For years, as oil and gas companies increased production, they hired lots of workers, enriching communities across the United States. That is no longer true. The country is pumping more oil than ever and near-record amounts of gas. But the companies that extract, transport and process these fossil fuels employ roughly 25 percent fewer workers than they did a decade earlier when they were churning out less fuel, according to a New York Times analysis of federal data. Now, with some worried about a looming oversupply of oil, producers are tightening their belt, with spending across North America expected to fall 3 percent this year, according to Barclays. That raises the specter of further job losses, even as President Trump urges companies to “drill, baby, drill.” The thinning out of American oil and gas jobs is reminiscent of the long decline of the U.S. coal industry, where employment crested decades before production fell as mining companies extracted more rocks with fewer people. Advertisement SKIP ADVERTISEMENT Two decades into the shale boom, companies are drilling wells that extend deeper into the earth, unlocking more oil and natural gas. New technology is letting them oversee drilling, fracking and production from afar, with fewer people on-site. And larger companies are snapping up smaller players, shedding accountants, engineers and other workers as they go. While the total number of jobs has increased from the bleakest days of the pandemic, far fewer people are working in the industry than before Covid. Among the cost-cutting techniques being pursued by Exxon Mobil and Chevron: hiring engineers and geologists in India, where labor is cheaper, to support activities in the United States and elsewhere. The decline in oil and gas work also reflects the continuing transition to cleaner forms of energy, even if that shift is happening more slowly than many analysts had anticipated a few years ago. “You won’t see a lot of job growth in just the basic act of producing oil and natural gas,” Chris Wright, chief executive of the oil field services company Liberty Energy, said in an interview before Mr. Trump tapped him to lead the Energy Department. The industry, Mr. Wright said, is “on a trend now of flat to maybe gradually declining employment.” Mr. Trump will “protect our energy jobs” while lowering costs for consumers, said Karoline Leavitt, a spokeswoman. During the first half of the American fracking boom, oil and gas companies added workers at a much faster clip than other industries. The industry nearly doubled in size over 10 years, turbocharging the economies of places like North Dakota, home to the Bakken shale formation. Then, in 2014, oil prices crashed. It took a couple of years, but U.S. production eventually bounced back, soaring to a record of nearly 13.5 million barrels a day last fall. Employment never fully recovered, though, entering an undulating decline punctuated by booms and busts, most recently during the pandemic, when oil prices briefly plunged below zero. Matthew Waguespack was fracking a well in early 2020 when a representative for the oil company that had hired his team to do fieldwork walked into the crew’s mobile office in eastern New Mexico. Advertisement SKIP ADVERTISEMENT “Pump all your sand, pump all your chemicals, pack up,” Mr. Waguespack recalled the man telling the team. “And get out of here.”

Harold G. Hamm, the billionaire oil and gas executive who helped bankroll Donald J. Trump’s campaign and stands to profit from his energy policies, is hosting an exclusive fossil fuel industry celebration on Inauguration Day. The daytime party on the roof of the historic Hay-Adams Hotel, a block from the White House, will be a moment of triumph for Mr. Hamm, who poured more than $4.3 million into political action committees supporting Mr. Trump. Mr. Hamm, the founder of Oklahoma-based Continental Resources, has been influential in Mr. Trump’s plans to gut environmental protections and allow unfettered access by energy companies to federal land and waters. He also helped raise money from others in the oil and gas industry, which spent more than $75 million on efforts to elect Mr. Trump. Among the invited guests to Mr. Hamm’s celebration is Doug Burgum, Mr. Trump’s pick to run the Interior Department. Mr. Burgum’s term as governor of North Dakota ended last month and if he is confirmed, he would help determine the use of public land and federal waters. He is also Mr. Trump’s choice to run a government-wide energy council. Mr. Burgum received an invitation to the celebration from Mr. Hamm’s executive assistant two weeks after Mr. Trump’s victory in the November election. Advertisement SKIP ADVERTISEMENT Rob Lockwood, an adviser to Mr. Burgum, said in a statement that Mr. Burgum would not attend Mr. Hamm’s party and would instead participate in “formal inauguration proceedings” on Jan. 20. Top sponsors of the Jan. 20 event listed on the invitation include the Domestic Producers Energy Alliance, a lobbying group that Mr. Hamm founded to aggressively fight climate change policies, and Unleash Energy, a conservative group that includes many advisers to Mr. Trump. “Enjoy a remarkable experience to commemorate this momentous occasion with panoramic views of the White House and a vibrant atmosphere of celebration,” read a typed note from Mr. Hamm to Mr. Burgum accompanying the invitation. “This will be a memorable gathering of friends, supporters, and special guests. We look forward to celebrating this pivotal moment with you!” The documents were obtained by Fieldnotes, a research group that focuses on the oil and gas industry, through a public records request and were reviewed by The New York Times. Campaign finance experts said the private event did not appear to violate ethics rules. Administration officials and nominees can join widely attended receptions so long as they only accept the same food and refreshments as offered to other guests. But many also noted that few others than big donors can get the chance to privately chat up the people who will be influencing America’s energy policy over the next four years. “This is an invite-only, high-dollar event for folks seeking access to the incoming Trump administration,” said Tyson Slocum, who directs the energy program at Public Citizen, a watchdog group. Even if Trump officials do not attend, “You are basically getting the ear of the president,” Mr. Slocum said. “You have access to Harold Hamm, who is at the back shoulder of Donald Trump, dictating the priorities of the American oil and gas industry.” Mr. Hamm and Continental Resources, the largest oil producer in North Dakota’s Bakken field, did not respond to requests for comment. Others sharing the cost of Mr. Hamm’s party include Liberty Energy, the gas services company founded by Chris Wright, who is Mr. Trump’s pick to lead the Energy Department. Mr. Wright is expected to step down from the company when he is confirmed by the Senate. Summit Agriculture Group, the parent company of Summit Carbon Solutions LLC, is also an event sponsor. Mr. Hamm is an investor in Summit Carbon Solutions, based in Iowa, which plans to build a $9 billion project to collect carbon emissions from ethanol plants in five states and send it by pipeline to North Dakota, where it would be buried underground. As governor, Mr. Burgum was a strong supporter of the project, which has run into opposition from landowners and local officials in several states. Summit Agriculture Group is run by Bruce Rastetter, who has donated to Mr. Trump and the Republican Party for years. Other sponsors include Devon Energy, an Oklahoma oil company with a long history of fighting climate regulation. Summit Agriculture Group and Devon Energy did not respond to requests for comment for this article. The American Petroleum Institute, the oil industry’s main lobbying group, is also a sponsor. “API regularly sponsors events with policymakers on both sides of the aisle to educate on the critical role of American energy in powering our economy and strengthening national security,” Andrea Woods, a spokeswoman for the American Petroleum Institute, said in a statement. During the 2024 campaign Mr. Trump asked oil and gas executives to raise $1 billion for his White House bid. At a dinner in April at his Mar-a-Lago resort in Florida, Mr. Trump promised about 20 oil and gas executives that they would save far more than that amount in avoided taxes and legal fees after he repealed environmental regulations, according to several people who were present and who requested anonymity to discuss a private event. The fossil fuel industry has reveled in Mr. Trump’s victory. Mr. Trump has promised a swift elimination of President Biden’s limits on pollution from automobile tailpipes, power plant smokestacks and oil and gas wells. He also pledged to boost American liquefied natural gas exports — which are already at record levels — and said he would allow drilling in the pristine Arctic National Wildlife Refuge and waive environmental regulations for companies that invest at least $1 billion in the United States. The United States is currently producing more oil than any nation in history, and is the world’s biggest exporter of natural gas. Still, the oil and gas industry is glad to see the Biden administration go, said Thomas J. Pyle, president of the American Energy Alliance, which supports fossil fuel energy development. “They’ve been hostile to domestic oil and gas production from day one, right up to the very end, and President Trump has made it clear that he sees the important role that this industry plays,” Mr. Pyle said.

From above the raging flames, these planes can unleash immense tankfuls of bright pink fire retardant in just 20 seconds. They have long been considered vital in the battle against wildfires. But emerging research has shown that the millions of gallons of retardant sprayed on the landscape to tame wildfires each year come with a toxic burden, because they contain heavy metals and other chemicals that are harmful to human health and the environment. The toxicity presents a stark dilemma. These tankers and their cargo are a powerful tool for taming deadly blazes. Yet as wildfires intensify and become more frequent in an era of climate change, firefighters are using them more often, and in the process releasing more harmful chemicals into the environment. Some environmental groups have questioned the retardants’ effectiveness and potential for harm. The efficiency of fire retardant has been hard to measure, because it’s one of a barrage of firefighting tactics deployed in a major fire. After the flames are doused, it’s difficult to assign credit. The frequency and severity of wildfires has grown in recent years, particularly in the western United States. Scientists have also found that fires across the region have become faster moving in recent decades. There are also the longer-term health effects of exposure to wildfire smoke, which can penetrate the lungs and heart, causing disease. A recent global survey of the health effects of air pollution caused by wildfires found that in the United States, exposure to wildfire smoke had increased by 77 percent since 2002. Globally, wildfire smoke has been estimated to be responsible for up to 675,000 premature deaths per year. Fire retardants add to those health and environmental burdens because they present “a really, really thorny trade-off,” said Daniel McCurry, an assistant professor of civil and environmental engineering at the University of Southern California, who led the recent research on their heavy-metal content.The United States Forest Service said on Thursday that nine large retardant-spraying planes, as well as 20 water-dropping helicopters, were being deployed to fight the Southern California fires, which have displaced tens of thousands of people. Several “water scooper” amphibious planes, capable of skimming the surface of the sea or other body of water to fill their tanks, are also being used. Two large DC-10 aircraft, dubbed “Very Large Airtankers” and capable of delivering up to 9,400 gallons of retardant, were also set to join the fleet imminently, said Stanton Florea, a spokesman for the National Interagency Fire Center in Boise, Idaho, which coordinates national wildland firefighting efforts across the West. Sprayed ahead of the fire, the retardants coat vegetation and prevent oxygen from allowing it to burn, Mr. Florea said. (Red dye is added so firefighters can see the retardant against the landscape.) And the retardant, typically made of salts like ammonium polyphosphate, “lasts longer. It doesn’t evaporate, like dropping water,” he said. The new research from Dr. McCurry and his colleagues found, however, that at least four different types of heavy metals, including chromium and cadmium, that were present in a common type of retardant used by firefighters exceeded California’s requirements for hazardous waste. Federal data shows that more than 440 million gallons of retardant were applied to federal, state, and private land between 2009 and 2021. Using that figure, the researchers estimated that between 2009 and 2021, more than 400 tons of heavy metals were released into the environment from fire suppression, a third of that in Southern California. Both the federal government and the retardant’s manufacturer, Perimeter Solutions, have disputed that analysis, saying the researchers had evaluated a different version of the retardant. Dan Green, a spokesman for Perimeter, said retardants used for aerial firefighting had passed “extensive testing to confirm they meet strict standards for aquatic and mammalian safety.” Still, the findings help explain why concentrations of heavy metals tend to surge in rivers and streams after wildfires, sometimes by hundreds of times. And as scrutiny of fire suppressants has grown, the Forest Service has set buffer zones surrounding lakes and rivers, though its own data shows retardant still inadvertently drifts into those waters. In 2022, the environmental nonprofit Forest Service Employees for Environmental Ethics sued the government in federal court in Montana, demanding that the Forest Service obtain a permit under the Clean Water Act to cover accidental spraying into waterways. The judge ruled that the agency did indeed need to obtain a permit. But it allowed retardant use to continue to protect lives and property.

Constellation Energy, the nation’s largest nuclear power plant operator, has agreed to buy another electricity producer, Calpine, for $16.4 billion, a deal that shows how fast-rising demand for power, partly a result of the data centers being built for artificial intelligence, is having far-reaching effects on the economy. The cash-and-stock deal, announced Friday, ranks among the power sector’s biggest, and indicates that natural gas is likely to play a larger role than many expected a few years ago in meeting the nation’s electricity needs. That could undermine efforts to address climate change unless companies quickly figure out how to capture and store emissions from gas power plants. The tie-up would broaden Constellation’s portfolio as companies like Microsoft, Google and Amazon are scrambling to secure energy for data centers used to run artificial intelligence and other services. Electricity demand is also increasing because of the building of new factories in the United States and greater use of electric vehicles and heat pumps. The growth is reshaping a traditionally sleepy industry that has not been accustomed to turbocharged growth. “Lots of people who were not paying any attention to electricity a year ago are now trying to figure out how to participate in meeting what seems to be inevitable growth in demand,” said Daniel Yergin, the vice chairman of S&P Global, who won a Pulitzer Prize for his book “The Prize: The Epic Quest For Oil, Money and Power.” Advertisement SKIP ADVERTISEMENT Calpine, which is based in Houston and privately held, operates a large fleet of natural gas power plants in several states as well as the Geysers geothermal energy complex in California. Constellation, which is based in Baltimore, said in a statement that it expected Calpine’s natural gas assets to help ensure the reliability of the electric grid. The combination also would broaden the company’s presence in Texas, where power demand is growing quickly, and add more renewable energy to its portfolio. “We believe that natural gas and geothermal, along with nuclear, will be critically important for the nation,” Joseph Dominguez, chief executive of Constellation, said on a call with investors and analysts on Friday morning. He added that it was important to ensure that energy resources were not only sustainable, but reliable as well. “We believe that natural gas and clean energy, blended together, will be very attractive to customers,” Mr. Dominguez said. Constellation’s stock price soared more than 20 percent in early trading on Friday and closed the day up 25 percent, an unusually large jump for an acquiring company. Its shares had already more than doubled over the past year as expectations for U.S. power demand growth rose. Constellation would pay $4.5 billion in cash and assume roughly $12.7 billion of Calpine’s debt as part of the deal. Nuclear power plants, which can operate around the clock without releasing planet-warming emissions, have been among the early beneficiaries of booming investment in artificial intelligence. Constellation agreed last year to spend $1.6 billion to restart a nuclear reactor at Three Mile Island near Harrisburg, Pa. — a project for which Microsoft is effectively footing the bill. But there are only a few mothballed nuclear plants that can be restarted. Some companies are also betting on new, smaller reactors, but those are not expected to begin producing meaningful amounts of power for at least several years if all goes well. As a result of those challenges, many energy and tech companies are increasingly looking to natural gas, even though its use releases carbon dioxide and methane, two leading greenhouse gases that are warming the planet. “It’s going to be hard for the utilities to provide the power that these data centers need without gas,” said Andrew Gillick, an energy strategist for the analytics firm Enverus. Advertisement SKIP ADVERTISEMENT Power demand from data centers is poised to increase 15 percent a year on average through the end of the decade, Goldman Sachs estimated last year. Andrew Novotny, chief executive of Calpine, said the combined company would be able to invest in new power generation. “Together, we will be better positioned to bring accelerated investment in everything from zero-emission nuclear to battery storage that will power our economy in a way that puts people and our environment first,” he said in a statement. A diverse group of power plants could let the new company be more effective in how it manages its resources, depending on how electricity needs change. Adding more natural gas to its portfolio would, however, expose Constellation to more risk related to fluctuating commodity prices, Enverus said. The deal with Constellation is the culmination of a big turnaround for Calpine, which had come under pressure in recent years as California and other states sought to move away from fossil fuels. A group of investors including Energy Capital Partners took Calpine private several years ago in a deal valued at $5.6 billion, not including debt. The companies said they expected the transaction to close within a year, subject to regulatory approvals. Constellation would address any potential concerns raised by antitrust officials about its market power by selling assets, Mr. Dominguez said.

America’s efforts to cut its climate change pollution stalled in 2024, with greenhouse gas emissions dropping just a fraction, 0.2 percent, compared to the year before, according to estimates published Thursday by the Rhodium Group, a research firm. Despite continued rapid growth in solar and wind power, emissions levels stayed relatively flat last year because demand for electricity surged nationwide, which led to a spike in the amount of natural gas burned by power plants. The fact that emissions didn’t decline much means the United States is even further off-track from hitting President Biden’s goal of slashing greenhouse gases 50 percent below 2005 levels by 2030. Scientists say all major economies would have to cut their emissions deeply this decade to keep global warming at relatively low levels. Since 2005, United States emissions have fallen roughly 20 percent, a significant drop at a time when the economy has also expanded. But to meet its climate goals, U.S. emissions would need to decline nearly 10 times as fast each year as they’ve fallen over the past decade. That seems increasingly unlikely, experts say, especially since President-elect Donald J. Trump has promised to dismantle Mr. Biden’s climate policies and promote the production of fossil fuels, the burning of which generates greenhouse gases. “On the one hand, it is notable that we’ve now seen two years in a row where the U.S. economy grew but emissions went down,” said Ben King, an associate director at the Rhodium Group. “But it’s far from enough to achieve our climate targets.” The biggest reason that U.S. emissions have fallen in recent years is that electric utilities have been retiring their older, dirtier coal-fired power plants and replacing them with cheaper and less-polluting natural gas, wind and solar power. That trend mostly continued last year, with a few unexpected ups and downs. The nation’s demand for electricity, which has stayed more or less flat for two decades, suddenly jumped by roughly 3 percent in 2024, in large part because scorching heat during the summer caused many Americans to crank up their air-conditioners. A smaller factor was that tech companies have been building more energy-hungry data centers in states like Virginia and Texas. While power companies installed large numbers of wind turbines, solar panels and batteries last year to meet rising demand, natural gas use also rose to record highs, while coal use declined only slightly. The net result was that emissions from the power sector increased an estimated 0.2 percent, according to the Rhodium Group. In the future, rising electricity demand could pose a major challenge to American efforts to cut emissions. As interest in artificial intelligence grows, tech companies like Amazon, Google, Meta and Microsoft are building massive data centers that require enormous amounts of power. Over the next few years, many utilities are planning to meet this demand, at least in part, by delaying retirements of existing coal plants or burning more natural gas. At the same time, transportation, the nation’s largest source of greenhouse gases, saw an 0.8 percent rise in emissions last year. Gasoline and jet fuel consumption both increased as Americans continued to drive and fly more after the pandemic. Nearly 10 percent of new car sales in 2024 were less-polluting electric vehicles, but those models still make up a small fraction of total cars on the road and have yet to put a major dent in transportation emissions. On the flip side, emissions from America’s industrial sector — which includes steel, cement and chemicals — fell by 1.8 percent in 2024. Some of that may have been the result of lost output, as two hurricanes and a strike at the nation’s ports disrupted some factory activity in the fall, Mr. King said. “It’s a reminder that there’s always some bumpiness in emissions,” Mr. King said. “It’s not just a question of how many electric vehicles are on the road or how much solar we’ve installed. A big portion of our economy still relies on fossil fuels.” One of the most striking findings in this year’s data was that emissions from oil and gas operations dropped roughly 3.7 percent in 2024. Even though the United States produced record amounts of oil and near-record amounts of natural gas last year, many companies appear to have curbed leaks of methane, which is the main ingredient in natural gas and which can seep into the atmosphere and contribute significantly to global warming. Over the past few years, the Biden administration and several states have adopted new regulations that require oil and gas producers to detect and fix methane leaks. Many companies also have financial incentives to capture methane to sell rather than vent it into the air. Between 2014 and 2024, U.S. companies appear to have reduced the amount of methane that escaped, per each cubic feet of gas they produced, by 40 percent, according to the Rhodium Group. Several experts have estimated that greenhouse gases generated in the United States could start dropping sharply in the years ahead if many clean energy policies stay in place, particularly the 2022 Inflation Reduction Act that pumped hundreds of billions of dollars into low-carbon energy technologies such as electric vehicles, wind turbines, solar panels, nuclear reactors, green hydrogen and batteries. While Mr. Trump has pledged to scrap many of Mr. Biden’s subsidies and tax credits for electric vehicles and low-carbon energy, it remains to be seen whether Congress will agree. That law has not yet had a major impact on the country’s emissions, said Mr. King, since it takes time for new factories to open and power plants to get built. But, he said, data shows that low-carbon energy and transportation now make up fully 5 percent of total U.S. private investment. “That’s a leading indicator that things are changing quickly,” he said.

Night fell as the two scientists got to work, unfurling long nets off the end of their boat. The jungle struck up its evening symphony: the sweet chittering of insects, the distant bellowing of monkeys, the occasional screech of a kite. Crocodiles lounged in the shallows, their eyes glinting when headlamps were shined their way. Across the water, cargo ships made dark shapes as they slid between the seas. The Panama Canal has for more than a century connected far-flung peoples and economies, making it an essential artery for global trade — and, in recent weeks, a target of President-elect Donald J. Trump’s expansionist designs. But of late the canal has been linking something else, too: the immense ecosystems of the Atlantic and the Pacific. The two oceans have been separated for some three million years, ever since the isthmus of Panama rose out of the water and split them. The canal cut a path through the continent, yet for decades only a handful of marine fish species managed to migrate through the waterway and the freshwater reservoir, Lake Gatún, that feeds its locks. Then, in 2016, Panama expanded the canal to allow supersize ships, and all that started to change. In less than a decade, fish from both oceans — snooks, jacks, snappers and more — have almost entirely displaced the freshwater species that were in the canal system before, scientists with the Smithsonian Tropical Research Institute in Panama have found. Fishermen around Lake Gatún who rely on those species, chiefly peacock bass and tilapia, say their catches are growing scarce. Researchers now worry that more fish could start making their way through from one ocean to the other. And no potential invader causes more concern than the venomous, candy-striped lionfish. They are known to inhabit Panama’s Caribbean coast, but not the eastern Pacific. If they made it there through the canal, they could ravage the defenseless local fish, just as they’ve done in the Gulf of Mexico and the Caribbean. Already, marine species are more than occasional visitors in Lake Gatún, said Phillip Sanchez, a fisheries ecologist with the Smithsonian. They’re “becoming the dominant community,” he said. They’re “pushing everything else out.” On a recent evening, Dr. Sanchez and a Smithsonian biologist, Víctor Bravo, brought seven nets on the lake. Each one was at least 150 feet long and 10 feet wide, with meshes of varying sizes to snare fish by the gills. The scientists set the nets at different spots then stayed on their boat overnight to make sure the crocodiles didn’t eat their catch. Later, they and other researchers would analyze the captured fish in the lab to figure out where they had swum in from and how they fit into the lake’s food web. Mr. Bravo tied one end of a net to a tree branch. “Vamos!” he called out. The captain threw the boat into reverse, pulling the net taut. Then, they waited. The Panama Canal has a long history of sea creatures voyaging through as stowaways on ships’ hulls and in their ballast tanks: oysters from the Indo-Pacific, jellyfish from the Black Sea, worms from mud flats in the Netherlands. As far as scientists can tell, however, the latest watery trespassers aren’t arriving by boat. As part of the canal’s recent expansion, Panama added a new lane at each entrance, with new locks that can raise and lower today’s king-size cargo ships. Naturally, the new locks are bigger than the old ones. So each time a vessel passes through, more fresh water spills out to the ocean and more seawater sloshes in — and with it, perhaps, more coastal fish. All that extra seawater washing in has also made parts of the lake saltier. So far, though, the increase in salinity hasn’t been big enough to account for the sudden presence of so many marine fish, said Gustavo Castellanos-Galindo, a postdoctoral fellow at the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Berlin, who studies the canal ecosystem. Instead, he and other scientists reckon it’s the combined effect of bigger locks, bigger ships and bigger water volumes that has allowed more fish to swim or drift into the canal. “There’s just more opportunity for them to move in,” said Diana Sharpe, a freshwater ecologist at Harvard. The fishermen of Gatún, who know the lake better than anyone, say the effects have been sweeping. From his home in Cuipo, a village of rainbow-colored houses on the lake’s western shore, Félix Martínez González has for decades prowled the waters on a powder blue canoe. On a recent day, he harpooned 16 pounds of fish in six hours. Before the canal was expanded, he would have caught twice as much, he said. Advertisement SKIP ADVERTISEMENT He blames the salt. Rising salinity might be killing off the vegetation where the tilapia and peacock bass like to live. (Another possible factor, Dr. Sharpe said, is that the lake’s fish now have to compete against the marine invaders for food.) Over coffee on his porch, Mr. Martínez González, who is in his mid-60s, takes the long view. “I’m not worried for myself; I’m worried for the next generation,” he said. “All this affects them, too.” The canal’s peacock bass are also a popular game fish. But with the population under strain, Oswaldo Alberto Robles, 54, a fishing guide, wonders whether it makes sense for tournaments to keep giving prizes for them. “Imagine 20, 30, 40 boats searching for one fish,” he said. “We’ll just keep running out of them even faster.” The fish problem is hardly the only headache the canal expansion has created for Panama. Saltwater intrusion is threatening Lake Gatún’s other main function — namely, providing drinking water for half the country’s people. The canal authority is examining ways to desalinate portions of the lake. It is also planning to dam another river to create a new freshwater reservoir, and in the process displace 2,000 or so people, most of them poor. To critics, the situation suggests a lack of foresight by the Panamanian authorities: The costly, disruptive canal expansion created problems that only another costly, disruptive project can fix. “The truth is, before the expansion, the problem of salinity in the lake wasn’t discussed,” said Manuel Cheng Peñalba, a member of Panama’s legislature and former officer for the canal. Now, he said, Panamanians are worrying about drinking water despite living in one of the rainiest countries on Earth. When asked whether the canal should have been expanded without first securing a new water supply, Ricaurte Vásquez Morales, the canal administrator, emphasized how vital the expansion had been for Panama. Ships were outgrowing the canal’s original locks. The nation had a choice: keep up or “lag behind,” he said. Juan Carlos Navarro, Panama’s environment minister, used a Spanish expression to describe how the government would resolve the canal’s environmental issues: “I get dressed slowly because I’m in a hurry.” In other words, urgently, but with care. “We will not get the canal wrong,” Mr. Navarro said. “Panama is the canal, and the canal is Panama.” When it comes to the fish, however, it’s not exactly clear what getting it right would entail. Adding more fresh water wouldn’t necessarily stop invaders from swimming through the new locks. Putting up electric barriers or curtains of air bubbles might keep some species out but not others. Barriers might also impede ship traffic. With many invasive species, you can’t predict whether they’ll live quietly in their new homes or “blow up,” said Bella Galil, the curator emerita of crustaceans at the Steinhardt Museum of Natural History in Tel Aviv. Advertisement SKIP ADVERTISEMENT Dr. Galil has for decades studied invasions of non-native species that traveled through the Suez Canal, including jellyfish, mussels, puffer fish, rabbit fish — hundreds of them in all. The jellyfish weren’t known to congregate en masse in their old home in the Red Sea, she said. Yet in the Mediterranean they gather in swarms, stinging children on the beach, clogging fishermen’s nets and plastering the intakes of desalination plants with their sticky bodies. Regulators have occasionally gotten serious about controlling such intruders, Dr. Galil said. Even then, success is neither cheap nor quick nor assured. “It takes a lifetime,” she said. But “if you don’t start, you are left with a destroyed sea.” Back on the scientists’ boat in Lake Gatún, it was almost midnight: time for Mr. Bravo and Dr. Sanchez to check their nets. They roused themselves and began retracing their path across the dark water. At their first stop, they each grabbed one side of the net and pulled it aboard. The night’s first catch was a sea catfish from the Pacific. The second: a snook, another coastal species. When the scientists reached the end of the net, they lifted it and shook. Tiny anchovies and silversides rained onto the deck. “These are marine species, too,” Mr. Bravo said. “Now these little fish are found throughout the lake.” He slipped the silvery bodies into a Ziploc bag, which he labeled and tossed into a cooler. The other nets held similarly mixed-up smorgasbords of species and origins: one snook from the Caribbean and another from the Pacific. A slender, elegant ladyfish and a long-nosed needlefish, both Caribbean. More stubby forage fish, some native, others not. Smithsonian researchers have been sampling the fish of Gatún this way for more than a decade. They examine the fishes’ eye lenses, their muscle tissue and the contents of their stomach. Dr. Sanchez is analyzing their otoliths, the calcified structures in their inner ear that, like tree rings, record vivid histories of their surroundings. At sunrise, he and Mr. Bravo hauled up their nets a second time. Dawn’s light was gentle and rosy. The scientists’ boat looked toylike next to the tankers making morning crossings through the canal. Mr. Bravo pondered the changing lake and the communities that live off it. Advertisement SKIP ADVERTISEMENT “You feel a little sad,” he said, “because many people who have dedicated themselves to fishing for subsistence, for food, who have no other kind of work — they have to fish.” But some of the new trespassers, like jacks, are harder to catch than the species they’re replacing. The new fish are faster, more aggressive — less “stupid,” Mr. Bravo said. Even now, Gatún might not be done changing. All the jumbling of species could lead some of them to crossbreed, scientists say — with effects on the lake, and the two vast oceans beyond, that are very hard to predict.

Roughly 2,000 years ago, the Roman Empire was flourishing. But something sinister was in the air. Literally. Widespread pollution in the form of airborne lead was taking a toll on health and intelligence, researchers reported on Monday in the journal Proceedings of the National Academy of Sciences. During the roughly two centuries starting in 27 B.C., a period of relative stability and prosperity known as the Pax Romana, the empire extended throughout Europe, the Middle East and North Africa. Its economy relied on silver coinage, which required huge mining operations. But extracting silver from the Earth creates a whole lot of lead, said Joseph McConnell, an environmental scientist at the Desert Research Institute, a nonprofit group based in Nevada, and the lead author of the new research. “If you produce an ounce of silver, you’d have produced something like 10,000 ounces of lead.” Advertisement SKIP ADVERTISEMENT And lead has a host of negative effects on the human body. “There is no such thing as any safe level of lead exposure,” said Deborah Cory-Slechta, a neurotoxicologist at the University of Rochester Medical Center who was not involved in the research. Dr. McConnell and his colleagues have now detected lead in layers of ice collected in Russia and Greenland that date to the time of the Roman Empire. Lead entered the atmosphere from Roman mining operations, hitched a ride on air currents and eventually fell out of the atmosphere as snow in the Arctic, the team surmised. The levels of lead that Dr. McConnell and his collaborators measured were extremely low, roughly one lead-containing molecule per trillion molecules of water. But the ice samples were collected thousands of miles from southern Europe, and lead concentrations would have been highly dispersed after such a long journey. In order to estimate the amount of lead originally emitted by Roman mining operations, the researchers worked backward: Using powerful computer models of the planet’s atmosphere and making assumptions about the location of the mining sites, the team varied the amount of lead emitted to match the concentrations they measured in the ice. In one case, they assumed that all silver production took place at a historically important mining site in southwestern Spain known as Rio Tinto. In another case, they presumed that silver mining was equally spread out across dozens of sites. Advertisement SKIP ADVERTISEMENT The team calculated that anywhere from 3,300 to 4,600 tons of lead were being emitted into the atmosphere each year by Roman silver-mining operations. The researchers then estimated how all that lead would be scattered across the Roman Empire. “We ran the model in the forward direction to see how those emissions would be distributed,” Dr. McConnell said. With those atmospheric-lead concentrations in hand, the researchers next used modern-day data to estimate how much lead would have entered the bloodstreams of people in ancient Rome. Dr. McConnell and his colleagues focused on infants and children. Young people are particularly susceptible to taking up lead from their environment via ingestion and inhalation, said Dr. Bruce Lanphear, a public heath physician at Simon Fraser University in British Columbia who was not involved in the research. “Pound for pound, children, particularly infants, eat more and breathe more.” In recent decades, lead levels in children’s blood have been correlated with a slew of physical and mental health metrics, including I.Q., Dr. Cory-Slechta said. “We have actual data on I.Q. scores in kids with different blood-lead concentrations.” Using those modern-day relationships, Dr. McConnell and his team estimated that children across much of the Roman Empire would have had around 2 to 5 additional micrograms of lead, per deciliter of blood. Such levels correspond to I.Q. declines of roughly 2 or 3 points. For comparison, American children in the 1970s had average blood-lead-level enhancements of around 15 micrograms more lead per deciliter of blood before the phasing out of leaded gasoline and leaded paints. Their corresponding average I.Q. decline was about 9 points. But lead exposure would have had other negative effects on Romans as well. Higher levels of lead in the blood have also been linked to higher incidences of preterm births and reduced cognitive functioning in old age. “It follows you throughout life,” Dr. Lanphear said. Some scholars have hypothesized that lead poisoning played an important role in the decline of the Roman Empire. But that idea has been called into question, at least when it comes to water contaminated by lead pipes. A 2014 study showed that, while the pipes used to distribute water in Rome increased lead levels, the water was unlikely to be truly harmful. These new findings make sense, said Hugo Delile, a geoarchaeologist at the French National Centre for Scientific Research, who was not involved in the research. “They confirm the extent of lead pollution resulting from Roman mining and metallurgical activities.” According to Dr. McConnell, the research also confers a dubious honor on Roman mining. “To my knowledge, it’s the earliest example of widespread industrial pollution,” he said.

The Biden administration on Friday made final its long-awaited plan to offer billions of dollars in tax credits to companies that make hydrogen, in the hopes of building up a new industry that might help fight climate change. When burned, hydrogen mainly emits water vapor, and it could be used instead of fossil fuels to make steel or fertilizer or to power large trucks or ships. But whether or not hydrogen is good for the climate depends on how it is made. Today, most hydrogen is produced from natural gas in a process that emits a lot of planet-warming carbon dioxide. The Biden administration wants to encourage companies to make so-called clean hydrogen by using wind, solar or other low-emission sources of electricity. In 2022, Congress approved a lucrative tax credit for companies that make clean hydrogen. But the Treasury Department needed to issue rules to clarify what, exactly, companies had to do to claim that credit. The agency released proposed guidance in 2023 but many businesses have been waiting for the final rules before making investments. Advertisement SKIP ADVERTISEMENT The final guidelines that were released Friday followed months of intense lobbying from lawmakers, industry representatives and environmental groups and roughly 30,000 public comments. They include changes that make it somewhat easier for hydrogen producers to claim the tax credits, which could total tens of billions of dollars over the next decade. “Clean hydrogen can play a critical role decarbonizing multiple sectors across our economy, from industry to transportation, from energy storage to much more,” said David Turk, the deputy secretary of energy. “The final rules announced today set us on a path to accelerate deployment.” Initially, Treasury had imposed strict conditions on hydrogen subsidies: Companies could claim the tax credit if they used low-carbon electricity from newly built sources like wind or solar power to run a machine called an electrolyzer that can split water into hydrogen and oxygen. Starting in 2028, those electrolyzers would have to run during the same hours that the wind or solar farms were operating. Without those conditions, researchers had warned, electrolyzers might draw vast amounts of power from existing electric grids and drive a spike in greenhouse gas emissions if coal- or gas-fired power plants had to run more often to meet the demand. Yet many industry groups and lawmakers in Congress complained that the proposed rules were so stringent, they could throttle America’s nascent hydrogen industry before it even got going. Among the concerns: The technology to match hydrogen production with hourly fluctuations in wind and solar power is still in its infancy. Owners of nuclear reactors also said that they had been left out. So the final rules contain several significant tweaks: Hydrogen producers will get two extra years — until 2030 — before they are required to buy clean electricity on an hourly basis to match their output. Until then, they can use a looser annual standard and still claim the tax credit. In certain states that require utilities to use more low-carbon electricity each year, hydrogen producers will now have an easier time claiming the credit, on the theory that those laws will prevent a spike in emissions. For now, Treasury said, only California and Washington meet this criterion, but other states could qualify in the future. Under certain conditions, companies that own nuclear reactors that are set to be retired for economic reasons can now claim the credit to produce hydrogen if it would help the plants stay open. Existing reactors that are profitable would not be able to claim the credit. The final rules also lay out criteria under which companies could use methane gas from landfills, farms or coal mines to produce hydrogen — if, for instance, the methane would have otherwise been emitted into the atmosphere. The guidelines “incorporate helpful feedback from companies planning investments,” said Wally Adeyemo, the deputy Treasury secretary. Some hydrogen producers said that many, though not all, of their biggest concerns had been addressed in the final guidance, which runs nearly 400 pages. “There’s a degree of relief that the rules are, on balance, an improvement from the original draft,” said Frank Wolak, chief executive of the Fuel Cell and Hydrogen Energy Association, a trade group. “But there’s a lot in the details that needs to be evaluated.” The lack of clear guidance had been holding up investment, said Jacob Susman, chief executive of Ambient Fuels, a clean hydrogen developer that is planning roughly $3 billion in projects across the United States. “Now that we actually have something solid, we can get down to the business of building,” he said. Environmentalists said that most of the safeguards in the original proposal to prevent emissions from surging had been kept in place. “The extra flexibilities granted to the green hydrogen industry are not perfect from a climate perspective,” said Erik Kamrath at the Natural Resources Defense Council. “But the rule maintains key protections that minimize dangerous air and climate pollution from electrolytic hydrogen production.” The Energy Department estimates that the use of cleaner forms of hydrogen could grow to 10 million tons per year by 2030, up from virtually nothing today. But political uncertainty looms. A new Congress could repeal the tax credits, although hydrogen generally enjoys support from both Democrats and Republicans and a number of oil and gas companies have invested in hydrogen technologies. The Trump administration could also revise the rules around the credits, although that could take years. Economics are another hurdle. Producing cleaner hydrogen still costs $3 to $11 per kilogram, according to data from BloombergNEF. By contrast, it costs about $1 to $2 per kilogram to make hydrogen from natural gas. The new tax credit will be worth up to $3 per kilogram, which could bridge the gap in some cases but not all. Technology costs would have to decline sharply. Even with hefty subsidies to produce hydrogen, it’s not clear that enough buyers will emerge. Around the world, hydrogen companies have canceled several major projects over the last few years because of lack of demand. Steel makers and electric utilities that might have interest in the fuel often balk at the costly equipment required to use it. “These new rules will probably help, even if they don’t go as far as many in industry wanted,” said Aaron Bergman, a fellow at Resources for the Future, a nonpartisan Washington research organization. “But there’s still the challenge of finding the people to consume the hydrogen you produce.”

It was a novel idea at the time, but one that made sense: In 1979, President Jimmy Carter had 32 solar panels installed on the roof of the White House. They were removed just seven years later, under President Ronald Reagan. But that wasn’t the end of their story. They were picked up at a bargain price by a small college in Maine, where they continued to generate power for years, and eventually ended up scattered around the United States and China. When the panels were first set up on the roof of the West Wing, energy independence was a big issue in America. An oil embargo imposed by Arab countries in 1973, in part to pressure the United States over its support for Israel in a brief war that year, had sent shock waves though the American economy. “This dependence on foreign sources of oil is of great concern to all of us,” Mr. Carter said at an event to introduce the solar array. “No one can ever embargo the sun or interrupt its delivery to us.” Advertisement SKIP ADVERTISEMENT It was a decade before the first congressional hearing on climate change. “There’s no doubt Jimmy Carter was well ahead of his time,” said Ernest Moniz, the energy secretary under President Barack Obama and now chief executive of Energy Futures Initiative, a nonprofit group focused on renewable energy. In 1986, the Reagan administration had the panels removed during work on the White House roof. They were never reinstalled. The rejected panels, which had been used to heat water in the White House, were shipped to the suburbs of Washington, where they languished in a Virginia warehouse for years. Then, in 1991, Peter Marbach, a director at Unity College in Maine, was trying to figure out how to dig the school out of a financial hole. He spotted a picture of the panels in a magazine and decided he wanted to bring them back to life. “It was a combination of utter disbelief and anger that Reagan had taken them down, and a simultaneous crazy ‘lightbulb’ idea to get the panels and draw attention to Unity’s mission as an environmental college,” said Mr. Marbach, who is now a landscape photographer based in Oregon. He wrote a letter to Mr. Carter to ask for his blessing. The former president promptly responded with a handwritten note saying it would please him very much to see the panels put to use again.Within six weeks, Mr. Marbach had removed the seats from a blue bus used by Unity’s soccer team and driven down to Virginia. He rode a golf cart through a building that reminded him of the warehouse scene in “Raiders of the Lost Ark.” He found the panels piled haphazardly in a corner among a jumble of crates and surplus furniture. Some were broken. But Mr. Marbach loaded all the ostracized panels into the bus and brought them home to Maine. Unity College paid the United States government an administrative fee of $500 for the panels, which cost about $28,000 when first installed. Half ended up on the roof of the Unity College cafeteria, heating water. The other half, which didn’t fit on the building, were stored in a former chicken barn and used for spare parts. While acquiring the panels was “more symbolic,” Mr. Marbach said, they did help the college save money. They remained in place until 2010, after they’d reached their end of lives. Advertisement SKIP ADVERTISEMENT Since then, at least six have continued on their journey beyond Maine. In 2007, one to two panels were driven in the back of a pickup truck from Unity College down to the Carter Library in Atlanta by a team of documentarians making a film on Mr. Carter’s solar legacy called “A Road Not Taken.” In 2009, another was donated to the National Museum of American History in Washington. A Smithsonian spokeswoman said that panel remains on display today. The Solar Science and Technology Museum in Dezhou, China, acquired another panel in 2010. In the same year, another was donated to the Solar Energy Industries Association. Others are held by NRG Systems, Inc., a clean energy manufacturer in Vermont, by the U.S. Department of Energy, with the rest still held by Unity College, which has changed its name to Unity Environmental University. Mr. Carter seemed to know that the transition to clean energy would face obstacles. “A generation from now, this solar heater can either be a curiosity, a museum piece, an example of a road not taken or it can be just a small part of one of the greatest and most exciting adventures ever undertaken by the American people,” he said in 1979. But even though the panels didn’t last long at the White House, Mr. Carter’s decision to support renewable energy helped position the United States for the clean power boom currently underway, experts said. “It was fundamental to the development and the growth of the use of solar energy in the U.S.,” said Frederick Morse, a senior Energy Department official under Mr. Carter and Mr. Reagan and now chief executive of SolStor Energy, a solar development company.

It kills more people each year than car crashes, war or drugs do. This invisible killer is the air pollution from sources like cars and trucks or factory smokestacks. But as wildfires intensify and grow more frequent in a warming world, the smoke from these fires is emerging as a new and deadly pollution source, health experts say. By some estimates, wildfire smoke — which contains a mixture of hazardous air pollutants like particulate matter, nitrogen dioxide, ozone and lead — already causes as many as 675,000 premature deaths a year worldwide, as well as a range of respiratory, heart and other diseases. Research shows that wildfire smoke is starting to erode the world’s progress in cleaning up pollution from tailpipes and smokestacks, as climate change supercharges fires. “It’s heartbreaking, it really is,” said Dr. Afif El-Hasan, a pediatrician who specializes in asthma care at Kaiser Permanente in Southern California and a board director of the American Lung Association. Wildfires “are putting our homes in danger, but they’re also putting our health in danger,” Dr. El-Hasan said, “and it’s only going to get worse.” Advertisement SKIP ADVERTISEMENT Those health concerns were coming to the fore this week as wildfires ravaged the Los Angeles area. Residents began to return to their neighborhoods, many strewed with smoldering ash and rubble, to survey the damage. Air pollution levels remained high in many parts of the city, including in northwest coastal Los Angeles, where the air quality index climbed to “dangerous” levels. Los Angeles, in particular, has seen air pollution at levels that could be raising daily mortality by between 5 to 15 percent, said Carlos F. Gould, an expert in the health effects of air pollution at the University of California, San Diego. That means current death counts, “while tragic, are likely large underestimates,” he said. People with underlying health issues, as well as older people and children, are particularly vulnerable. The rapid spread of this week’s fires into dense neighborhoods, where they burned homes, furniture, cars, electronics and materials like paint and plastic, made the smoke more dangerous, said Dr. Lisa Patel, a pediatrician in the San Francisco Bay Area and the executive director of the Medical Society Consortium on Climate and Health. Advertisement SKIP ADVERTISEMENT A recent study found that even for homes that are spared destruction, smoke and ash blown inside could adhere to rugs, sofas and drywall, creating health hazards that can linger for months. “We’re breathing in this toxic brew of volatile organic compounds and polycyclic aromatic hydrocarbons and hexavalent chromium,” Dr. Patel said. “All of it is noxious.” Intensifying and more frequent fires, meanwhile, are upending experts’ understanding of smoke’s health effects. “Wildfire season is no longer a season,” said Colleen Reid, who researches the effects of air pollution from wildfires on health at the University of Colorado Boulder. “We have fires all year round that affect the same population repeatedly.” “The health impacts are not the same as if you were exposed once, and then not again for 10 years,” she said. “The effects of that is something that we still don’t really know.” A United Nations report from 2022 concluded that the risk of devastating wildfires around the world would surge in coming decades. Heating and drying caused by climate change, along with development in places vulnerable to fire, was expected to intensify a “global wildfire crisis,” the report said. Both the frequency and intensity of extreme wildfires have more than doubled in the past two decades. In the United States, the average acreage burned a year has surged since the 1990s. Now, pollution from wildfires is reversing what had been a decades-long improvement in air quality brought about by cleaner cars and power generation. Since at least 2016, in nearly three-quarters of states in the U.S. mainland, wildfire smoke has eroded about 25 percent of progress in reducing concentrations of a type of particulate matter called PM 2.5, a Nature study in 2023 found. In California, wildfire smoke’s effect on air quality is offsetting public health gains brought about by a decline in air pollution from automobiles and factories, state health officials have found. (By releasing carbon dioxide and other planet-warming gases into the atmosphere, wildfires are themselves a big contributor to climate change: The wildfires that ravaged Canada’s boreal forests in 2023 produced more greenhouse gases than the burning of fossil fuels in all but three countries.) ”It’s not a pretty picture,” said Dr. Gould of U.C. San Diego, who took part in the Nature study. If planet-warming gas emissions continue at current levels, “we’ve got some work that suggests that mortality from wildfire smoke in the U.S. could go up by 50 percent,” he said. One silver lining is that the Santa Ana winds that so ferociously fueled the flames in recent days have been blowing some of the smoke toward the ocean. That stands in contrast to the smoke from the 2023 Canadian wildfires that drifted to New York and other American states hundreds of miles away, causing spikes in emergency room visits for asthma. At one point that year, more than a third of Americans, from the East Coast to the Midwest, were under air quality alerts from Canadian wildfire smoke. “We’re seeing new and worsening threats in places that are not used to them,” Dr. Patel, the pediatrician, said. Advertisement SKIP ADVERTISEMENT The new normal is bringing about changes to health care, Dr. Patel said. More health systems are sending out air quality alerts to vulnerable patients. In the small community hospital where she works, “every child that comes in with wheezing or asthma, I talk to them about how air pollution is getting worse because of wildfires and climate change,” she said. “I teach them how to look up air quality, and say they should ask for an air purifier,” Dr. Patel added. She also cautions that children should not participate in cleanup after a wildfire. Scientists are still trying to understand the full range of wildfire smoke’s health effects. One big question is how much of what researchers know about vehicle exhaust and other forms of air pollution apply to wildfire smoke, said Mark R. Miller, a researcher at the Center for Cardiovascular Science at the University of Edinburgh who led a recent global survey of climate change, air pollution and wildfires. For example, exhaust particles “are so small that when we breathe them in, they go deep down into our lungs and are actually small enough that they can pass from our lungs into our blood,” he said. “And once they’re in our blood, they can be carried around our body and start to build up.” That means air pollution affects our entire body, he said. “It has effects on people who have diabetes, has effects on the liver and the kidney, it has effects on the brain, on pregnancy,” he said. What’s still not clear is whether pollution from wildfires has all of those same effects. “But it’s likely,” he said. Advertisement SKIP ADVERTISEMENT Experts have a range of advice for people living in areas with smoke. Keep an eye on air quality alerts, and follow evacuation orders. Stay indoors as much as possible, and use air purifiers. When venturing outside, wear N95 masks. Don’t do strenuous exercise in bad air. Keep children, older people and other vulnerable groups away from the worst smoke. Ultimately, tackling climate change and cutting back on all kinds of air pollution is the way to reduce the overall burden on health, said Dr. El-Hasan of the American Lung Association. “Can you imagine how much worse things would be if we hadn’t started cleaning up emissions from our cars?” he said. “I’m trying to think, glass half full, but it does break my heart and it does worry me.” A correction was made on Jan. 11, 2025: An earlier version of this article stated incorrectly the surname of an expert in the health effects of air pollution at the University of California, San Diego. He is Carlos F. Gould, not Gold.