John Cleese said that he decided to cut the N-word from a scene in his West End Fawlty Towers revival because in contemporary Britain there are too many “literal-minded people” who “don’t understand irony”.

Cleese was speaking at the media launch for the West End theatrical adaptation of the classic comedy, which follows a repressed hotelier trying to control his chaotic staff. The TV show finished in 1979 after two series that are widely regarded to contain some of the best-ever British sitcom writing.

The new two-hour version features scenes from three episodes of the series: The Hotel Inspector, Communication Problems, and The Germans, which originally featured a scene in which a character used racial slurs, including the N-word, while discussing a cricket match.

“Whenever you’re doing comedy you’re up against the literal-minded, and the literal-minded don’t understand irony and if you take them seriously you get rid of a lot of comedy,” Cleese said, explaining the reason for altering the script.

“They don’t understand metaphor, irony or comedy exaggeration … they’re not playing with a full deck.”

He also defended the overtly racist comedies of the 1970s, such as Till Death Do Us Part, which featured the character Alf Garnett, who was played by Warren Mitchell and was known for his racist outbursts.

“People were roaring with laughter at him, not with him, but there were also people saying: ‘Thank God these things are being said at last,’” said Cleese.

In a recent piece for the Telegraph, Cleese said that he yearned for “a return to what seemed to be a happier, friendlier, calmer, more ironic culture”, while admitting that he’d considered keeping the N-word in the adaptation but decided “it’s not worth the trouble”.

Fawlty Towers is the latest sitcom from the 1970s, 80s and 90s to make a stage transfer.

Drop the Dead Donkey: The Reawakening!, The Good Life, Some Mothers Do ’Ave ’Em, The Fast Show and Only Fools and Horses have already been adapted (Fawlty Towers is directed by Caroline Jay Ranger, who also directed Only Fools and Horses).

One critic said “a thirst for nostalgia and familiarity” was behind the trend, while another argued that audiences missed “big, unifying pop-cultural ­television events from the days before ­multiple channels, streaming and the diffuseness of ­content”.

Cleese also said there had been “too much change” in British society over recent years.

“There’s been too much change. Everyone is getting very anxious and people behave in a ratty sort of way and are more likely to become more literal-minded,” he said. “I’m not sure what you do about it, maybe uninvent the internet?”

He also believes that Britain has undergone “Americanisation” and is now too obsessed with earning money and status, while the “lower middle class” people he grew up with in Weston-super-Mare in the 1950s were more content to “do their job well …[and] live a good life”.

“One of the sad things about our culture now is that we’ve been infected by the American view that if you’re not rich or famous you’re a bit of a failure,” he added.

Cleese is also working on a TV revival of Fawlty Towers with his daughter, where Basil Fawlty will end up in the Caribbean helping his estranged daughter, who is also a hotelier. Cleese promised: “He will still be repressed and trapped.”

Fawlty Towers: The Play will open on Wednesday 15 May at London’s Apollo Theatre on Shaftesbury Avenue in the West End, and will run until 28 September.

The high intelligence levels of orangutans have long been recognised, partly due to their practical skills such as using tools to crack nuts and forage for insects. But new research suggests the primate has another handy skill in its repertoire: applying medicinal herbs.

Researchers say they have observed a male Sumatran orangutan treating an open facial wound with sap and chewed leaves from a plant known to have anti-inflammatory and pain-relieving properties.

It is not the first time wild animals have been spotted self-medicating: among other examples, Bornean orangutans have been seen rubbing their arms and legs with chewed leaves from a plant used by humans to treat sore muscles, while chimpanzees have been recorded chewing plants known to treat worm infections and applying insects to wounds.

However, the new discovery is the first time a wild animal has been observed treating open wounds with a substance known to have medicinal properties.

“In the chimpanzee case they used insects and unfortunately it was never found out whether these insects really promote wound healing. Whereas in our case, the orangutan used the plant, and this plant has known medical properties,” said Dr Caroline Schuppli, senior author of the research based at Max Planck Institute of Animal Behavior in Germany.

The team say the findings offer insight into the origins of human wound care – the treatment of which was first mentioned in a medical manuscript dating to 2200BC.

“It definitely shows that these basic cognitive capacities that you need to come up with a behaviour like this … were present at the time of our last common ancestor most likely,” said Schuppli. “So that that reaches back very, very far.”

Writing in the journal Scientific Reports, Schuppli and colleagues report how they made the discovery while working in a research area of a protected rainforest in Indonesia.

The team describe how, while tracking a male Sumatran orangutan called Rakus, they noticed he had a fresh facial wound – probably the result of a scrap with another male. Three days later, Rakus was seen feeding on the stem and leaves of Fibraurea tinctoria – a type of liana climbing vine.

Then he did something unexpected.

“Thirteen minutes after Rakus had started feeding on the liana, he began chewing the leaves without swallowing them and using his fingers to apply the plant juice from his mouth directly on to his facial wound,” the researchers write.

Not only did Rakus repeat the actions, but shortly afterwards he smeared the entire wound with the chewed leaves until it was fully covered. Five days later the facial wound was closed, while within a few weeks it had healed, leaving only a small scar.

The team say the plant used by Rakus is known to contain substances with antibacterial, anti-inflammatory, anti-fungal, antioxidant, pain-killing and anticarcinogenic properties, among other attributes, while this and related liana species are used in traditional medicine “to treat various diseases, such as dysentery, diabetes and malaria”.

It remains unclear whether Rakus figured the process out for himself or learned it from another orangutan, although it has not been seen in any other individual.

Schuppli added that Rakus appeared to have used the plant intentionally.

“It shows that he, to some extent, has the cognitive capacities that he needs to treat the wound with some medically active plants,” she said. “But we really don’t know how much he understands.”

People in Britain and Ireland are being asked to monitor their local rivers for pollution so a leading water charity can measure the scale of the sewage crisis.

The Rivers Trust is this week launching the Big River Watch, asking people to record observations of their local rivers on a free app. The results will be made available through an interactive dashboard, and will help the organisation, as well as individuals and communities who can all access the data, to take action to improve rivers.

Volunteers will be asked to identify sewage pollution, sewage fungus, minewater and silt, along with other indicators of river health, so pollution hotspots can be identified and tackled. The Rivers Trust is hoping for it to be the UK and Ireland’s biggest ever mass participation survey of river health.

Tessa Wardley, director for communications and advocacy at the trust, said: “In September 2023, 60% of Big River Watch participants were new to citizen science, which shows just how important this tool is to help everyone get involved and showing they care about rivers. As well as learning where pollution and wildlife are spotted, we also want to know how spending time near rivers affects people’s wellbeing, so I’d encourage anyone and everyone to spend some time by their river and make their voice heard.”

UK and Irish rivers have been choked by sewage pollution, as the sewer system allows untreated human waste to mix with rainwater and domestic wastewater, meaning that the pipes become overwhelmed. This toxic cocktail of sewage and chemicals is then drained into waterways to prevent it backing up into homes.

Data first revealed by the Guardian found that 2023 was a record year for sewage spills. Raw sewage was discharged for more than 3.6m hours into rivers and seas in a 105% increase on the previous 12 months.

Water industry figures have admitted that this is due to a lack of investment in pipes and sewers, and as climate breakdown brings heavier rains and the population rises, the system is failing.

Emma Brisdion, marketing campaigns lead at the Rivers Trust, said: “Healthy rivers are essential for our wellbeing and for our wildlife. But rivers in the UK and Ireland have been allowed to get into a desperate state, and there are many people who care immensely about them and want to help.

“The Big River Watch invites communities to get involved. The simple survey is all about using that connection to rivers to record the good, the bad, and the ugly so we can understand our blue spaces better and make informed decisions about how to revive them.”

On a warm morning in March, a group of researchers entered an unassuming chop suey parlor in the Sacramento suburbs for a rare field trip.

The six history enthusiasts affiliated with the University of California, Davis, had gathered at the Chicago Cafe in Woodland, California, with one goal in mind: to determine the exact age of what may be the oldest Chinese restaurant in the country.

From cabinets underneath the diner counter, they excavated box after box of ephemera that formed a time capsule of 20th century Chinese immigrant experience. Among piles of letters, menus and tax receipts lay such relics as a vintage Chinese-English pocket dictionary, a 1976 Chinese edition California driver’s handbook and black and white polaroids of a newly crowned Miss Chinatown. To the experts’ trained eyes, seemingly any detail could reveal an artifact’s age, be it the digits of phone numbers, the typefaces on menus from decades past, or the clothing and makeup captured in photographs.

Three generations of the Fong family, hailing from an impoverished region in southern China, built the Chicago Cafe into a linchpin of Woodland civic life. Current owners Paul and Nancy Fong, who began working at the restaurant a half century ago, have been serving many of the same customers for decades. Some furnishings, like a pair of private booths and a wooden walk-in refrigerator, predate the couple’s employment, as do menu staples like the pork chow mein and chicken fried steak.

“Clearly, there’s a respect for history,” Jack Chin, a professor at the UC Davis school of law who’s leading the research into the Chicago Cafe, told his team as they perused the documents.

The words “SINCE 1903” are inked on a white board behind the counter, a sight that stayed with Chin on his many visits to eat at the restaurant over the years. In a research paper published in January, he and his scholars from UC Davis verified that the diner had been in operation since at least 1910. After analyzing historical records in the Yolo county archives, including business directories, newspaper clippings and fire insurance maps, they concluded that the Chicago Cafe might have opened earlier than Pekin Noodle Parlors in Butte, Montana, which is widely recognized as the oldest existing Chinese eatery in the US.

In the early 20th century, the restaurant industry provided a legal and financial lifeline to Chinese people. The Chinese Exclusion Act of 1882, which banned Chinese immigration to the US, later exempted merchants, a privileged class that included restaurant owners and managers. The so-called “chop suey” loophole allowed families like the Fongs to open up diners and bring over their kin. At the same time, restaurants remained a target of segregation. Chinese restaurateurs weren’t legally allowed to perform manual labor, including cooking and waiting tables. Later, as the popularity of chop suey parlors took off, officials across the country passed legislation banning white women from entering or working in chop suey parlors.

Woodland’s Chinatown was not immune to the anti-Chinese fervor that swept across California, according to newspaper clips Chin’s team uncovered. A 1910 Woodland Daily Democrat editorial proclaimed that every Chinese or Japanese farmhand “drove a white man out of the orchard”. Businesses boasted of employing “white help only” in ads.

“Chinatown was thought to be blighted, slum,” Chin said. “There was clearly a sense of separation even as the restaurant provided a method of integration.”

Yong Chen, author of Chop Suey, USA: the Story of Chinese Food in America, said Chinese restaurants like Chicago Cafe endured not because Americans were enamored with Chinese food. Rather, they filled a void of “convenient and affordable” offerings missing from the gastronomical landscape, becoming a precursor of sorts to fast food chains.

“The restaurant industry in the 20th century is not an industry people wanted to get into,” Chen said. “It’s so much hard work, the pay is so low, and the hours are so long. But the Chinese had no choice and no jobs in other places.”

Chen noted that the Chicago Cafe’s menus, which have changed little throughout its history, never served traditional Chinese dishes. Few restaurants in China serve Chicago Cafe staples like chop suey and egg foo young, let alone its broad selection of American classics like steak and eggs and hamburger with fries. The culinary choices cater to Americans’ perception and preference of Chinese food, Chen said, which isn’t atypical of popular 20th century Chinese diners whose “main purpose is economic”.

“If they can make a living serving Chinese food, they’ll do it,” he said. “If they can make a living serving french fries, they’ll do it.”

Hints of discrimination were evident in the records unearthed at Chicago Cafe. Harley Spiller, a museum educator and collector from New York City who flew into Woodland the night before, noticed that some Chicago Cafe menus advertised “American food and chop suey” but omitted mentions of “Chinese food”. Other iterations divided American and Chinese dishes into separate columns, Spiller said, which some scholars have attributed to racism. “You wouldn’t mix and match,” he said.

Elizabeth Chin, an anthropologist and the sister of Jack Chin, said the typeface and phone numbers printed on said menus also offer valuable clues to the restaurant’s past. A three-digit number appeared on a few different Chicago Cafe menu sets, and a four-digit number appeared on a stack of order sheets. These types of phone numbers first appeared in the city directory at the turn of the 20th century. Chin, also an ethnographer, said that the Art Nouveau style heading of these menu sets suggested a possible origin date in the 1910s, when the arched, calligraphic fonts became popularized.

Ben Ruilin Fong, a comparative literature PhD candidate at UC Davis who is of no relation to the restaurant owners, said the Fongs seemed to be constantly negotiating with their identity as natives of Taishan, a city in China’s Guangdong province known as the “first home of overseas Chinese”. Like many others from the region, the Fongs fled to British-ruled Hong Kong, then the US, in search of new opportunities. “It’s interesting how they kept emphasizing they’re from Hong Kong rather than Guangzhou or Taishan,” Ben Ruilin Fong said, scanning a 1975 feature in a local paper. Taishanese immigrants, he said, often leverage their connection to Hong Kong, a city of higher status and class, to feel a sense of pride and heritage.

Paul and Nancy have two adult children: Amy, who became a physical therapist, and Andy, a software engineer. Neither will be taking over the reins, but Fong, 75, said he’s not concerned that the business his grandfather built more than 120 years ago might end with him. “I want to retire and spend more time with my grandchildren,” he said.

Amy Fong described the recent media buzz, which drew hordes of new diners to the establishment, as a “blessing and a curse”. Lunch rush is busier than it’s been in decades, with retirees filling every booth and bar seat. The restaurant’s lone waitress, Dianna Olstad, rushed to deliver orders of chop suey, pork chow mein and ginger beef to the kitchen.

Like many Chinese restaurant workers, the Fongs worked punishing hours. Many decades ago, when Amy’s grandfather, John, was in charge, the Chicago Cafe operated from 5.30 am, to serve breakfast to farmers, until 3am, to serve patrons of nearby bars. For most of their adult lives, her parents never took a vacation, Amy Fong said. As they age, she’s increasingly worried about their health – her grandmother died of a heart attack in the kitchen when she was 63.

“They’re very stoic people,” Fong said. “They don’t talk much about their personal desires, hopes and dreams.”

For some regulars who have been frequenting the Chicago Cafe for generations, the restaurant’s historic value is incalculable. Cindy Bueno, 74, started coming to the Chicago Cafe in the late 1950s, when their mother began working there as a waitress. For nearly the entirety of their adolescence, Bueno and her six sisters spent their afternoons at the restaurant, finishing homework or helping their mother wash dishes, chop onions and other simple chores. In 1968, Bueno held her wedding reception there, and everybody ate chicken fried steak. Years later, her children attended high school with Amy and Andy Fong. “Everyone who comes here has a history of Chicago Cafe,” Bueno said. “This place is unforgettable.”

Despite his team’s laborious research efforts, Chin said, it may ultimately be impossible to definitively verify that Chicago Cafe is the oldest in the nation. Official documentation simply doesn’t exist: Woodland city directories excluded Asian residents and businesses until 1939, which Chin said is likely an indication that officials didn’t consider Chinese people important enough to document.

The strongest piece of evidence supporting a 1903 origin date, he said, is a 1940 report from the Woodland Daily Democrat: “For over 37 years, the Chicago Restaurant has served Woodland well with the finest of foods at extremely low prices.” (No living Fong knows the story behind the restaurant’s name, though Jack Chin said that “Chicago” was a common name for Chinese restaurants because the city had a reputation for serving superb Chinese cuisine.)

The date “1904” appeared twice in the trove of artifacts Chin’s team uncovered at the restaurant, on a business card and in a cryptic handwritten letter, but neither amounts to actual proof. But even without documentary evidence, Chin said he’s fairly certain that a 1903 origin date is accurate. Still, he isn’t giving up on his search. “We’re going to explore more long shot research directions,” he said.

Paul Fong, though, had surprisingly little to say about Chin’s quest to solidify his family’s legacy. His mind was more occupied by matters of culinary interest. As the lunch crowd thinned, he began clearing tables and chatting with regulars. When two women praised his chop suey, he gave them a brief overview of how the dish has evolved in the US. The traditional Cantonese version that his family has served for more than a century, he told them, incorporates bean sprouts. But most restaurants today, he said with a shake of the head, make the “New Hong Kong” variety that tastes like spaghetti. “Everyone from Sacramento, Dixon – they all come for our old Cantonese style chop suey,” he said.

Oil and gas equipment intended to cut methane emissions is preventing scientists from accurately detecting greenhouse gases and pollutants, a satellite image investigation has revealed.

Energy companies operating in countries such as the US, UK, Germany and Norway appear to have installed technology that could stop researchers from identifying methane, carbon dioxide emissions and pollutants at industrial facilities involved in the disposal of unprofitable natural gas, known in the industry as flaring.

Flares are used by fossil fuel companies when capturing the natural gas would cost more than they can make by selling it. They release carbon dioxide and toxic pollutants when they burn as well as cancer-causing chemicals.

Despite the health risks, regulators sometimes prefer flaring to releasing natural gas – which is 90% methane – directly into the atmosphere, known as “venting”.

The World Bank, alongside the EU and other regulators, have been using satellites for years to find and document gas flares, asking energy companies to find ways of capturing the gas instead of burning or venting it.

The bank set up the Zero Routine Flaring 2030 initiative at the Paris climate conference to eradicate unnecessary flaring, and its latest report stated that flaring decreased by 3% globally from 2021 to 2022.

But since the initiative, “enclosed combustors” have begun appearing in the same countries that promised to end flaring. Experts say enclosed combustors are functionally the same as flares, except the flame is hidden.

Tim Doty, a former regulator at the Texas Commission on Environmental Quality, said: “Enclosed combustors are basically a flare with an internal flare tip that you don’t see. Enclosed flaring is still flaring. It’s just different infrastructure that they’re allowing.

“Enclosed flaring is, in truth, probably less efficient than a typical flare. It’s better than venting, but going from a flare to an enclosed flare or a vapour combustor is not an improvement in reducing emissions.”

The only method of detecting flaring globally is by using satellite-mounted tools called Visible Infrared Imaging Radiometer Suite of detectors (VIIRS), which find flares by comparing heat signatures with bright spots of light visible from space.

But when researchers tried to replicate the database, they saw that the satellites were not picking up the enclosed flares.

Eric Kort, an associate professor at the University of Michigan, said: “The VIIRS satellite database is still the standard product that scientists use globally. It’s the best, most consistent product we currently have.

“If you enclose the flare, people don’t see it, so they don’t complain about it. But it also means it’s not visible from space by most of the methods used to track flare volumes.”

Without the satellite data, countries were forced to rely mostly on self-disclosed reporting from oil and gas companies, researchers said. Environmentalists fear the research community’s ability to understand pollution and greenhouse gas emissions from the energy sector could be jeopardised.

Colorado became the first and only US state to ban routine flaring in 2021. But Maxar satellite imagery shows enclosed flares replacing open-lit flares in the run-up to the Colorado ban on flaring, which provided a carve-out clause for enclosed flaring devices.

Google Earth historical images of one site in Jackson County, Colorado, show a lit flame disappearing and being replaced with an enclosed flaring device. Because the flaring within the site is not detectable, it is difficult for researchers to determine when it is burning and for what purpose.

The NGO Earthworks, with an optical gas-imaging camera usually used by industry specialists looking for emissions leaks, recorded footage showing invisible pollutants coming from the device. However, the site’s owner, Fulcrum Energy Capital Funds, told the Guardian it had eliminated flaring from its facilities.

Methane and carbon dioxide plumes were seen coming from enclosed flaring devices in the Four Corners region of New Mexico, according to satellite data from CarbonMapper, which provides publicly accessible data on greenhouse gases.

In November 2023, the EU announced a plan to phase out routine flaring as part of legislation designed to tackle methane emissions. But enclosed flares have started to appear in the EU, with information from oil and gas equipment supplier websites suggesting the devices are being sold in multiple member states.

Satellite images show enclosed flares at Ineos facilities in Grangemouth, Scotland, and the Ineos Rafnes refinery in Norway. In Germany, enclosed flares can be seen at facilities owned by the steel manufacturer ArcelorMittal.

An Ineos spokesperson said the enclosed flare “leads to significantly less noise being emitted and much lower luminosity”, adding that these things were important for communities living and working close to its sites.

An ArcelorMittal spokesperson said: “We installed an enclosed flaring device as a precautionary measure, so that the flare is not visible from a distance if gas had to be flared at night.” The device had a 100% combustion rate andno measurable emissions, the company added.

Zubin Bamji, the programme manager of the World Bank’s Global Flaring and Methane Reduction Partnership, said volumes from enclosed flares were “very small and are unlikely to have a significant impact on flare volume estimates at a regional, country or global level”, but confirmed that VIIRS did not classify enclosed flaring devices as flares.

A source with knowledge of upcoming EU methane legislation said it “covers all flares, not just those detectable by satellite”, and added that flaring in emergency situations would still be allowed.

It was not immediately clear how the EU would determine whether flaring inside enclosed flares was routine or for emergency situations.

• This article was funded by Journalismfund Europe, the Fund for Investigative Journalism, and supported by the Arena Climate Network.

There was something wrong with the chimpanzees. For weeks, a community of 205 animals in Uganda’s Kibale national park had been coughing, sneezing and looking generally miserable. But no one could say for sure what ailed them, even as the animals began to die.

Necropsies can help to identify a cause of death, but normally, the bodies of chimps are found long after decomposition has set in, if at all. So when Tony Goldberg, a US wildlife epidemiologist visiting Kibale, got word that an adult female named Stella had been found freshly dead, he knew this was a rare opportunity to look for an answer.

Goldberg and two Ugandan veterinary colleagues drove for two hours to a remote part of the park, then lugged their gear for another hour through the forested terrain to where Stella’s body lay. They lifted the 45kg animal on to a tarpaulin, and got to work. Crouching over the chimp – sweating beneath their full-body protective suits, their goggles fogging in the humid air – they meticulously worked through Stella’s organ systems, collecting samples. Not knowing what had killed her was “unnerving”, Goldberg recalls. “It could have been Ebola.”

As the necropsy progressed, however, Goldberg began to see telltale signs of a familiar disease: fluid buildup in Stella’s chest cavity and around her heart; lung tissue that was dark red, consolidated and marked with lesions. It looked like the chimp had died of severe pneumonia.

Months later, molecular testing revealed the culprit: human metapneumovirus (HMPV), one of a collection of viruses that presents in people as a common cold but is “a well-known killer” in our closest primate relatives, says Goldberg, a researcher at the University of Wisconsin-Madison. More than 12% of the community that Stella belonged to died in the outbreak. Others were lost as a result of being orphaned. “Stella had a baby that was clinging to her body for a while after she died,” Goldberg says. “The baby subsequently died.”

This phenomenon of animals catching diseases from humans, called reverse zoonoses, affects species around the world – from mussels contaminated with hepatitis A virus to tuberculosis transmitted to Asian elephants. But because of their evolutionary closeness to humans, great apes tend to be most vulnerable.

For some great ape populations that live in protected areas, reverse zoonoses are an even bigger threat than habitat loss or poaching. In a group at Kibale, for example, respiratory pathogens such as human rhinovirus C and HMPV have been the leading chimp killers for more than 35 years, accounting for almost 59% of deaths from a known cause.

For conservationists, the phenomenon presents a thorny problem. In many places in Africa, people live in close proximity to great apes. Great ape tourism has also become a central pillar of these endangered species’ conservation: ensuring habitats are preserved and local people are incentivised to support wildlife. But the same industry that funds protection of many apes could also be helping to drive them towards extinction, as close proximity to humans can expose the animals to deadly pathogens.

Tourism is necessary for conservation, says Gladys Kalema-Zikusoka, a wildlife veterinarian and founder of Conservation Through Public Health, a nonprofit group in Entebbe, Uganda. “But it needs to be done carefully, otherwise we won’t have these animals around.”

Some of the first records of reverse zoonoses in great apes were made by British primatologist Jane Goodall. In 1986, Goodall wrote that chimps “quite often” had colds and coughs, and “can contract the same contagious diseases as humans”. But conclusive evidence that chimps were being infected by people didn’t arrive until 2008, when Fabian Leendertz, the director of the Helmholtz Institute for One Health in Greifswald, Germany and his colleagues used molecular tools to show that human viruses were to blame for a decade’s worth of major respiratory disease outbreaks in chimps in Taï national park, Côte d’Ivoire.

Since the paper came out, habitat destruction, human encroachment, the climate crisis and globalisation have only accelerated, and all of Africa’s great ape species are now decreasing. Eastern and western gorillas are both critically endangered, while chimpanzees and bonobos are endangered. The fact that human diseases can take out significant proportions of great ape communities makes the pathogens a dire threat to all four species. “Great ape populations can’t afford these sorts of losses,” Goldberg says. “Their populations are already so small, fragmented and declining that they just don’t have the ability to rebound or adapt.”

Many of the pathogens cause infections that, in a person, would result in an annoying but mild cold. In great apes, however, these diseases can be deadly, because the animals have no immunity or evolved genetic resistance. Once a chimpanzee or gorilla becomes unwell, there is usually little that can be done to help. There are also no vaccines for most common cold viruses.

What could work, Goldberg realised, was a public-health approach: finding the source of pathogens and preventing them from getting into the populations in the first place.

In 2015, the International Union for Conservation of Nature (IUCN) released guidelines for great ape tourism, recommending that people stay at least 7 metres away from animals, tour groups limit their size, all visitors wear face masks and people who feel unwell be excluded.

But there are obvious reasons why that doesn’t always happen. For one, it relies on honesty from international visitors. “Imagine you’re an American tourist, you’ve gone all the way to Africa, and this is your bucket-list trip,” Goldberg says. “Now you’ve got a stomach ache – and you’re not going to go see the gorillas? Of course you are.”

Tourists often break rules while out in the field, either because of excitement in the moment or wilful disregard. “Some tourists just don’t listen,” says Kalema-Zikusoka. And local guides might or might not correct them. “They don’t want to be rude, and they find it hard to manage tourists.”

Guides may also refrain from reproaching visitors for fear of losing a potential tip. Some guides “get tips that are twice the monthly salary of typical villagers in the area”, Goldberg says. “There are all these perverse incentives.”

One 2020 study that analysed 282 YouTube videos of mountain gorilla tourism found that 40% depicted humans within arm’s reach of gorillas or engaging in physical contact with the animals.

In another 2020 study, Darcey Glasser, then a graduate student at Hunter College of the City University of New York, joined 101 chimp treks at Kibale. Glasser observed tourists coughing during 88% of excursions; sneezing in 65%; and urinating in 37%. “Everyone’s touching everything,” she says.

Glasser presented her findings to wildlife officials in Uganda, who responded encouragingly, she says, adding hand-sanitising stations at the start of trails. In general, however, officials tend to avoid imposing strict rules that they think may impact visitors’ experiences.

Great ape tourism is a key source of revenue for the 13 African countries where it occurs, Leendertz says, so reverse zoonosis is “not always an easy topic”. Officials at the Uganda Wildlife Authority, which oversees the country’s national parks and all tourism activity in them, did not respond to multiple interview requests.

Ecotourism represents one serious disease risk for great apes, but it cannot account for all cases of reverse zoonoses. Some great ape populations never see a tour group – Stella’s community among them – yet still experience deadly outbreaks of human pathogens.

As Goldberg thought about how to tackle this problem, he noticed a perplexing pattern in the list of human pathogens that typically afflict great apes: they’re the infections that, like clockwork, young children catch when they go back to school, and then bring home.

Great apes, it occurred to him, could be catching diseases from adults who go into the forest after catching pathogens from their children. The idea seemed even more plausible when Goldberg realised that adults infected with these “sniffle germs” often show no symptoms, even as they shed copious viral particles.

Goldberg secured a grant for new research, led by Taylor Weary, an epidemiologist who recently graduated from Goldberg’s lab, alongside Patrick Tusiime, health coordinator for the Kasiisi Project, a nonprofit group that supports primary schools around Kibale. They compared monthly nasal swabs from local schoolchildren, parents who worked in the forest, and faecal samples from the chimps.

The findings, which are now in review for publication, confirmed Goldberg’s original hypothesis. Every respiratory pathogen that has caused a chimp outbreak in Kibale was present in children living nearby. Then, during Uganda’s most stringent Covid-19 lockdown between March and September 2020, the researchers observed an “extraordinarily clear” drop in infections across the board, Goldberg says, suggesting that schools are indeed a major source of transmission.

The message, Goldberg says, was clear: “To save the chimps, we have to make kids healthier.”

One big takeaway from the findings was that the current model is inadequate to reduce the risk of reverse zoonoses in Kibale’s chimpanzees, and probably in great apes in Africa as a whole. It hinges on stopping symptomatic people from going into the forest, but infected adults are usually asymptomatic. Forbidding guides and trackers from working whenever their children are ill isn’t a solution, Goldberg says: kids “are sick all the time”.

Banning tourism also wouldn’t work. Parks depend on visitor fees to pay salaries, maintain local support for conservation and justify the cost of setting land aside for wildlife. “When I was growing up, the perception was that chimps are bad,” says Tusiime, who was born in a rural village near Kibale. “Now there’s a shift to a positive attitude towards chimpanzees because they bring in tourists, they bring in revenue.”

Focusing on making children living near great apes healthier, then, could be the best bet for keeping human diseases out of great ape populations. Programmes have already been launched to reduce transmission among local children, teaching handwashing and other hygiene measures.

Scientists also believe that enforcement of existing biosecurity rules could go a long way toward reducing transmission – but that will require focused commitment from African governments and tourism providers, says Cristina Gomes, a wildlife conservationist at Florida International University in Miami who helped launch a working group to identify new strategies. One idea is to entitle guides working with chimps to paid sick days – a luxury most do not have. Another suggestion is to certify companies that follow best practices, justifying a slightly higher fee for their services.

Common cold viruses cannot be eradicated, and people and great apes won’t be staying apart anytime soon. Goldberg says outbreaks of respiratory disease were documented in chimps in at least five locations throughout sub-Saharan Africa in 2023 alone.

The hope, however, is that these will become rarer as scientists, officials, rural residents and tourists gain a deeper understanding of the problem. “Behavioural change takes time, but if you’re committed, it eventually happens,” Tusiime says. “So we need to start now.”

A version of this report was previously published in Nature

You might visit Amsterdam for its canals, and who could blame you, really. But the truly interesting waterways aren’t under your feet – they’re above your head.

Beautiful green roofs have popped up all over the world: specially selected plants growing on structures designed to manage the extra weight of biomass. Amsterdam has taken that one step further with blue-green roofs, specially designed to capture rainwater. One project, the resilience network of smart, innovative, climate-adaptive rooftops (Resilio), has covered more than 9,000 sq metres (100,000 sq ft) of Amsterdam’s roofs, including 8,000 sq metres on social housing complexes. Citywide, the blue-green roof coverage is even bigger, estimated at more than 45,000 sq metres.

The “sponge city” concept is becoming increasingly popular. Planners deploy more green spaces that soak up downpours that are getting heavier as the world warms. That simultaneously reduces flooding and recharges the underlying layer of absorbent rock, which can then be tapped into in times of need. Whereas cities used to be designed to divert rainwater away as quickly as possible, increasingly, they are exploiting that resource.

A big challenge with sponge cities is that so much of an urban area is rooftops. Green roofs will soak up some rainwater to hydrate the plants there, but blue-green roofs go a step further, with infrastructure that gathers the liquid, stores it and dispenses it to the building’s residents for watering plants and flushing toilets.

The system works in layers. At the surface, you have plants: some combination of mosses, shrubs, grasses, ferns, herbs and sedum, a hardy genus that’s a staple of green roofs. (While plants need sunlight to survive, on a roof, they can be bombarded with too much light. It can also get hot and windy up there.) The plants are rooted in soil, providing nutrients and support.

Below that is a filter layer, which keeps the soil from getting into the next layer: a lightweight crate system that stores the water. Finally, below that are additional layers to keep water and plant roots from infiltrating the actual roof. “You have, in fact, a flat rain barrel on top of your roof,” says Kasper Spaan, policy developer for climate adaptation at Waternet, Amsterdam’s public water management organisation, which is participating in Resilio.

The water levels in the blue-green roof are managed by a smart valve. If the forecast says a storm is coming, the system will release stored water from the roof ahead of time. That way, when a downpour comes, the roof refills, meaning less rainwater enters the gutters and sewers in the surrounding area. In other words, the roof becomes a sponge that can be wrung out as needed. “In the ‘squeezable’ sponge city, you make the whole city malleable,” says Spaan.

This makes the traditional system of stormwater management more flexible, but also more complicated. So the Resilio project used software from Autodesk to model the impact of blue-green roofs and the risk of flooding in Amsterdam, also adjusting for climate breakdown.

“You can take a look at historical flood patterns and then you can do simulations that will help you understand. If I could take this much capacity out of the drainage network, when the storm comes, I’m going reduce flooding by 10, 15, 20%,” says Amy Bunszel, Autodesk’s executive vice-president of architecture, engineering and construction design solutions. “So our software allows them to do simulations and play with different trade-offs.”

Beyond the sponge-city benefits, blue-green roofs can cool the top floor of a building, essentially “sweating” off the stored water. With the right kinds of indigenous plant, they can help wildlife by catering to native pollinating insects. Going a step further, scientists are experimenting with growing crops on rooftops under solar panels, known as rooftop agrivoltaics. Theoretically, pairing that with blue-green systems could improve the efficiency of the solar panels by cooling them with the evaporating water.

Not every building can go blue-green. The additional infrastructure is not very heavy, but the water it holds is. So while it is relatively cheap and easy to build the system into new construction, accounting for the extra weight, older buildings may need retrofits to accommodate it. In the long term, it can save a building money by reducing the volume of water bought from a municipal system. Like any technology, its cost will fall as it is more widely deployed.

The idea is for places experiencing worsening droughts and flooding to deploy not only sponge city concepts on the ground – like patches of dirt with drought-tolerant plants to absorb stormwater into aquifers – but on top of their buildings as well. “We think the concept is applicable to many urban areas around the world,” says Spaan. “In the south of Europe – Italy and Spain – where there are really drought-stressed areas, there’s new attention for rainwater catchment.”

Cities could even incentivise blue-green roofs by providing tax breaks, rewarding building owners for reducing their contribution of stormwater to overburdened sewer and water systems. US cities such as Los Angeles and Pittsburgh have been rolling out something similar: taxes on the amount of impermeable area on a property, encouraging landowners to develop gardens and other green spaces.

The city of tomorrow, then, isn’t the concrete-smothered metropolis of science fiction, but an increasingly green and spongey landscape that can be squeezed in times of need. “Our philosophy in the end is not that on every roof, everything is possible,” says Spaan, “but that on every roof, something is possible.”

Rapidly rising levels of TFA, a class of “forever chemical” thought to damage fertility and child development, are being found in drinking water, blood and rain, causing alarm among experts.

TFA, or trifluoroacetic acid, is a type of per- and polyfluoroalkyl substance (PFAS), a group of human-made chemicals used widely in consumer products that do not break down for thousands of years. Many of the substances have been linked to negative effects on human health.

Studies from across the world are reporting sharp rises in TFA. A major source is F-gases, which were brought in to replace ozone-depleting CFCs in refrigeration, air conditioning, aerosol sprays and heat pumps. Pesticides, dyes and pharmaceuticals can also be sources.

“Everywhere you look it’s increasing. There’s no study where the concentration of TFA hasn’t increased,” said David Behringer, an environmental consultant who has studied TFA in rain for the German government.

“If you’re drinking water, you’re drinking a lot of TFA, wherever you are in the world … China had a 17-fold increase of TFA in surface waters in a decade, the US had a sixfold increase in 23 years.” TFA in rainwater in Germany has been found to have increased fivefold in two decades.

“I’m worried about this because we’ve never seen in recent history a chemical that’s accumulating in so many media at such a high rate,” said Hans Peter Arp from the Norwegian Geotechnical Institute and the Norwegian University of Science and Technology. “It’s accumulating in our tap water, the food we’re eating, plants, trees, the sea, and all in the past few decades.”

He added: “We all have been experiencing rising TFA concentrations in our blood since the Montreal protocol [banned CFCs]. Future generations will have increasing concentrations in their blood until some kind of global action is taken. Accumulation [in the environment] is essentially irreversible and I’m afraid the impact on humans and the environment won’t be recognised by scientists until it is too late.”

Last month, the German chemical regulator informed the European Chemicals Agency that it wanted TFA classified as reprotoxic, meaning it can harm human reproductive function, fertility and foetal development.

Denmark and Germany have set limits for TFA in drinking water but the UK has not. England’s water companies have been asked to assess their drinking water sources for 47 types of PFAS but TFA is not on the list.

Britain’s Health and Safety Executive has identified TFA as “a substance of concern, since there are indications that it might cause developmental toxicity” and the Environment Agency says it is planning a targeted programme to test for TFA in surface and groundwater.

A Department for Environment, Food and Rural Affairs spokesperson said it would continue to “assess levels of PFAS occurring in the environment, their sources, potential risks and to inform policy and regulatory approaches.

“Regulations require that drinking water must not contain any substance at a level which would constitute a potential danger to human health. Should TFA be detected in drinking water we would expect companies to react in the same way as for other PFAS compounds.”

But TFA is incredibly difficult to remove from water. “There’s no way to get TFA out,” said Behringer. “Reverse osmosis is massively expensive and not scalable, so the logical course is to stop the input.”

The European Fluorocarbons Technical Committee, representing the F-gas and chemicals industry, says TFA occurs naturally in large quantities in the environment. It says industrial use of TFA is limited and environmental releases are very low. It did not respond to a Guardian request for comment.

But these assertions have been disputed. The US Environmental Protection Agency says TFAs are a breakdown product of F-gases. Moreover, studies of Arctic ice cores show TFA levels have been rising sharply since F-gases replaced CFCs in the 1990s.

“Every time the industry says it’s natural, they quote certain scientific papers,” says Prof Shira Jourdan, an environmental analytical chemist at the University of Alberta. She said she had studied these decades-old papers and found they only suggested it was possible that TFA was naturally occurring because of a lack of knowledge of its origins at the time of the studies.

“None of the evidence says it’s natural,” said Jourdan. “When industry says it’s natural it’s a danger, because then no one takes accountability for the pollution.”

Ariana Spentzos, of the NGO Green Science Policy, said: “We’re following the familiar PFAS playbook by allowing reckless environmental contamination and only figuring out after the fact the trail of harm left behind. We are just beginning to understand the health hazards associated with TFA.”

Environmental groups are calling on the UK government to take more action to tackle PFAS substances. “PFAS presents a global chemical pollution crisis which requires urgent action,” said Hannah Evans, from the campaign group Fidra. “We’re calling on the UK government to prevent PFAS emissions at source, which includes revising both F-gas and pesticide regulations to phase out PFAS.”

The German Environment Agency recommends using natural refrigerants instead. Its president, Dirk Messner, said: “TFA is found everywhere – in water, soil, food and the human body. It does not break down and can hardly be removed from drinking water. However, TFA-forming chemicals are numerous and on the rise. Persistent substances from multiple sources like TFA fall through the regulatory cracks. To reduce the release of TFA into the environment, we need consistent, precautionary regulation, cross-sectoral minimisation and a substitution with TFA-free alternatives wherever possible.“

Blue-green algae, or cyanobacteria, come in many forms and have generally got a bad press, mainly because five of the 2,000 identified species can produce some of the deadliest toxins known to science.

At the same time, they are among the oldest organisms in the world, dating back 2.1bn years, and we owe them a debt of gratitude.

Cyanobacteria were the first organisms to use photosynthesis, turning carbon dioxide into oxygen. They are responsible for creating the oxygen-rich atmosphere that enabled life on Earth to flourish and humans to evolve.

In their untold trillions, in almost every environment where there is water, even on damp rocks in deserts, they continue this valuable service, keeping the atmosphere safe for mammals to breathe.

But in nutrient-rich water, created by farm waste or sewage released into rivers and lakes, blue-green algae multiply fast, especially in warm sunshine. This is dangerous in still waters where they form dense rafts of scum that deprive the waters below of oxygen, killing fish.

In some circumstances they also create toxins that can poison animals and humans that drink it. Only laboratory tests can establish whether such algae blooms are toxic but anyone seeing one is advised to avoid it and report its presence.

Campaigners are blaming developed countries for capitulating at the last minute to pressure from fossil fuel and industry lobbyists, and slowing progress towards the first global treaty to cut plastic waste.

Delegates concluded talks in Ottawa, Canada, late on Monday, with no agreement on a proposal for global reductions in the $712bn (£610bn) plastic production industry by 2040 to address twin issues of plastic waste and huge carbon emissions.

They agreed to hold more discussions before the last summit on the treaty in Busan, South Korea, in November.

But two years on from a historic agreement in Nairobi to forge a global treaty to cut plastic waste, delegates said countries were just wasting time. A proposal from Peru and Rwanda to address for the first time the scale of plastic production in order cut waste was supported by 29 countries including Australia, Denmark, Nigeria, Portugal, the Netherlands and Nigeria, who signed a declaration, “the Bridge to Busan”, calling on all delegates to ensure plastic production was addressed.

The UK and US did not support the proposal to cut plastic production.

Juliet Kabera, the director general of the Rwanda environment management authority, said: “Rwanda’s vision for the treaty is to achieve sustainable production of plastics. We need a global target based on science to measure our collective actions.”

But as talks headed into the night on Monday, there was no agreement on putting plastic production at the centre of the treaty.

David Azoulay, the director of environmental health at the Center for International Environmental Law (CIEL), said while a handful of countries had taken a stand to keep ambitious proposals alive, most countries accepted a compromise at the last minute that played into the hands of petrostates and industry influences.

“From the beginning of negotiations, we have known that we need to cut plastic production to adopt a treaty that lives up to the promise envisioned … two years ago,” he said. “In Ottawa, we saw many countries rightly assert that it is important for the treaty to address production of primary plastic polymers.

“But when the time came to go beyond issuing empty declarations and fight for work to support the development of an effective intersessional programme, we saw the same developed member states who claim to be leading the world towards a world free from plastic pollution, abandon all pretence as soon as the biggest polluters look sideways at them.”

The US was singled out for criticism for blocking talks on cutting plastic production.

“The United States needs to stop pretending to be a leader and own the failure it has created here,” said Carroll Muffett, the president of CIEL. “When the world’s biggest exporter of oil and gas, and one of the biggest architects of the plastic expansion, says that it will ignore plastic production at the expense of the health, rights and lives of its own people, the world listens.”

He said that despite signalling at the G7 summit this month that it would commit to reduce plastic production, in Ottawa the US failed to follow through on its promises.

The failure to pursue ambitious cuts to plastic production came after a record number of fossil fuel and petrochemical lobbyists attended the summit in Canada.

Graham Forbes, Greenpeace’s head of delegation to the global plastics treaty negotiations, said: “The world is burning and member states are wasting time and opportunity. We saw some progress, aided by the continued efforts of states such as Rwanda, Peru, and the signatories of the Bridge to Busan declaration in pushing to reduce plastic production.

“However, compromises were made on the outcome which disregarded plastic production cuts, further distancing us from reaching a treaty that science requires and justice demands.”

Rich Gower, a senior economist at the NGO Tearfund, said: “An ambitious and effective treaty is still possible, but negotiations are on a knife-edge: time is short and strong opposition remains from the petrochemicals industry and states connected with it, even as their products pile up on street corners and in watercourses around the world.”

Representatives of the petrochemical industry said they were committed to a global treaty to cut plastic waste. But they pushed back on reductions in plastic production, an industry worth $712bn in 2023.

Chris Jahn, the council secretary of the International Council of Chemical Associations (ICCA), speaking on behalf of the industry group Global Partners for Plastics Circularity, said: “Our industry is fully committed to a legally binding agreement all countries can join that ends plastic pollution without eliminating the massive societal benefits plastics provide for a healthier and more sustainable world. We will continue to support governments’ efforts by bringing forth science-based and constructive solutions that leverage the innovations and technical expertise of our industry.”