Donald Trump escalated his personal insults against Kamala Harris at a Wednesday evening rally in Georgia as he faces growing scrutiny over reports of his praise of Hitler and alleged sexual misconduct.

“This woman is crazy,” the former president said at an event in the Atlanta suburb of Duluth, hosted by Turning Point USA, a far-right youth group. He said voters should stand up to the vice-president and tell her: “You’re the worst ever. There’s never been anybody like you. You can’t put two sentences together. The world is laughing at us because of you.” He also said that in her recent interview with CBS, she “gave an answer that was from a loony bin”, later adding: “She’s not a smart person. She’s a low IQ individual.”

The rally, less than two weeks before election day, came after the Guardian published an interview with a former model who accused Trump of groping her at Trump Tower in 1993 after notorious sexual abuser Jeffrey Epstein introduced them, an allegation the Trump campaign denied. Stacey Williams said it felt as if the unwanted touching was part of a “twisted game” between the two men and that it appeared Epstein and Trump were “really, really good friends and spent a lot of time together”.

Williams’s account put the spotlight back on the roughly two dozen women who have accused Trump of sexual misconduct throughout his career. Harris, campaigning with Republican former congresswoman Liz Cheney, who has sought to encourage Republican women to support the Democrat.

The Georgia rally also came after Harris’s surprise speech in Washington DC on Wednesday, when she denounced the former president as a “fascist” who wants “unchecked power”. John Kelly, Trump’s former chief of staff and a retired Marine general, told the New York Times this week that he believed Trump met the definition of “fascist” and was “certainly an authoritarian”. He also said Trump repeatedly commented: “Hitler did some good things, too.”

In a characteristically rambling speech, Trump went on meandering tangents about Google (“Google is treating us much better. Do you notice that? What happened to Google?”); McDonald’s (“McDonald’s was one of the most viewed things that [Google] ever had”); Emmanuel Macron (“I stopped wars with France”); Richard Nixon (“That was not good when they found out he taped every single conversation”); and the vice-president’s name (“You can’t call her ‘Harris’ because nobody knows who the hell you’re talking about”).

He threatened to sue CBS’s 60 Minutes, repeating false claims that the station manipulated Harris’s interview after Trump backed out of his planned interview with the program. He reiterated the threat a second time about an hour later in his speech.

Robert F Kennedy Jr, former independent presidential candidate, also rallied for Trump in Georgia, calling Kelly a “known liar”. Trump did not address Kelly at the rally, but on Truth Social called his former chief of staff a “LOWLIFE” and “total degenerate”.

In a “faith-focused” town hall in Zebulon, Georgia earlier on Wednesday, Trump praised Viktor Orbán, Hungary’s nationalist prime minister who has been condemned for undermining democratic institutions and aligning with Moscow and Beijing.

Asked about his faith, Trump responded: “When you believe in God, it’s a big advantage over people that don’t have that.” He went on to falsely suggest he has endured more investigations than notorious gangster Al Capone.

A former model who says she met Donald Trump through the late sexual abuser Jeffrey Epstein has accused the former president of groping and sexually touching her in an incident in Trump Tower in 1993, in what she believed was a “twisted game” between the two men.

Stacey Williams, who worked as a professional model in the 1990s, said she first met Trump in 1992 at a Christmas party after being introduced to him by Epstein, who she believed was a good friend of the then New York real estate developer. Williams said Epstein was interested in her and the two casually dated for a period of a few months.

“It became very clear then that he and Donald were really, really good friends and spent a lot of time together,” Williams said.

The alleged groping occurred some months later, in the late winter or early spring of 1993, when Epstein suggested during a walk they were on that he and Williams stop by to visit Trump at Trump Tower. Epstein was later convicted on sex offenses and killed himself in prison in 2019.

Moments after they arrived, she alleges, Trump greeted Williams, pulled her toward him and started groping her. She said he put his hands “all over my breasts” as well as her waist and her buttocks. She said she froze because she was “deeply confused” about what was happening. At the same time, she said she believed she saw the two men smiling at each other.

Karoline Leavitt, the press secretary for Donald Trump’s campaign, provided a statement denying the allegations, which said in part: “These accusations, made by a former activist for Barack Obama and announced on a Harris campaign call two weeks before the election, are unequivocally false. It’s obvious this fake story was contrived by the Harris campaign.”

Williams says that Trump sent her agent a postcard via courier later in 1993, an aerial view of Mar-a-Lago, his Palm Beach residence and resort. She shared it with the Guardian. In his handwriting – using what appears to be his usual black Sharpie – he wrote: “Stacey – Your home away from home. Love Donald”.

Williams, who is 56 and a native of Pennsylvania, has shared parts of her allegation on social media posts in the past, but revealed details about the alleged encounter on a call on Monday organized by a group called Survivors for Kamala, which supports Democratic presidential nominee Kamala Harris. The Zoom call featured actor Ashley Judd and law professor and academic Anita Hill, among others. Survivors for Kamala also took out an ad in the New York Times this week, signed by 200 survivors of sexual and gender violence, which was meant to serve as a reminder that Trump has been found liable for sexual abuse in a court.

After the alleged incident, Williams said that she and Epstein left Trump Tower, and that she began to feel Epstein growing angry at her.

“Jeffrey and I left and he didn’t look at me or speak to me and I felt this seething rage around me, and when we got down to the sidewalk, he looked at me and just berated me, and said: Why did you do that?” she said on the Zoom call.

“He made me feel so disgusting and I remember being so utterly confused,” she said.

She described how the alleged incident seemed to her to be part of a “twisted game”.

“I felt shame and disgust and as we went our separate ways, I felt this sensation of revisiting it, while the hands were all over me. And I had this horrible pit in my stomach that it was somehow orchestrated. I felt like a piece of meat,” she said in an interview with the Guardian.

She and Epstein parted ways soon after. Williams said she never had any knowledge of his pattern of sexual abuse, which would later become known. Epstein is now considered one of the worst and most prolific pedophiles in modern history.

The allegation of groping and unwanted sexual touching follows a well-documented pattern of behavior by Trump.

About two dozen women have accused the former president, who has been convicted of multiple felonies, of sexual misconduct dating back decades. The allegations have included claims of Trump kissing them without their consent, reaching under their skirts, and, in the case of some beauty pageant contestants, walking in on them in the changing room.

A former model named Amy Dorris shared allegations about Trump similar to what Williams described in an interview with the Guardian in 2020. Trump denied ever having harassed, abused or behaved improperly toward Dorris.

Last year, a jury found Trump liable for sexually abusing the columnist E Jean Carroll in 1996 and awarded her $5m in a judgment.

Williams’ allegations raise new questions about Trump’s relationship with Epstein.

No evidence has surfaced that Trump was aware of or involved in Epstein’s misconduct.

But Trump and Epstein knew each other for decades and were photographed at the same social events in the 1990s and early 2000s, years before Epstein pleaded guilty in Florida in 2008 to state charges of soliciting and procuring a minor for prostitution.

“I’ve known Jeff for 15 years. Terrific guy,” Trump told New York magazine in 2002. “He’s a lot of fun to be with. It is even said that he likes beautiful women as much as I do, and many of them are on the younger side.”

After Epstein was arrested on sex-trafficking charges in 2019, Trump told journalists in the Oval Office that he “knew him, like everybody in Palm Beach knew him” but that he had a “falling out” with Epstein in the early 2000s.

“I haven’t spoken to him in 15 years,” Trump said. “I was not a fan of his, that I can tell you.”

Asked whether she had considered coming forward in the past, as other women were making allegations against Trump, Williams said she was a person who wanted to avoid negative attention or risk the backlash many other survivors have faced.

“I left the business,” she said. “I disappeared on purpose because I love being anonymous and I love my life of being a private citizen. Then I watched what has happened to women who come out and it is so horrifying and abusive. The thought of doing that, especially as a mother with a child in my house, was just not possible,” she told the Guardian.

“I just chose in my own way – comments on social media to contradict people who said he didn’t do anything,” she said.

Like other survivors, she said, she has processed what happened to her and became more confident about facing an angry backlash, she said.

Williams spoke about the allegations to at least two friends who spoke to the Guardian. One friend, who asked not to be named, said Williams told her about the alleged incident in 2005 or 2006 during a conversation in which Williams mentioned knowing Epstein, and how he had introduced her to Trump. The friend specifically remembers Williams telling her that she had been groped by Trump. Epstein was not a household name at the time, but the friend would later recall the anecdote when the Epstein scandal erupted.

“What I recall is that it was groping … what we would call feeling someone up,” the friend said.

Ally Gutwillinger, another longtime friend, said Williams told her about the alleged incident in 2015. Gutwillinger remembers the timing because Trump had announced that he was running for president.

“I went to her house sometime in that week and I saw a postcard of Mar-a-Lago and I said: ‘What’s this?’ and she said ‘Turn it over,’” Gutwillinger said. “She said something like: ‘He’s vile, he groped me in Trump Tower.’”

Kamala Harris has denounced Donald Trump as a “fascist” who wants “unchecked power” and a military personally loyal to himself after allegations emerged about the former president’s repeatedly-voiced admiration for Hitler.

On Wednesday, the vice-president gave a surprise speech from her Washington DC residence, doing so in the aftermath of reports that John Kelly, Trump’s former chief of staff, recalled how Trump lamented not having generals who swore loyalty to him in the same manner as military commanders served Hitler in Nazi Germany.

“Donald Trump is increasingly unhinged and unstable, and in a second term, people like John Kelly would not be there to be the guardrails against his propensities and his actions. Those who once tried to stop him from pursuing his worst impulses would no longer be there and no longer be there to rein him in,” Harris said.

Harris said that the remarks relayed by Kelly showed that Trump “does not want a military that is loyal to the United States constitution”.

“He wants a military who will be loyal to him, personally, one that will obey his orders, even when he tells them to break the law or abandon their oath to the constitution of the United States,” she said.

Posing the question as a stark choice for US voters going to the polls for the presidential election on 5 November, she added: “We know what Donald Trump wants. He wants unchecked power. The question in 13 days will be what do the American people want.”

Harris’s address came after she had spent more than a week highlighting Trump’s earlier branding of his political opponents as “the enemy within” and demands for the military to be deployed those who cause election “chaos”.

In on-the-record taped conversations with the New York Times, Kelly – who was White House chief of staff for 18 months during Trump’s presidency – said his former boss repeatedly praised Hitler, even when contradicted, and fitted the dictionary definition of a fascist.

“He commented more than once that: ‘You know, Hitler did some good things, too,’” said Kelly, who also said that Trump would rule as a dictator if elected again.

Kelly, a retired four-star Marine general, made similar remarks in an interview with the Atlantic.

Referencing the various reporting, Harris said: “It is deeply troubling and incredibly dangerous that Donald Trump would invoke Adolf Hitler, the man who is responsible for the deaths of 6 million Jews and hundreds of thousands of Americans. This is a window into who Donald Trump really is, from the people who know him best.”

She added: “It is clear from John Kelly’s words that Donald Trump is someone who, I quote, certainly falls into the general definition of fascists, who, in fact, vowed to be a dictator on day one and vowed to use the military as his personal militia to carry out his personal and political vendettas.”

It was the second time in a week that Harris had, in effect, labelled the Republican nominee a fascist. Last week, she answered affirmatively when a Detroit radio interviewer who asked if Trump’s vision amounted to fascism – although she did not utter the word directly.

Trump’s spokesperson has denied Kelly’s claims that Trump said this, calling it “absolutely false”.

Harris’s remarks on Wednesday were the clearest sign yet that she had changed tactics from a previous approach initially adopted after becoming her party’s nominee, when she and her surrogates attempted to play down and belittle Trump. In one example, by mocking his obsession with crowd sizes at his rallies.

Theories abound as to what Harris could do to turn voters away from Trump’s appeal, which has centered on vows to lower prices that rose during Joe Biden’s presidency and throw immigrants out of the country.

In an interview earlier today on CNN, the noted Republican pollster Frank Luntz said that the very sort of message Harris pushed this afternoon was not working.

“What’s interesting is that [when] Harris focused on why she should be elected president, that’s when the numbers grew,” Luntz said.

“And then the moment that she turned anti-Trump and focused onto him and said, don’t vote for me, vote against him, that’s when everything froze.”

Kelly’s characterisation of Trump as a fascist echoes that of Gen Mark Milley, the retired former chair of the armed services joint chiefs of staff. Milley, who Trump has said should be executed, is quoted by the journalist Bob Woodward in a recently published book as calling Trump “a total fascist” and “fascist to the core”.

Later on Wednesday, it was reported that Harris told NBC News that she was preparing for the possibility that Donald Trump will declare victory before the election is complete, saying: “We will deal with election night and the days after as they come, and we have the resources and the expertise and the focus on that.”

Also, at the White House daily media briefing, the press secretary. Karine Jean-Pierre, acknowledged that Biden agreed with those who say Trump is a fascist.

“I mean, yes,” Jean-Pierre replied, when a reporter put the question to her in the White House briefing room. She went on to argue that Trump himself has made no secret of how he would like to govern, saying: “The former president has said he is going to be a dictator on day one. We cannot ignore that … we cannot ignore or forget what happened on January 6 2021.”

Cecilia Nowell contributed reporting

The mother of a teenager who killed himself after becoming obsessed with an artificial intelligence-powered chatbot now accuses its maker of complicity in his death.

Megan Garcia filed a civil suit against Character.ai, which makes a customizable chatbot for role-playing, in Florida federal court on Wednesday, alleging negligence, wrongful death and deceptive trade practices. Her son Sewell Setzer III, 14, died in Orlando, Florida, in February. In the months leading up to his death, Setzer used the chatbot day and night, according to Garcia.

“A dangerous AI chatbot app marketed to children abused and preyed on my son, manipulating him into taking his own life,” Garcia said in a press release. “Our family has been devastated by this tragedy, but I’m speaking out to warn families of the dangers of deceptive, addictive AI technology and demand accountability from Character.AI, its founders, and Google.”

In a tweet, Character.ai responded: “We are heartbroken by the tragic loss of one of our users and want to express our deepest condolences to the family. As a company, we take the safety of our users very seriously.” It has denied the suit’s allegations.

Setzer had become enthralled with a chatbot built by Character.ai that he nicknamed Daenerys Targaryen, a character in Game of Thrones. He texted the bot dozens of times a day from his phone and spent hours alone in his room talking to it, according to Garcia’s complaint.

Garcia accuses Character.ai of creating a product that exacerbated her son’s depression, which she says was already the result of overuse of the startup’s product. “Daenerys” at one point asked Setzer if he had devised a plan for killing himself, according to the lawsuit. Setzer admitted that he had but that he did not know if it would succeed or cause him great pain, the complaint alleges. The chatbot allegedly told him: “That’s not a reason not to go through with it.”

Garcia attorneys wrote in a press release that Character.ai “knowingly designed, operated, and marketed a predatory AI chatbot to children, causing the death of a young person”. The suit also names Google as a defendant and as Character.ai’s parent company. The tech giant said in a statement that it had only made a licensing agreement with Character.ai and did not own the startup or maintain an ownership stake.

Tech companies developing AI chatbots can’t be trusted to regulate themselves and must be held fully accountable when they fail to limit harms, says Rick Claypool, a research director at consumer advocacy non-profit Public Citizen.

“Where existing laws and regulations already apply, they must be rigorously enforced,” he said in a statement. “Where there are gaps, Congress must act to put an end to businesses that exploit young and vulnerable users with addictive and abusive chatbots.”

• In the US, you can call or text the National Suicide Prevention Lifeline on 988, chat on 988lifeline.org, or text HOME to 741741 to connect with a crisis counselor. In the UK, the youth suicide charity Papyrus can be contacted on 0800 068 4141 or email [email protected], and in the UK and Ireland Samaritans can be contacted on freephone 116 123, or email [email protected] or [email protected]. In Australia, the crisis support service Lifeline is 13 11 14. Other international helplines can be found at befrienders.org

Requirements for gardens and the planting of trees must be included in Labour’s planned new rules for housebuilders, green groups have said.

The government is drawing up its future homes standard for new developments and it is not yet clear what requirements there will be for green space.

Developers are currently subject to biodiversity net gain rules that mean they have to ensure there are more spaces for nature after a development is built than before construction commenced.

Gardening groups including the Royal Horticultural Society (RHS) are now asking for rights to green spaces to be enshrined in the plans to boost housebuilding. Prof Alistair Griffiths, the RHS director of science, pointed to a study based on UK Biobank data that showed people with gardens tend to have lower mortality risks, lead healthier lives and be less stressed.

“If you have more green space or a garden, you will do more physical exercise and be more likely to meet NHS guidelines for physical exercise. One of the greatest challenges the government faces in terms of the health service is levels of obesity, so this is significant,” he said.

Clare Matterson, the RHS director general, said that including gardens with the 1.5m homes that the government has pledged to build could save the NHS money.

“Let’s completely flip back around and make sure the outside space is actually thought about as much as the inside space. It has so many benefits, cost-saving benefits, particularly to the NHS,” she said.

She added that homes on the market should have a garden performance certificate, like they have for insulation, to indicate the quality of the soil, the amount of water it stores, and the biodiversity.

“When you buy a house you get an energy performance certificate, you have ratings for all the white goods in the kitchen. How about having a garden performance certificate?

“Let’s allow people to make some really important choices and give an incentive for people who are selling homes to create really good gardens.”

Developers often plan to include gardens and green space but overspend on the construction of the homes and put concrete where plants should be. Wayne Grills, the chief executive of the British Association of Landscape Industries, urged Labour to include gardens in its plans.

“We can actually be in there advising the contractors that are there at the same time that construction is going on, rather than being allowed to come back and dig up that same piece of environment,” he said.

“And the second thing for me [is] making sure that the budget is there. So we certainly see some really good, specified schemes, but very often the building is overspent over time and then landscaping that goes around it is cut back in many cases.”

Griffiths said that in the medium-term future, the UK would have a climate much like that of Barcelona now, and would need more planting.

“If you look at car parks and if you look at housing estates and developments in this country, there are no trees and there is no shade. This is not the case in France, Barcelona [north-eastern Spain] and other countries, they have spaces designed for urban cooling,” he said.

A spokesperson for the Ministry of Housing, Communities and Local Government said: “The government recognises the importance of building high-quality housing, and our planning reforms set clear expectations to ensure new developments meet the standards required.

“This includes taking into account the national model design code, which makes clear that open spaces, including private outdoor spaces, contribute to the quality of a place and to people’s quality of life.”

Turkey’s interior minister has blamed a “terrorist attack” for an explosion and assault at the headquarters of the national aerospace company, Tusaş, outside Ankara that has killed four people and wounded 14 others.

The large blast happened outside the building at 4pm on Wednesday, and there were reports that gunfire was also heard in the vicinity.

Turkey’s president, Recep Tayyip Erdoğan, said: “We have four martyrs. We have 14 wounded. I condemn this heinous terrorist attack and wish mercy on our martyrs.”

The interior minister, Ali Yerlikaya, said: “A terrorist attack was carried out against the Tusaş facilities in Kahramankazan, Ankara. Unfortunately, we have martyrs and injured people.”

He said two attackers – a woman and a man – had been “neutralised” and work was under way to determine their identities. Yerlikaya did not say whether there were any other attackers still at large, amid conflicting reports of whether the situation was ongoing.

Media outlets that had been showing live footage from the scene were forced to halt their broadcasts after Turkey’s media watchdog ordered a blackout of images from the site. Habertürk TV said earlier there was an ongoing “hostage situation”, without giving further details.

The exact circumstances of the explosion and subsequent gunfire remained unclear, with some media reports suggesting it was a suicide attack.

It was not clear who was behind the attack. Kurdish militants, Islamic State and leftist extremists have carried out attacks in the country in the past.

Erdoğan was in the Russian city of Kazan for a Brics summit of major emerging market nations, including Brazil, Russia, India, China and South Africa, where he held talks with Vladimir Putin.

According to initial reports, the attack was launched by several gunmen who arrived at the site by taxi. Local television footage appeared to show individuals wearing black and carrying rucksacks in the streets near the building firing at bystanders. TV images also showed a damaged gate and a clash in a car park.

The TV channel NTV said a group of assailants arrived at an entrance to the complex in a taxi during a changing of the security personnel. At least one of the assailants detonated a bomb, while other attackers managed to enter the complex, it said.

Tusaş is one of Turkey’s most important defence and aviation companies. It produces Kaan, the country’s first national combat aircraft, among other projects.

According to the Turkish newspaper Hürriyet, staff in the building were directed to shelters for security reasons.

The blast occurred as an important trade fair for the defence and aerospace industries was taking place in Istanbul, which was visited this week by Ukraine’s top diplomat.

Turkey’s defence sector, which is known for making Bayraktar drones, accounts for nearly 80% of the country’s export revenues, with revenues thought to exceed $10.2bn in 2023.

The attack drew condemnation from the transport minister, Abdulkadir Uraloğlu, and the opposition leader, Özgür Özel, who heads the Republican People’s party (CHP). “I condemn the terrorist attack against TAI facilities in Kahramankazan … I condemn terrorism, no matter who or where it comes from,” Özel wrote on X.

The Nato secretary general, Mark Rutte, said the military alliance would stand with Turkey. He posted on X: “Deeply concerning reports of dead and wounded in Ankara. #NATO stands with our Ally #Turkey. We strongly condemn terrorism in all its forms and are monitoring developments closely.”

In January two gunmen opened fire inside a Catholic church in Istanbul, killing a man, with Islamic State claiming responsibility.

The dangers of a collapse of the main Atlantic Ocean circulation, known as Amoc, have been “greatly underestimated” and would have devastating and irreversible impacts, according to an open letter released at the weekend by 44 experts from 15 countries. One of the signatories, Stefan Rahmstorf, an oceanographer and climatologist who heads the Earth system analysis department at the Potsdam Institute for Climate Impact Research in Germany, explains here why he has recently upgraded his risk assessment of an Amoc breakdown as a result of global heating – and what that means for Britain, Europe and the wider world.

What is Amoc?

Amoc, or the Atlantic meridional overturning circulation, is a system of ocean currents that brings heat into the northern Atlantic. Warm surface water from the tropics flows north and releases its heat in the subpolar Atlantic, south of Greenland and west of Britain and Ireland. Then it cools and sinks to a depth of between 2,000m to 3,000 metres before returning south as a cold current. Amoc is one of our planet’s largest heat transport systems, moving the equivalent of 50 times the human energy use, and it has a particularly strong impact on the climate in Europe, affects the ocean’s CO₂ uptake and oxygen supply, as well as rainfall patterns in the tropics.

How is Amoc different to the Gulf Stream?

They are connected because the northwards flow of Amoc goes via the Gulf Stream, which is a warm and swift Atlantic Ocean current that originates in the Gulf of Mexico, then flows through the Florida straits, up the coast of the US and then across towards Europe. Amoc contributes just 20% to the Gulf Stream water flow but most of the heat transport, since Amoc’s deep return flow is very cold. It works like a central heating system.

What is happening to Amoc?

There are indications that Amoc has been slowing down for the last 60 or 70 years due to global heating. The most ominous sign is the cold blob over the northern Atlantic. The region is the only place in the world that has cooled in the past 20 years or so, while everywhere else on the planet has warmed – a sign of reduced heat transport into that region, exactly what climate computer models have predicted in response to Amoc slowing as a result of greenhouse gas emissions.

Are there other indications that Amoc is weakening?

Yes. There is a region of excessive heating along the east coast of North America, which is predicted by climate models and oceanographic theory as a result of a slowing Amoc, which pushes the Gulf Stream closer to the shore.

Another indicator is a reduction in the salt content of seawater. In the cold blob region, salinity is at its lowest level since measurements began 120 years ago. This is probably linked to Amoc slowing down and bringing less salty water and heat from the subtropics.

Why is the salt content significant?

When the water is less salty, it is less dense, which makes it harder to sink down. That is important because the sinking process is what drives Amoc. The fresher the water, the slower it gets.

What is driving the change in salinity?

Firstly, salinity is directly affected by global heating, which enhances the water cycle so there is more evaporation in the subtropics and more precipitation in the subpolar oceans. This leads to a freshening of the subpolar ocean. Then there are additional contributions from the melting of sea ice and the loss of continental ice from the Greenland ice sheet, which is freshwater that flows into the ocean.

It is an amplifying feedback: as Amoc gets weaker, the subpolar oceans gets less salty, and as the oceans gets less salty then Amoc gets weaker. At a certain point this becomes a vicious circle which continues by itself until Amoc has died, even if we stop pushing the system with further emissions.

When might Amoc weakening reach a point of no return?

The big unknown here – the billion-dollar question – is how far away this tipping point is. It is very difficult to answer because the process is non-linear and would be triggered by subtle differences in salinity, which in turn depend on amounts of rainfall and cloud cover over the ocean as well as Greenland melting rates. These are hard to model accurately in computers so there is a big uncertainty relating to when the tipping point will be reached.

What is the range of forecasts?

Until a few years ago, the general thinking in the Intergovernmental Panel on Climate Change (IPCC) was that the probability of crossing the tipping point this century was less than 10%. Since then, there have been a number of studies suggesting a collapse would probably be triggered this century, possibly in the next few decades. So my risk assessment has really changed. I am now very concerned that we may push Amoc over this tipping point in the next decades. If you ask me my gut feeling, I would say the risk that we cross the tipping point this century is about 50/50.

Is there any possibility it has already happened?

I wouldn’t rule it out completely, because it would be very hard to tell from observations. Nothing dramatic happens at the tipping point. That just means Amoc is then doomed and it will slowly die, but that process could take 50 to 100 years. Because the Amoc is already weakening we can’t be entirely sure whether we already passed a tipping point, but I would say this is most likely not the case, so it is not too late to prevent this.

What would be the warning signs of Amoc collapse?

We need to keep monitoring the flow of water in the Atlantic, which is being done with the Rapid project. We should also monitor deep winter mixing in the northern Atlantic and Nordic seas. If the deep mixing starts to decline a lot, that could be an early indicator that we are approaching a tipping point. There are some signs of this, but we don’t have enough data yet to be sure.

What would be the consequences of Amoc breakdown?

This has happened repeatedly in Earth’s history, most recently during the last ice age, when big ice masses slid into the ocean – so-called Heinrich events – adding meltwater that diluted the salinity of the north Atlantic. These are among the most massive upheavals of climate conditions in Earth’s history.

The effects include a cooling of the northern hemisphere, particularly northwestern Europe. There would also be a shift of the tropical rainfall belt to the south, which is bad because the rains will move away from the rainforests to regions that are not used to so much rainfall. So this will mean droughts in some regions and floods in others.

Amoc collapse would also have a major impact on the northern Atlantic sea level, which would rise by half a metre or so, in addition to the rise caused by global heating. It would also reduce the CO₂ uptake of the ocean because Amoc sinking in the northern Atlantic takes a lot of CO₂ down into the deep oceans where it is safely locked away from the atmosphere.

Amoc collapse would also change the nutrient supply and reduce the oxygen of the deep oceans. This would have a massive effect on marine biology and the entire ecosystem of the northern Atlantic.

Many of these things are happening already, aren’t they?

Yes, to some extent. This is partly because Amoc is weakening and so is its counterpart in the southern hemisphere, the Antarctic bottom water formation, according to research by Australian colleagues.

Could the cooling effect of Amoc collapse offset the heating caused by human emissions?

I can’t think of anywhere that will be better off. If it were just a case of averages, then somewhere like Germany might see a balance. But weather is not a climate average; it is seasonal and highly variable. Within the average you can get warm air from the south or cold polar air outbreaks from the north. These contrasts will be more pronounced if Scandinavia and Britain cool while Spain and Italy warm. This will drive much greater variability in the weather, which is bad for agriculture, and it will cause more storms. I would expect major extreme weather events that we have not seen in the past.

The key thing about climate change is that both the ecosystem of the Earth as well as human settlements and infrastructures are highly adapted to what the climate was like in previous centuries. So any change – whether global heating or global cooling – will always be bad because it will lead to maladaptation. Think of the tremendous flooding we have seen somewhere in the world almost every week in the last months. If it had been like that for centuries, then river and sewer systems would be adapted to take up that water. But because we are not used to that, there are disasters. That is the problem of climate change.

How certain is the science about Amoc collapse?

It is well established that Amoc is weakening and that a tipping point exists. The uncertainty is about when we will cross that threshold. We also have very few studies about what the combined effect of Amoc collapse and global heating would exactly look like.

It is a question of risk assessment. I compare it to being told that there is a 10% chance of an airplane crashing. Would you get on that plane? I wouldn’t. The disastrous consequences are unacceptable.

Why haven’t the IPCC made more of Amoc risks?

They have not done enough risk assessment because they tend to focus on the most probable scenarios for future climate change. Some colleagues say we shouldn’t talk about extreme possibilities like an Amoc collapse because it sounds alarmist and might distract people from more certain impacts of global heating, which are bad enough. But I think those extreme risks are part of the whole picture that we need to consider, to make responsible and rational decisions.

How long would an Amoc collapse last and how survivable would it be?

The last time, it took about 1,000 years to recover, though the past is not a direct analogue because there is also massive CO₂ forcing this time – CO₂ is already higher than any time in 15m years. There are physical reasons why some form of deep overturning circulation will eventually come back.

One thing is for sure: humanity will not die out. But for some countries that will be in the midst of this, like Norway, and Scotland, the risks will be existential and raise the question whether people can continue to live there or whether most of them would rather move.

How does the Amoc threat compare to other climate tipping points?

That is hard to tell. It is a trade-off between more distant futures and things that are already happening.

We have already crossed the tipping point of many coral reefs, which are now in middle of global die-off. This is very depressing because it is already too late to do anything about it, though marine biologists have warned about the risks for a long time. The Amazon rainforest is also dangerously close to a tipping point. As we speak, it is going through the worst drought on record.

Then in the very long run, we have the ice sheet tipping points in Greenland and west Antarctica. From Greenland alone, this will lead to a seven-metre global sea level rise that will wipe all major coastal cities off the map. But that will occur over many centuries because ice sheet melt is a slow process.

Amoc is on an intermediate timescale because it unfolds over decades to 100 years.

I am worried about all of these things to be honest. And the conclusion for all of them is the same: this is all driven mainly by fossil fuel emissions and also deforestation, so both must be stopped. We must stick to the Paris agreement and limit global heating as close to 1.5C as possible. I don’t think it is my job to talk about my feelings, but I do have two children and I am very worried about what future they will live in. I sometimes joke that physicists don’t have feelings. But even physicists care about their kids.

On a misty winter morning, farmer Mohit Chutia sits on the ground outside his home rocking his grandson in his lap. He sings about the hoolock gibbons, the only ape species in India. High in the tree canopy above, the gibbons leap gracefully from branch to branch. Below, Chutia and his family watch.

It is a picture of the coexistence that has endured for generations between the endangered gibbons and villagers in Barekuri in Assam, in the remote east of the country.

“They are like my own children,” says Chutia. His close bond with the gibbons has prompted other villagers to call him bandar – monkey.

The hoolock gibbon is found only in a few places in the world and estimates of total numbers are uncertain. It was once thought India had about 12,000, but in 2017 experts revised this down to between 5,000 and 10,000.

In Barekuri, a tiny pocket of about 19 gibbons is left – and only four are females, placing the group at the edge of viable survival. Close up, the gibbons are a vision of tight, respectful coexistence with humans – but looming in the background are the wider threats of pollution, extractive industries and deforestation driven by human activity.

A new Guardian documentary – Guardians of the Gibbons – looks at how Chutia’s community has created an unusually close bond with their ape neighbours.

On the drive towards Chutia’s home, in a remaining patch of jungle, the vast and famous tea estates of Assam stretch out across the horizon on both sides of the road. Turning off the road for Barekuri, the landscape suddenly changes to thick forest and dense undergrowth.

The canopy used to be so thick that villagers would hear the hoolocks’ calls – a collection of whoops and hoots – but only caught glimpses of them. However, deforestation, mining for oil and gas, expansion of villages and roads, and the growth of monoculture crops such as tea have all fragmented the forest cover.

“For the gibbons, who are almost totally arboreal, it means they are cut off from areas of the forest, unable to cross the open areas created by the road and rail line. Their access to the fruit they depend on has been reduced,” says Ragini Nath, who made the documentary with fellow film-maker Chinmoy Sonowal.

Inside his brick-and-bamboo home, Chutia talks about his favourite gibbon, Twik, who nearly died from electrocution from a low-hanging wire. Within minutes of Chutia calling, Twik emerges from the tree canopy, his mother watching protectively from a few feet away.

It is not clear yet whether Twik is female – hoolock gibbons take years to develop the golden brown fur that marks a female of the species. If Twik is female, her ability to grow the species’ numbers could help this small population survive.

The tree canopy looks lush and thick but Chutia says there are not enough fruit trees. “The day I saw them eating leaves years ago, I realised they weren’t getting enough fruit. If they had had enough fruit, they would never have taken the bananas I offered them,” he says.

The story of humans and gibbons is not only one of peaceful coexistence, but also looming threats. As you drive through the forest, oil and gas rigs loom into view, flares burning.

The extraction business is booming in this region. Assam is a leading oil and gas producer: the state accounts for 14% of India’s crude oil production and 10% of its fossil gas. The state government estimates that 1.3bn tonnes of crude oil lies under the ground, more than half of which is unexplored.

Chutia has vivid memories of 2020, when a gas blow-out just over a mile away caused a fire that raged for months. It led to the deaths of three people and almost 26,000 animals, including two gibbons. “It felt like we were breathing oil,” says Chutia.

Ishika Ramakrishna, a researcher from Bengaluru who is studying gibbons for her doctorate at the Centre for Wildlife Studies, says: “It’s not just the trees that are felled for the mining but the fact that roads have to be widened to allow for large vehicles. Any disruption to the canopy, even minor, can severely affect the gibbons’ movement and survival.”

In a recent radio broadcast, prime minister Narendra Modi praised Barekuri’s coexistence with its hoolock gibbon population, which he said had “made their home in this village”. But the Assam state government, ruled by Modi’s Bharatiya Janata party, is considering a new oil and gas exploration project in Hollongapar gibbon sanctuary in Jorhat, just 110 miles from Barekuri.

To preserve the remaining gibbons, Ramakrishna wants the Assam government to stop all further mining activity in and around Barekuri, start planting trees to restore habitat and food resources, and explore “canopy bridges” as a solution to the breaks in the tree canopy.

At present, gibbons are either unable to cross wide open areas to reach another section of forest – or they do so using electrical lines, which can result in electric shocks, some of which are fatal.

“What we’re trying to do is consult the villagers to see what design would work best for the bridges, which would be made of bamboo. It would compensate for the break in canopy cover and allow the gibbons more access to the fruits they need to survive,” says Ramakrishna.