.

“Yellow spots,” Charles Chow said, “are coming out of the atmosphere.”

I met Chow, a 76-year-old retiree with mirthful eyes and springy joints, in his driveway in late January. He was installing new shocks on his 1992 burgundy Cadillac Brougham Elegante. Beside the Cadillac was a 1986 Silver Spirit Rolls-­Royce. In the street, which is called Thunderbird Avenue, there was a 2002 Black Thunderbird. Chow pointed out the spots. They were about the size and color of a yellow split pea. They had appeared on the windshields of his cars, on the Cadillac’s vinyl roof, on the canyon-­facing windows of his home.

Chow first became concerned about the Aliso Canyon leak in October, when Chaka Khan, his Chihuahua-­miniature pinscher, began having severe respiratory problems. His wife, Liz, who is 73, began suffering chronic headaches, eye irritation and a sore throat. Her doctor said there was nothing he could prescribe her. The only thing she could do, he said, was to leave Porter Ranch. Most of their neighbors fled before Thanksgiving. On their block alone, Chow estimates that 15 households, mostly retirees, relocated. Since then, the Chows have driven four times a month to a vacation rental they share on the Baja Peninsula, 60 miles south of the border, “just to get out of the atmosphere,” Chow said. In the Mexican air, Liz’s symptoms vanished.

Chow was soon joined in his driveway by Rick Goode, a neighbor of 25 years with a slender build and a birdlike gait. Goode wanted Chow’s advice about legal representation: About two dozen plaintiff’s firms had descended on Porter Ranch since October, competing to sign as many clients as possible. What did Chow think of Robert Kennedy’s firm? Or Weitz & Luxenberg, which had sent Erin Brockovich to solicit clients? The previous week, Brockovich told reporters that she “started feeling kind of dizzy” within 10 minutes of arriving in Porter Ranch. Chow ruled her out.

“You don’t get sick that fast,” he said.

“I’ve been having terrible headaches,” Goode said. “Have you?”

“My wife has headaches every day, sore throats,” Chow said. “I don’t. We both live in the same house. Everybody is different.”

Liz returned from a doctor’s appointment. She removed her sunglasses to reveal a new cyst on her eyelid. She searched for a word to describe her general condition since October. “A malaise,” she said finally.

Barbara Weiler, 64, who was walking her dog very slowly several blocks away, first experienced the malaise in gym class. “You felt like you were lazy,” she said. “It was obvious when we were using the resistance bands. We felt like we didn’t want to work as much as we normally would.”

Paula Vasquez found the smell of gas so strong in late October that she was certain there was a leak inside her house. She hasn’t opened a window since. She and her family — she lives with her husband, their 33-year-old daughter and their 13-year-old grandson — have experienced bloody noses, blurred vision and nasal congestion. But Vasquez has also noticed other signs. She pointed to fruit trees in her neighbors’ backyard. “I see them picking lemons,” she said. “I don’t say anything, but I’m concerned for them. Is there gas in the fruit?”

She showed me photographs she made her grandson take on her cellphone while she was driving home on the Ronald Reagan Freeway. In the sky above Porter Ranch, a heavy funnel of clouds was lit neon orange.

“It looks like a big atomic cloud,” she said. Vasquez had a warm, cheerful manner; horror did not come naturally to her. “Creepy, huh? But I don’t know anything about science.”

We are a show-me species, wired to look for visible evidence of invisible harm. That impulse can lead a person to blame global warming for a hot day in February or, conversely, make a climate-­change denialist find vindication in a snowstorm. But the world’s largest natural-­gas leak has no known effects on clouds or lemons. (It may, however, create yellow dots. Michael Jerrett, the director of the Center for Occupational and Environmental Health at U.C.L.A., explained that the dots are most likely a residue of the petroleum-­laced slurry used to plug the leak.) The most dangerous threats to our species are precisely those that are most difficult to visualize: long-term, slow-­to-­emerge, amorphous. These threats include not only warming temperatures but also mutating viruses and political corruption and tend to be invisible, dimensionless and pervasive, like death. Like natural gas.

While the yellow dots were coming out of the atmosphere and staining the vinyl roof of Charles Chow’s Brougham Elegante, the planet was enduring the warmest January on record. It was the fourth consecutive month in which global temperatures beat historical averages by more than one degree Celsius, another novelty. This news, when publicized at all, tended to be accompanied by NASA’s map of the world, overlaid muddily with orange and red splotches denoting temperature increases; otherwise there appeared stock photographs of sunbathers on beaches or icicles melting. Then came February, the warmest month in recorded history. The threat to human civilization is advancing faster than ever before — the climate is warming faster than at any time in the last 65 million years — but all we can see are sunbathers and melting icicles.

All that the residents in Porter Ranch could see during those months of yawning uncertainty were empty streets and mysterious white vans. They were desperate for answers: Was the gas making them sick? How could they protect themselves? Who would be held responsible? The personal-­injury lawyers were well prepared. They offered clarity, assurance, optimism. They could predict, with confidence, the future — a profitable future for the residents of Porter Ranch. Since November, the firms had been holding weekly informational meetings at local churches and hotels. At each session, lawyers answered questions from the community, often for several hours at a time, and circulated client forms.

Rick Goode and the Chows attended one such meeting in late January, two days after their driveway conversation on Thunderbird Avenue. It was hosted by R.Rex Parris at the Hilton in Woodland Hills, about 10 miles south of Porter Ranch. R.Rex Parris belongs to a consortium of law firms that on Dec. 2 filed the first class-­action complaint against SoCalGas and its parent company, Sempra Energy, the nation’s largest natural-­gas utility, on behalf of thousands of Porter Ranch residents. The group’s news release anticipated that the leak would end up costing Sempra shareholders “well over $1 billion.” On this morning, about 20 community members sat at conference tables, grazing on the free coffee, doughnuts and bagels. A young lawyer, who seemed to have consumed a large quantity of the coffee, stood at the front of the room, delivering her sales pitch.

“Anything SoCal tells you,” she said, “don’t listen to it. Everything they say means nothing.”

She advised the residents to keep daily journals. They were to note each occurrence of a physical symptom or a gas smell and list all expenses incurred by relocation or illness. Someone asked whether he could qualify as a plaintiff even if he lived 10 miles from Aliso Canyon.

“Nothing’s been established yet,” the lawyer said. “I’ve heard between five and 10 miles. But we don’t have the data yet.”

“They claim it started on Oct. 23,” one older woman said. “But in April, my dog, a boxer, died within two weeks. I know it was the gas.”

“It was earlier than Oct. 23,” the lawyer said. “I just don’t know when. We want it to be as early as possible, so we can get much more money for everyone.”

The residents nodded in approval.

The lawyer explained that about 30 attorneys were assigned to the case. The firms would receive as their fee 30 percent of any payouts. “We’re predicting a settlement,” she said.

A Russian man who resembled Gérard Depardieu exclaimed, “I escaped Chernobyl for this!”

The man, Igor Volochkov, later told me that in 1986 he moved from Kiev, 60 miles south of Chernobyl, to Los Angeles when his wife was pregnant with their son. “We ran away to save our lives and the lives of our children.”

Volochkov said he knew something was wrong in October, when his parrot, Bon, dropped dead. He bought a new parrot and a parakeet, Gosha and Margosha, but they died within a month. The same thing happened in Kiev, when, he said, nuclear radiation from Chernobyl killed his parakeet, Petruschka. Volochkov said his son had asked why they moved from one Chernobyl to another Chernobyl.

“Maybe,” Volochkov replied, “our destiny is to fight against Chernobyls.”

In mid-­november, nearly a month into the leak, the Los Angeles County Department of Public Health ordered SoCalGas to pay for new housing for anyone affected by the gas odors. Nearly 6,000 households, about half of Porter Ranch’s population, accepted the offer, moving to hotels, apartments and houses in surrounding neighborhoods. Those who did not relocate immediately struggled to find available short-term rental properties, but others took advantage of the gas company’s largess. Charles Chow said he knew a family paying $10,000 in monthly rent. “People are gouging the gas company,” he said. “I don’t believe in unfair practice. I was a businessman. I think fair is fair. All I might take is reimbursement for money I’ve had to pay the vet for Chaka Khan.”

Jerry McCormack, another neighbor of the Chows, has rarely detected an odor and has not been sick. “I think there’s a lot of foolishness going on,” he said. “This is not Fukushima. The rental market has gone crazy. Everyone is out to get the gas company. The hysteria is proportional to the number of lawyers coming to town.” He conceded that his wife, who is recovering from cancer, “can smell it quite well” and is concerned. Her oncologist advised her to leave.

Adam and Mindi Grant, a couple in their mid-40s, live a mile from the leak site. Their three children play basketball and swim outside. “We’ve legitimately smelled it one day,” Adam said. “We joke about it. Every time someone gets a bloody nose, we say, It’s the gas!”

Adam teaches world history at a local high school. Mindi is an insurance lawyer. “I have friends with real symptoms,” she said. “Some, maybe not. They’re setting up for a money grab. They think there’s big money, deep pockets. But they’re going to have trouble showing causation.”

“Had the smell been horrific,” Adam said, “we would have relocated. But because it’s not affecting us as a family, I’m a little lackadaisical about it.”

If the smell of gas makes one person dizzy while the neighbor next door can’t smell anything, is one of them lying? If a man does not actually inhale gas but develops headaches and nausea anyway, is his suffering any less? Disaster psychiatrists call this phenomenon “somatization,” a word that has replaced “hysteria” and “psychosomatic,” terms now considered offensive. “In man-made disasters, the psychological consequences can be very severe and ongoing,” David Eisenman, the director of the Center for Public Health and Disasters at U.C.L.A., told me. “Unexposed individuals can have symptoms similar to people who have exposure.” Fear makes you sick. As it turns out, inhaling poisonous gas causes the same symptoms as the fear of inhaling poisonous gas: headaches, dizziness and nausea.

Porter Ranch residents had reason to be afraid. Nobody could tell them what they were breathing. Methane was gushing from the leak, of this they could be certain, but methane was not what they smelled. Methane is odorless. What they smelled were mercaptans: sulfur compounds that in nature are released in animal feces. Mercaptans are added to natural-­gas pipelines to provide an olfactory alarm in case a leak occurs, the way banks insert exploding dye packs into bags of cash. Inhalation of mercaptans can cause headaches, dizziness and nausea, but like methane, they are not currently known to cause significant long-term health effects. The main health concern about the leak was that other, more toxic gases might also be escaping from the bowels of Aliso Canyon — including gases remaining from its previous life as an oil field.

Chief among these was benzene, a known carcinogen. Los Angeles air, among the most polluted in the nation, tends to have a background concentration of benzene between 0.1 and 0.5 parts per billion. The World Health Organization has declared that “no safe level of exposure can be recommended.” In November, readings taken by SoCalGas near its facility found benzene concentrations fluctuating wildly between 0.3 p.p.b. and a nightmarish 30.6; readings taken by the company in Porter Ranch shot as high as 5.5 p.p.b. Other toxic gases — toluene, xylene, hexane and hydrogen sulfides — were also detected at higher-­than-­normal concentrations. The South Coast Air Quality Management District tested the air in Porter Ranch during the first two months of the leak, but the monitoring was sporadic and conducted at only a handful of locations. By mid-January, after efforts to depressurize the well had managed to reduce the leakage rate considerably, a more rigorous study by Michael Jerrett of U.C.L.A. found that the air in Porter Ranch was in fact unusually clean — most likely because of the absence of so many residents and their cars.

California health officials believe that there will be no long-term health effects from the leak. “Increased cancer risk is very small,” said Dr. Melanie Marty, the acting deputy director for scientific affairs for California’s Office of Environmental Health Hazard Assessment. “Much smaller than routine risks we experience every day.” But Jerrett suspects that during the first six weeks of the leak, when the gas escaped at a much higher rate, conditions might have been dangerous, particularly for children and older residents. On March 10, following complaints from relocated residents who suffered nosebleeds and skin rashes after moving back home, Jerrett took dust samples at seven houses in Porter Ranch. Two contained benzene and hexane, a finding that Jerrett found “concerning.”

The actual composition of the gas was only the beginning of what the residents of Porter Ranch did not know about the invisible fumes seeping from Aliso Canyon. They did not know how far the gas was drifting or in what quantities. It seemed that the smell was stronger the higher you went up the mountain and stronger at dusk and dawn, but there was little data to support this. There was also the mystery of the complex local wind patterns, which resemble those of no other part of the Los Angeles Basin and change direction capriciously.

No one even knew what had caused the leak in the first place, though a broken safety valve, removed by SoCalGas in 1979 and never replaced, received some blame. In 2012, President Obama signed a pipeline-­safety bill that should have prevented a leak of this kind. “We have the law, but no one is complying,” said Mel Reiter, the editor of The Valley Voice, a monthly newspaper that may be the only local business to profit from the leak: More plaintiffs’ law firms sought full-page ads than it has pages. “There are 115 active wells, and more than two-thirds were built before 1980,” Reiter said. “If one is leaking, what are the odds that 30 more are, or will soon?”

Regulations are in place, but nobody knows who can enforce them. When Matt Pakucko, a lead plaintiff in the class-­action lawsuit, first smelled the leak on Oct. 24, he called SoCalGas. He said he was told that the company was merely “releasing gas into the air,” which was “something that they do periodically,” and that there wasn’t a leak. He knew that the South Coast Air Quality Management District was responsible for investigating air-­quality complaints. But SoCalGas, a private utility, did not fall under the regulatory oversight of any single agency. Besides the Air Quality Management District, agencies responsible for responding to the leak included the State Energy Commission; the Los Angeles County Department of Public Health; the Air Resources Board; the Public Utilities Commission; the Division of Occupational Safety and Health; the Department of Conservation’s Division of Oil, Gas and Geothermal Resources; the Environmental Protection Agency; the Office of Environmental Health Hazard Assessment; the County Fire Department; and the Governor’s Office of Emergency Services. In January, the Los Angeles County Board of Supervisors called for the creation of yet another regulatory “structure,” to oversee gas-­storage facilities.

For most Porter Ranch residents, all this confusion added up to a single fact: An invisible gas was threatening their lives. “We don’t know what methane is,” said Sam Kustanovich, a Belarussian pawnbroker who had the misfortune of buying his house two months before the leak was detected. “Nobody knows. It could mean explosions. Me, I’m afraid of explosions.”

The global climate, even in drought-­stricken Southern California, is not an especially consequential campaign issue. A menacing disaster that causes mass vomiting and mass nosebleeds in a wealthy, vote-rich community, however, is a candidate’s dream. In this election season, the procession of scientists and lawyers heading to Porter Ranch has been trailed by a caravan of Californian politicians. None have come out in favor of mass nosebleeds. Though the 25th Congressional District reaches only its pinkie toe into Porter Ranch, Bryan Caforio, a Democrat, has made the leak a central issue of the election, which promises to be one of few closely contested races in the House. The Republican incumbent, Steve Knight, who has received campaign donations from Sempra Energy, said in December that he was confident that SoCalGas was “working on this as diligently as they can” but more recently called for a congressional hearing on the matter and introduced safety regulations for natural-­gas storage. Even a Los Angeles County supervisor, Michael Antonovich, a Republican who has voted consistently against regulation efforts, has loudly proclaimed his determination to hold SoCalGas responsible.

“We’re all kind of feeding on it in a weird way,” said Henry Stern, a Democrat who is running for State Senate in the local district. He previously served as senior counsel on energy and environmental policy for the district’s current senator, Fran Pavley, a Democrat who cannot run again because of term limits. “How often are there climate disasters in suburbia?”

Stern has been struck at community meetings by the comments of local residents, many of them self-­identifying conservatives, who have begun to question the wisdom of relying on fossil fuels. “Climate change is not a real thing for most of these people,” Stern said. “But you change your mind quick when your kids are puking.”

The only politician who has failed to use the gas leak for political gain is Gov. Jerry Brown. His Office of Emergency Services, following protocol, began monitoring the leak in October and began coordinating the state’s response in mid-­November, overseeing the various state agencies responsible for responding to it. On Dec. 18, Brown, a Democrat, sent a stern letter to the chief executive of SoCalGas, urging cooperation and demanding accountability. “Everything that could be done under the authority of the governor was being done,” Mark Ghilarducci, the director of the Governor’s Office of Emergency Services, told me. But Brown did not visit Porter Ranch until January, when he toured the SoCalGas facility and met privately with four members of the local Neighborhood Council; this was 11 weeks into the leak and nearly a month after he attended the United Nations climate talks in Paris, where he boasted of California’s emissions-­reduction plan, the most ambitious in North America. Brown declared a state of emergency in Aliso Canyon on Jan. 6, but for many in Porter Ranch, that wasn’t nearly soon enough.

“We’re suffering because Jerry Brown is so not involved in this,” Matt Pakucko said. “There he was in Paris, saying look how green California is, while 10 years of green stuff is going into the air right now.”

Ghilarducci disputes this. “This concept that nothing happened and the governor was not engaged until he issued a state of emergency on Jan. 6 is just absolutely not correct,” he said. “Let’s face it: We deal with so many emergencies out here. This is not Vermont, this is not Oklahoma. … This is a nation-­state.” He continued, “The governor is very confident that he doesn’t need to be on the scene, holding a press conference, to show that he’s doing something.”

The governor’s reputation in Porter Ranch was not helped by the revelation that his younger sister, Kathleen Brown, is a paid board member of SoCalGas’s parent company, Sempra Energy. “I’m sure there’s a conflict of interest,” Rick Goode said. “My feeling is it’s an ‘I scratch your back, and you scratch mine.’ It concerns me.” In 2013 and 2014, Kathleen Brown received $456,245 in compensation, including stock awards. A partner at the firm of Manatt, Phelps & Phillips, she also has, according to the Public Accountability Initiative, a $949,653 stake in the Forestar Group, a real estate and natural-resources company, where she is a director and major shareholder. Forestar is developing Hidden Creeks Estates, a gated community of 188 luxury homes, right next to Porter Ranch, on property abutting Sempra’s.

Kathleen Brown’s office at Manatt referred me to Doug Kline, the director of corporate communications for Sempra Energy. He would not give a specific comment on Brown’s role, but he did say, “Our board of directors has been actively engaged and regularly briefed on the Aliso Canyon incident.” Deborah Hoffman, Jerry Brown’s deputy press secretary, wrote in a statement that any implication that the state did not exercise “its full regulatory and oversight authority” was “scurrilous and irresponsible.”

SoCalGas announced on Feb. 18 that the well had been sealed. Chris Gilbride, a spokesman for SoCalGas, wrote in an email, “Throughout the incident, air samples for benzene and other compounds were found to be at or near levels seen in the rest of the county and below levels of concern.” He continued, “The Los Angeles County Department of Public Health has consistently reported that no long-term health effects are expected due to the leaking well.” In late February, many residents, including Rick Goode and Igor Volochkov, said they still smelled gas or still suffered symptoms. “Maybe SS-25 is capped,” said Kyoko Hibino, Matt Pakucko’s girlfriend. “But I think there is still something seeping up from underground. I think other wells are continuing to leak. The smell is still pretty strong. It is out there still.”

It is uncertain whether the residents of Porter Ranch will experience health effects in the long term. It is certain that the atmosphere will experience long-term effects. But the effects will be as indecipherable as a plume of colorless gas leaked into a windswept canyon. How do we make sense of the addition to the atmosphere of thousands of tons of invisible gases that will have semi-­invisible effects on us and only slightly more visible effects on generations we won’t live to see?

“If you compare the Aliso Canyon leak to other leaks,” said Stephen Conley, the aviator-­scientist, “it’s top dog. It’s a monster. It throws off L.A.’s emissions for the year. It’s a significant percentage of California’s annual carbon budget. But it’s about 0.002 percent of the global methane budget. It’s not like next year will be warmer because of Aliso Canyon.”

This is true. It’s not like next year will be warmer because of the car trips that Porter Ranch residents make to their temporary rental homes, or the gas they use to cook dinner, or the energy required to heat their swimming pools. Next year won’t be warmer because of the 200,000 airplanes passing through Van Nuys Airport. Next year won’t even be warmer, necessarily, because of the roughly 140 billion cubic meters of natural gas that oil companies flare into the atmosphere. But next year will be warmer.