Follow live updates on President Trump’s tariffs and the global fallout.

Beijing responded swiftly on Tuesday to the tariffs President Trump had promised, announcing a fusillade of countermeasures targeting American companies and imports of critical products.

Mr. Trump’s 10 percent tariff on all Chinese products went into effect at 12:01 a.m. Tuesday, the result of an executive order issued over the weekend aimed at pressuring Beijing to crack down on fentanyl shipments into the United States.

The Chinese government came back with a series of retaliatory steps, including additional tariffs on liquefied natural gas, coal, farm machinery and other products from the United States. It also said it had implemented restrictions on the export of certain critical minerals, many of which are used in the production of high-tech products.

In addition, Chinese market regulators said they had launched an antimonopoly investigation into Google. Google is blocked from China’s internet, but the move may disrupt the company’s dealings with Chinese companies.

The U.S. tariffs, which Mr. Trump said on Monday were an “opening salvo,” come on top of levies that the president imposed during his first term. Many Chinese products already faced a 10 or 25 percent tariff, and the move adds a 10 percent tariff to more than $400 billion of goods that Americans purchase from China each year.

Mr. Trump had been planning to hit America’s three largest trading partners, Canada, Mexico and China, with tariffs of varying degrees. But after days of frantic negotiations, Mr. Trump agreed to pause the tariffs on Mexico and Canada for 30 days after the Canadian and Mexican governments promised to step up their oversight of fentanyl and the border.

On Monday, Mr. Trump said he planned to speak with the Chinese leader Xi Jinping within the next 24 hours, but it was not clear exactly when the phone call would take place. Before there was any word of a call, the Chinese authorities rolled out the measures aimed at punishing American companies.

China’s counterpunches suggested an effort to hurt American businesses and send a warning to the Trump administration, while holding in reserve measures that could do even more serious damage to trade between the world’s two biggest economies. But the measures announced by Beijing, particularly the tariffs and export controls, could take time for Chinese officials to revoke, even if Mr. Trump were to signal a willingness to compromise.

“As far as I can see so far, it’s a relatively limited response, affecting no more than 30 percent of U.S. exports to China,” said Bert Hofman, a former World Bank official and now an adjunct professor at the East Asian Institute at the National University of Singapore. “They’re probably trying to keep their powder dry, because this could still be only the first step from the Trump administration.”

The Trump administration’s tariffs “seriously undermine the rules-based multilateral training system, damage the foundation of economic and trade cooperation between China and the United States, and disrupt the stability of global industry supply chains,” China’s Ministry of Commerce said in a statement.

The commerce ministry and China’s customs agency announced new restrictions on exports of tungsten, tellurium, molybdenum and other metals important for industry and new technologies, citing “national security and interests.”

China’s measures included an additional 10 percent tariff on crude oil, agricultural equipment, larger cars and pickup trucks, as well as an additional 15 percent tariff on coal and natural gas, the Chinese tax authorities announced.

China also said it had added two American companies to its “unreliable entities” list. One of the companies, PVH — the American retailer that owns the Calvin Klein and Tommy Hilfiger brands — had already been placed under investigation by Chinese regulators in September. China said PVH had taken “discriminatory measures” against goods from the Xinjiang region in China’s far west.

Google did not immediately respond to a request for comment on the announcement of the antitrust investigation.

While Google dominates the world in digital advertising and internet search, restrictions in China mean it cannot operate its search engine, its YouTube video platform or its app store, Google Play, in the country. Still, its operating system, Android, is used by some Chinese phone makers, including Xiaomi, Lenovo and Vivo. Regulators around the world, including ones in the United States, Canada, Europe and South Korea, have probed Google on antitrust grounds or brought related cases.

Besides imposing his new tariffs, Mr. Trump’s executive order, signed on Saturday, ended a popular workaround that many Chinese companies had used to send goods to the United States without paying the tariffs that the president imposed in 2018. The provision, known as de minimis, allowed popular e-commerce companies like Shein and Temu to send billions of dollars of products from Chinese factories directly to American consumers without tariffs.

The deals that Mr. Trump made with Canada and Mexico on Monday brought the United States back from the brink of a potentially devastating trade war with two of its closest allies. But it did not preclude the threat of similar conflicts happening later.

On Monday, Mr. Trump made clear that he would deploy tariffs liberally to get other governments to give him what he wants.

Mr. Trump has accused China of failing to do enough to stop the export of fentanyl and the chemicals that are used to make it. In the executive order he issued on Saturday, Mr. Trump said that shipments of synthetic opioids had ravaged U.S. communities, put a severe strain on the health care system and were the leading cause of death for people aged 18 to 45 in the United States.

It’s not clear what steps the Chinese government has recently taken, if any, to restrict the fentanyl trade, beyond its previous law enforcement collaboration with the United States. Mr. Trump discussed fentanyl with Mr. Xi in a phone call during his first week in office.

During Mr. Trump’s first term, China introduced a ban on fentanyl and began working with the United States to catch traffickers, under pressure from Mr. Trump. And in 2023, Mr. Xi and then-President Joseph R. Biden Jr. agreed to a series of bilateral talks on narcotics after they met in Woodside, Calif.

A spokesman for the Chinese Embassy in Washington had said that China firmly opposed tariffs and that any differences or frictions should be resolved through dialogue. “There is no winner in a trade war or tariff war, which serves the interests of neither side nor the world,” the spokesman said.

Mr. Trump waged an intense trade war with China during his first term, after initiating a trade case that found that the country had unfairly infringed on U.S. intellectual property. He ratcheted up tariffs on China and ultimately applied tariffs to about 60 percent of the country’s exports to the United States.

Now Mr. Trump, in office for two weeks, has initiated a new exchange with China.

“This is likely only the beginning of a long process for the two countries to negotiate,” Zhiwei Zhang, the president and chief economist of Pinpoint Asset Management, an investment firm in Hong Kong, said in written comments. “There is hope to de-escalate in this process, though the road ahead may be bumpy.”

Claire Fu contributed reporting from Seoul, Amy Chang Chien from Taipei, Taiwan, and Nico Grant from San Francisco.

An international panel of 14 neonatal and pediatric specialists on Tuesday raised grave doubts about the evidence used to convict the British nurse Lucy Letby, who was found guilty in 2023 of murdering seven babies at the hospital where she worked.

In a dramatic news conference in London, the chair of the panel, Dr. Shoo Lee, a Canadian neonatologist, said that the extensive independent review he chaired had found no evidence that Ms. Letby had murdered or attempted to murder any of the babies in her care.

He also highlighted damning findings pointing to serious errors in medical care at the unit where the deaths occurred and to chronic failings in the management of neonatal conditions. He said that some of the deaths had been preventable.

“Our conclusion was there was no medical evidence to support malfeasance causing injury in any of the 17 cases in the trial,” Dr. Lee said. “In summary, ladies and gentlemen, we did not find any murders.”

The review is significant because it was carried out by some of the most prestigious and respected neonatal and pediatric specialists in the world.

The experts were allowed to assess all of the available medical records related to the babies, and they delivered their assessment pro bono. The panel underlined the serious pre-existing conditions of some of the babies, and in several cases, the specialists found significant errors in the treatment or care of the infants.

Ms. Letby, 35, was sentenced to a whole life order in 2023 — meaning that she would spend the rest of her life in prison — after being convicted of killing seven babies and attempting to murder seven others at the neonatal unit of the Countess of Chester Hospital in northwestern England in 2015 and 2016. She has always maintained her innocence.

The case horrified Britain, but since her convictions, dozens of experts in neonatology and statistics have raised questions about the evidence and argued that there might have been a miscarriage of justice.

Dr. Lee led the independent review of the babies’ cases, which involved a panel of specialists from countries including Britain, Canada, Germany, Japan, Sweden and the United States.

He emphasized the independence of the panel, noting that when the experts embarked on their investigation, they were clear that the report would be released whether the findings were favorable or unfavorable for Ms. Letby.

They simply focused on coming up with an “impartial cause of death based on evidence,” he said.

The review found that all the babies had died or been harmed either because of natural causes or because of errors in medical care.

Dr. Lee had coauthored an academic paper published in 1989 that looked into air embolisms in the bloodstreams of babies and noted that some showed signs of skin discoloration. That research was heavily relied on by Dr. Dewi Evans, the prosecution’s lead expert witness in the Letby case. Dr. Evans argued in court that some of the babies who died or deteriorated had exhibited similar patterns on their skin.

After the trial, Dr. Lee discovered that his research had been used to convict Ms. Letby. He agreed to give evidence in Ms. Letby’s appeal, telling a hearing that Dr. Evans had misinterpreted his findings and that none of the babies in the trial should have been diagnosed with air embolism. Ultimately, the appeal court decided that his evidence would not be heard, arguing that Ms. Letby’s defense team should have called Dr. Lee in the original trial.

The panel examined the case of each baby, and, during the briefing, highlighted a few of the cases and the panel’s detailed findings.

In the case of “Baby 1,” who prosecutors alleged was killed by Ms. Letby by injecting air into the infant’s veins, the panel determined the cause of death to be thrombosis from an existing issue.

Another child, identified by the panel as “Baby 9,” who the prosecution had argued had also died after Ms. Letby injected air, was found by the experts to have “died of respiratory complications” caused by chronic lung disease, among other issues. The panel also found that the baby’s death was likely preventable and described a number of errors in treatment.

In the case of “Baby 11,” the prosecution had argued that Ms. Letby had deliberately dislodged a breathing tube. But the experts said that there was no evidence to support the claim that the tube had been dislodged. They argued instead that an initial attempt by a consultant doctor to resuscitate the baby had been “traumatic and poorly supervised,” that the wrong equipment had been used and that the doctor “didn’t understand the basics” of how the equipment for mechanical ventilation worked.

“It was just that the consultant didn’t know what he was doing,” Dr. Lee said in summarizing the case.

Dr. Neena Modi, a member of the panel and a neonatology professor at Imperial College London, said there were “very plausible reasons for these babies’ deaths.”

“There was a combination of babies being delivered in the wrong place, delayed diagnosis and inappropriate or absent treatment,” she said. “There are clearly systemic factors at play that we have identified as well as individual factors that we have identified.”

Ms. Letby lost two separate attempts last year to appeal her convictions.

In December, Ms. Letby’s lawyer, Mark McDonald, said that he would ask the Court of Appeal to review all of her convictions because Dr. Evans, the prosecution witness, had changed his mind about how three of the babies had died.

Dr. Evans has repeatedly stood by his evidence, and he told The Times of London this past weekend that he was “very concerned people are getting their facts wrong.”

The babies’ cause of death has been called into question by experts before. In December, the defense team introduced evidence from two neonatologists, Dr. Neil Aiton and Dr. Svilena Dmitrova, who specialize in the care of premature babies. Those experts concluded that two babies whom Ms. Letby had been convicted of killing had not been well and had died for “identifiable medical reasons.”

The doctors, who consulted the medical records of the babies, found that one, identified as Baby C, died after problems with the placenta at the end of pregnancy. They concluded that another, Baby O, died as a result of issues related to resuscitation.

Mr. McDonald, the lawyer, said on Tuesday that he had applied to the Criminal Cases Review Commission, which is responsible for investigating claims of miscarriages of justice. He also noted that he had shared the evidence with Ms. Letby, and, while he declined to share further details of her state of mind, he said, “She has hope, and that’s all I can say.”

The Criminal Cases Review Commission confirmed that it had received a request to look at the case, but it was unclear how long that would take.

“We are aware that there has been a great deal of speculation and commentary surrounding Lucy Letby’s case, much of it from parties with only a partial view of the evidence,” a spokesperson for the review body said, adding that the families affected by the events should be kept in mind.

It is not for the commission to “determine innocence or guilt in a case,” the spokesperson noted, “that’s a matter for the courts.”

For about a week leading up to the A.F.C. championship game, Meredith Nolan had been living on a hulking research vessel parked in an Antarctic port. The ship, called the Noosfera, had been waiting for favorable sea conditions before plowing into the icy waters below the southern tip of South America.

It was late January, and Nolan was headed home after spending three months at Palmer Station, a tiny American research base in Antarctica.

She had been studying the effects of climate change on zooplankton, and, in her spare moments, cheering for her favorite football team, the Buffalo Bills. She wore a beanie with a Bills logo on the front and a blue poof on top when she went out on a boat to collect zooplankton in nets, or hiked the receding glacier behind the station. Her hat alerted two other Bills fans that she was one of them.

In some ways, she did not behave like a typical Bills fan, causing joyful chaos and destruction to celebrate the team.

“We’ll see if Meredith starts diving through tables,” Ricky Robbins, who was there studying seabirds, said in reference to a popular activity among fans at Bills tailgates.

But in one important way, she did.

“Every year I get excited,” Nolan said cheerfully in early November. “But I’m hopeful that this is the year.”

Since the 1950s, the National Science Foundation has funded research projects in Antarctica. Palmer Station, built in 1968, is the smallest of its three stations, housing around 40 people in the summer and about 20 in the winter. It is also the warmest, but that still means below-freezing temperatures and snow, even in the summer. Some of those there, like Nolan, are studying the effects of climate change on the environment. For many, sports are a way to stay linked with the outside world, even when connecting with their teams is a challenge.

Until recently, high-speed internet access was limited, when it was available at all. A participant manual from 2018 cautioned: “Large downloads and streaming media have a negative impact on everyone else.”

Sports fans, then, would save up their internet rations for game times.

In 2013, Ken Halanych, then a professor at Auburn University, was on a ship when Auburn won a game against its hated rival, the University of Alabama, by returning a missed field goal 109 yards for a touchdown as time expired.

Halanych spent four hours uploading a video so he could see the play.

He has been to Antarctica eight times since 2000. In 2004, when Auburn was one of three undefeated teams hoping for a spot in the national championship game, he persuaded the station manager at Palmer Station to let him raise an Auburn flag on the ship.

“I wrote ESPN trying to connect with them and saying, ‘Here’s my vote from Antarctica,’” Halanych said. “ESPN never responded.”

Darren Roberts has gone to Antarctica 13 times. He loves the work, though he recognizes that it can be isolating. Roberts isn’t sure he would still be going if his wife, Megan, weren’t part of his research team. Following the Denver Broncos helps him connect with his brother, who is 13 years older.

“It is really sweet,” Megan Roberts said. “They all really bond, especially over the Broncos, even when we’re in these crazy remote places. It’s amazing to see. He keeps in touch with his family because of what’s going on with the Broncos.”

Darren Roberts would follow Broncos games through a Google graphic that showed a little football on a digital field. Its movements corresponded to what was happening in the game.

But when the Broncos won the Super Bowl in 2016, the couple were on a research ship called the Laurence M. Gould. It was captained by a man named Ernest Stelly, a fan of the Dallas Cowboys.

Even though the Cowboys weren’t playing, Stelly pulled the vessel close enough to Palmer Station that it could use the station’s internet to pick up a radio broadcast. The cooks whipped up party snacks, and Stelly hosted a Super Bowl party.

“I remember it was great, like sitting in the dark on the ship listening to the Super Bowl on the bridge,” Roberts said. “And it was really actually very special and kind of a unique thing, especially at that time.

The United States also operates a base at the South Pole, which is much colder but slightly more populous, and an outpost called McMurdo Station, which is south of New Zealand and can support 1,500 residents.

Robbins, who is on the seabirds team with the Robertses, has worked in even more remote locales, which has made it hard for him to follow his favorite teams. He once worked on a small island in Hawaii on which just seven people, including himself, lived. Experiences like that make Antarctica feel “big city almost,” he said.

“Having, like, a galley with chefs and a bedroom and running water and freshwater showers is like, it feels very luxurious,” Robbins said.

The seabird group works out of a small building separate from other scientists. Robbins called it “the birder hut.”

“Darren’s rumor is that we used to be in the big building with an office, but everybody got really sick of smelling penguin poop,” Robbins said.

Work got busier toward the end of their stay, which meant it wasn’t as easy to follow the end of football season. All the birds’ eggs were hatching, and the team had to measure their chicks. The researchers tagged some birds, and removed tags from others, sometimes late at night or early in the morning.

They were out counting penguin colonies and measuring giant petrel chicks when the Broncos lost to the Bills in the playoffs.

Nolan was happy with the outcome of that game. Sports are a bonding point between Nolan and her father, Jim. He is extraordinarily proud that his daughter works in Antarctica, and has grown accustomed to explaining zooplankton to others.

“It’s kind of the bottom of the food chain,” he tells people. “Without zooplankton we’d all be in trouble.”

At home, Meredith lives about 30 minutes away from her parents, as a graduate student at the Virginia Institute of Marine Science. They love hearing about her work and receiving pictures of penguins via text message.

“She’s an amazing kid,” Jim said.

They text constantly during games, particularly when Jim isn’t too stressed.

In late December, when the Bills played the New York Jets, she was putting krill into bottles to begin an experiment. Jim texted to her that she shouldn’t worry, the game was a blowout. The Bills won, 40-14.

Palmer base now uses the Starlink satellite system for high-speed internet access. In mid-December the satellites began pinging from the United States rather than Chile, which meant YouTube TV was available on the base. Nolan could stream her Bills live.

Jim is a Bills fan because he grew up in upstate New York, and Meredith inherited the condition from him. He lived through decades of disappointment, including four consecutive losses in the Super Bowl. His daughter, 24, has seen less of that.

“She’s a very optimistic person, probably more optimistic than I am,” Jim said. “But sometimes, being a Bills fan, it can be tough.”

The Noosfera finally got clearance to sail away on that Sunday evening last month, minutes before the A.F.C. championship game kicked off. Jim tracked the boat on a site called MarineTraffic.com. He doesn’t worry about Meredith too much, but the Drake Passage, an expanse of sea between Palmer Station and Chile, can have 40-foot waves.

After she settled in, Nolan fired up her iPad and logged into YouTube TV. She sent a photo of the setup to her father — it showed the back of Josh Allen’s head and the score of the game, 27-10, Chiefs. She watched as the Bills attempted a comeback, then lost, 32-29, just one game short of the Super Bowl.

“It was quite a bummer,” Nolan said in a text message as the ship made its way toward the potentially treacherous Drake Passage. She added an emoji of a crying face. “But still a great season!”