On the evening of 18 December 2009, Barack Obama and a trail of White House and State Department officials swept through a cavernous exhibition centre in Copenhagen and barged, uninvited, into a private meeting between the leaders of four powerful developing countries – China, India, Brazil and South Africa.

It was about 6pm on the final day of the Copenhagen climate summit, when nearly 200 countries were expected to agree on collective action to fight climate change. For the first time, the United Nations claimed, countries were on the verge of reducing the greenhouse gas emissions. Obama, along with dozens of other presidents and prime ministers, had flown into Copenhagen for the final day of the summit at the request of the UN secretary general, Ban Ki-Moon, who believed their presence would embolden negotiators to make a deal. The UN was so optimistic about the prospects at the start of that year that it signed off on an ad campaign touting “Hopenhagen”.

But by the time Obama gatecrashed the meeting of developing nation leaders, the sun had long set on the Bella Centre exhibition hall, and on any chances of a deal. Hopenhagen lay buried under two weeks of mistrust, rancour, sleep deprivation and unspeakable catering. As the US president saw it, the only chance to avoid a complete collapse of the summit was to try to come to an understanding with China – foremost, along with the US, of the world’s biggest polluters, and holding fast to its industrial progress.

It is hard even now to fully grasp the degree of dysfunction that took hold of the conference. Some delegates still say, only half-jokingly, that the experience left them with PTSD. Even the summit’s hosts were at war. The Danish prime minister, Lars Løkke Rasmussen, tried to sideline the climate minister, Connie Hedegaard, who had spent months immersed in preparations for the summit. His office prepared a secret draft text that was shared with a small group of delegates – not, as convention demanded, with all of the countries at the meeting. The Chinese felt scorned because their deputy premier was left off the list for a reception at Christiansborg Palace and kept waiting in the cold by intense security around the conference venue. The Americans felt slighted because they were unable to secure a second private meeting with the Chinese. The leaders of 130 developing countries accused rich countries of plotting to cut them out of negotiations. Well after midnight, in the final hours of the closing plenary, Claudia Salerno, the Venezuelan negotiator, was so incensed by the entire process that she banged her hand on the table until it bled. “This hand, which is bleeding now, wants to speak,” she said, showing her bloodied palm to stunned onlookers.

“It was a very confusing situation for everybody involved,” said Giza Gaspar Martins, a diplomat from Angola. “My first meeting took place at three o’clock in the morning,” he said. “We were clueless at Copenhagen.”

The Danes, who had planned for 15,000 people to turn up, were completely overwhelmed when 35,000 delegates and observers tried to get into the Bella Centre. Campaigners, journalists and high-level negotiators reported spending up to eight hours standing in crowds outside the metal gates, while a rare pre-Christmas cold spell dumped 10cm of snow on the city. In her memoir Hard Choices, Hillary Clinton describes waiting to exit the hall in a queue of VIP limousines that moved so slowly that the French president, Nicolas Sarkozy, rolled his eyes and moaned, in English: “I want to die!” When Obama finally arrived, Clinton told him it was the most chaotic event she had attended since her eighth-grade student council elections. Inside the hall, negotiators were getting too little food and almost no sleep. Unable to eat any more cold, limp sandwiches, US officials on the ground begged White House staffers coming in from Washington on Air Force One to bring in microwaveable bags of green vegetables.

By the time the leaders of China, India, South Africa and Brazil gathered in the upstairs office suite, the first order of business – unofficially – was how to avoid responsibility for the Copenhagen summit’s collapse. None of the countries wanted to take the blame for getting in the way of the deal that would save the world. The discussions were just getting started when the officials caught sight of Obama through the plate glass door. “Oh, so this is where you guys are holed up,” the president said, stepping into the room.

Six years later, countries are poised to gather once again in an effort to reach a deal to halt climate change. Next week’s meeting in Paris, taking place in a sombre atmosphere following the horror of the Isis attacks, will be the 21st annual UN climate summit. In the acronym-studded and obfuscatory language that surrounds these events, the Paris meeting will be the 21st Conference of the Parties (CoP) of the United Nations Framework Convention on Climate Change (UNFCCC). The pressure to reach an accord is higher than ever.

Negotiators, in hopeful mood, describe Paris as the anti-Copenhagen, ticking off the ways in which countries are better prepared this time around. Nations have set their reduction targets in advance. The US has worked to reach separate deals with China, India, Brazil and other countries. Negotiators have whittled down the text of the proposed agreement to a manageable length. The French hosts have invited the leaders for the start of the summit, not the end, which will leave negotiators time to work on the deal. But optimism is evanescent: in a negotiation involving nearly 200 countries, when all of the hard choices are left until the end, anything can happen. For a reporter, the experience is slightly horrifying. The meetings, with their increasing numbers of camp followers and dozens of side events, bear almost no resemblance to the usual buttoned-up affairs of global summitry. But in the final three or four days, the carnival tails off, and real power is wielded behind closed doors, in the negotiating rooms.

The future of the planet has been argued over point by point over long periods, but agreements are made in a sudden burst of activity at the last possible moment, by lawyers and bureaucrats who have not slept or eaten properly in days. No summit is allowed to end in failure: negotiators do not get their planes home until they cobble together a form of words that can be passed off as a result. Accordingly, summits have produced a slurry of declarations, accords, agreements, action plans, and protocols. The climate circus would be farcical, if the fate of billions were not at stake.

In the highly scripted world of international negotiations, an unannounced and uninvited visitor – even if he is the leader of the free world – is a massive breach of protocol. The representatives around the table in 2009 were momentarily flummoxed, and there were a few tense exchanges between security details before the then Chinese premier, Wen Jiabao, made a motion of welcome with his hands, and Obama entered the room.

Barack Obama’s attendance at the Copenhagen summit in 2009 raised enormous expectations that he would reverse the climate policies of his predecessor, George W Bush. Photograph: Axel Schmidt/AFP/Getty Images

The president draped an arm around the then Brazilian leader, Luiz Inácio Lula da Silva, and said: “I want to sit next to my good friend, Lula,” according to the accounts of those in the room. “Right from the moment he entered, it wasn’t as if he was groping around. He got right in there,” said Chandrashekhar Dasgupta, one of the key Indian negotiators at the talks. “He exuded confidence. He didn’t give an impression of being tense or anything of that sort.”

Obama had been in the White House for just 11 months – and there were enormous expectations that he would reverse the climate policies of his predecessor, George W Bush. Bush notoriously withdrew the US from the Kyoto protocol, killing off the 1997 agreement to reduce global emissions. Obama, meanwhile, had campaigned for election promising to save “a planet in peril”. A week earlier, the Nobel committee had awarded Obama the peace prize, in recognition of the possibilities of his presidency. The trench warfare with Republicans over healthcare, immigration and gun violence that were to scar the duration of his presidency still lay ahead. His hair barely showed any grey.

A Brazilian minister gave up his place, and Obama took a seat at the table next to Da Silva and directly opposite Wen. As the president settled in, he dropped the show of jocularity, and turned to the Chinese leader to ask, with some annoyance: “Mr Premier, are you ready to see me? Are you ready?”

China and the US are considered by many to be the supervillains of climate change, nations whose economic rise was accomplished only by putting the planet in peril. The US, once the world’s biggest polluter, lost that title to China in 2007. By 2009, the majority of the nearly 200 countries in the world agreed that because of their industrial history, the US, Europe and Japan had a greater duty to curb emissions. That position was codified in the Kyoto protocol. In Obama’s view, China also needed urgently to curb its pollution levels. His reasons were the sheer scale of emissions from China’s coal-fuelled factories, and a need to mollify American public opinion. Republicans in Congress, who mostly deny the reality of climate change, were using China as an excuse not to address the US’s own dependency on coal and oil.

Obama turned to the Chinese leader to ask, with some annoyance: 'Mr Premier, are you ready to see me? Are you ready?'

In the 45 or so minutes of ensuing conversation – punctuated by a couple of screaming matches in Mandarin between members of the Chinese delegation that were not translated – the world’s biggest carbon polluters, for the first time in history, agreed on a common goal.

In truth, it was not much of a goal. But it was the only way to salvage the disastrous negotiation, and it did set out the few points on which the US and China – along with the other big developing countries – agreed. The two-and-half-page text “recognised the scientific view” that warming must be limited to a global average of 2C above preindustrial levels in order for there to be a reasonable chance of avoiding catastrophic climate change. For the first time, the more powerful developing countries and the industrialised countries agreed on the need to cut emissions. Rich countries pledged that they would help rustle up $100bn a year in public and private funds by 2020 for developing countries to switch to cleaner forms of power, and to finance a Green Climate Fund to allocate the money. The agreement was seriously flawed. It omitted a target date for peaking emissions, which meant there was no clear way of getting to the 2C goal, and it did not propose any penalties for climate laggards.

As the meeting in the conference room came to a close, Obama turned to Wen and asked: “Do you agree?” Wen nodded his assent without speaking.

At about 11pm Obama told a press conference the leaders had reached a “meaningful and unprecedented breakthrough”. “I believe what we have achieved in Copenhagen will not be the end, but rather the beginning of a new era of international action,” he said. “We are in this together.”

The president, racing to get home to Washington ahead of a severe blizzard that was bearing down on the east coast of the US, immediately decamped for the airport. But the storm he left behind was just as big. Most of the delegates had no idea that there was a deal until they saw Obama’s televised press conference on the closed-circuit television at the Bella Centre. In any case, under UN rules, a decision by five major economies – even if they did account for a majority of global emissions – simply did not count. The rules for the climate talks demanded consensus. “The moment he said there was a deal, everybody’s backs got put to the wall,” said Jairam Ramesh, who was then India’s environment minister. “They all said: ‘What is this? How can an agreement between four heads of state and the US be taken as a decision of 193 countries?”

It was 3am before the Danish hosts asked other countries what they thought of the deal. In the vast hall on the ground floor of the Bella Centre, Lumumba Di-Aping, the leader of the G77 group of the world’s 130 poorest countries, denounced “a suicide pact, an incineration pact in order to maintain the economic dominance of a few countries”. The conference sputtered to a close, withholding formal approval of the proposals worked out by Obama and the other leaders.

By the time Obama landed at Andrews Air Force, the storm was in full fury, and the summit was being written off as a failure. The US continued to claim Copenhagen as a breakthrough, but for many developing countries, the agreement was cast as a betrayal: the moment when the industrialised world tried to shrug off its obligations. For the small island states of the Pacific, which face being inundated by rising seas, the summit was a profound disappointment.

In June 1992, Bikenibeu Paeniu, the prime minister of the tiny Pacific island of Tuvalu, addressed a press conference on the sidelines of the Rio de Janeiro Earth summit. More journalists sought accreditation to cover that event than had covered the first Gulf war a few months earlier.

“I come to Rio to tell you of the fate of my people,” Paeniu began, pleading for an agreement that would set firm targets and time frames for cutting emissions. He made a direct appeal to then president George HW Bush, who did not want to commit to a deal. “He has a moral and spiritual obligation to face reality and accord what is right for the people of the world,” Paeniu said. “And if he doesn’t?” he was asked. “There is someone up there who will judge us,” Paeniu said. “We will all be judged. Even President Bush.”

Tuvalu’s remarks were broadcast widely, and Bush reluctantly agreed to a watered down version of the treaty.

The Rio Earth summit in 1992. Photograph: Sipa Press/REX Shutterstock

Since 1992, negotiators have gathered every year to turn that weak promise into concrete action, meeting in cities including Berlin, Kyoto, Buenos Aires, Marrakesh, New Delhi, Milan, back to Buenos Aires, Montreal, Nairobi, Bali, Copenhagen, Doha, and Lima. The annual gatherings have grown from roughly 500 participants at the first official climate negotiations in Berlin in 1995 to sprawling jamborees – gargantuan rotating festivals of anything remotely associated with environmental causes or, increasingly, profit-making “green” enterprises. The talks are conducted in English. Inside dimly lit halls, negotiators have spent two weeks at a stretch gazing at text blown-up into headline size by overhead projectors, doing battle over “shall” or “should”, “commitment” or “contribution”.

“The day can go on and on and on and on,” said one former delegate. “You need to be very sharp. Even being in a windowless room with the lights down and a projector on the wall and talking about moving a comma around – you need to be alert, because it is significant.”

It also helps to be resourceful. “You eat what you kill basically, because negotiations go 24/7 but the concession stands do not,” the delegate said. “It is literally people stockpiling rations and the smart people, the negotiators who have been around the block many times, bring their own food and know how to pack appropriately. They can be completely autonomous.” Several people complained that the food situation is even worse for vegetarians. One observer, who has never missed a meeting, lost 15lb during the Kyoto meeting, when the vending machines ran out of food.

Old timers say they make a point of carrying protein bars, nuts, and dark chocolate – and grabbing sleep when they can get it. I was told that if you don’t sleep in the first week, then you’ll have no judgment left.

In the conference halls and the streets around them, the summits tend to be sheer pandemonium: activists arrive smeared in green paint or sweating behind furry polar bear suits; peasant women from the Andes in traditional bowler hats sing songs to Mother Earth when their leaders are on camera; celebrities bring their own circus – Robert Redford is expected to come to Paris and Thom Yorke is a conference regular. Campaign groups throw together mass demonstrations and expert briefings, organise daily mock prize givings such as the Fossil of the Day award, and the semi-stalking of delegates, known as Adopt a Negotiator. When the climate negotiations came to Warsaw in 2013, the World Coal Association organised a competing conference with the support of the Polish economics ministry, which was disrupted by climate activists waving an eight-metre inflatable pink lung. There is always at least one spectacular stunt, such as last year’s disastrously ill-thought out move by Greenpeace to drape large yellow letters spelling out “Time for Change” over the Nazca lines in the Peruvian desert. The campaign group was later forced to apologise for disturbing the ancient heritage site.

Before the attacks, the French government expected more than 45,000 participants from 196 countries at the 30 November summit, including 25,000 delegates and official observers. The remaining 20,000 participants included activists, journalists, politicians, academics and business leaders. Those numbers could now shrink as marches and other events are cancelled owing to security concerns.

For old hands at the negotiations, such as Yvo de Boer, a former Dutch civil servant and UN climate chief known for his trenchant views, the conferences have become trapped in an endless cycle of repeats. “The CoPs actually remind me a lot of Peyton Place and As the World Turns – in the sense that every episode is really exciting, but if you don’t watch for three years, you haven’t missed anything,” De Boer said.

Kyoto protocol negotiators were told to clear out because the venue was booked for a lingerie show

Each of those annual gatherings produced its particular dramas. Negotiators for CoP 3 which produced the Kyoto protocol were told to clear out before they were entirely finished because the venue was booked for a lingerie show. CoP 6, held in the Hague, ran so badly over time that the UN was reduced to convening an additional conference a few months later, just to conclude the proceedings. CoP 15 or Copenhagen was the deal that got away.

Some years – as in the run-up to the Copenhagen meeting in 2009 and this year – there can be as many as four or five additional meetings. Negotiators, and their followers, can easily find themselves on the road for up to eight weeks out of the year. “There have been people who met each other in the process and got married. There were a number of people who met each other in the process who got married – and divorced from other people as a consequence. You did regularly hear stories of marriages breaking down because of people spending so much time in the negotiations. And you lost people along the way. People died. There were colleagues who were lost at the time of the tsunami in Thailand [in 2004],” De Boer said.

“It does get to be a bit of an atmosphere of an extended family of people who have this process in common that is such a major part of their life – and yet almost incomprehensible to the outside world.”

Like all family gatherings, things can get emotional. In 2007, De Boer, then UN climate chief, broke down in tears at the Bali summit. By the time of the failed Copenhagen meeting two years later, he was done with climate negotiations.

Last July, during an informal session for negotiators hosted by the French government, Todd Stern, the State Department climate change envoy, found himself sitting unusually close to his Cuban equivalent. (Countries were seated in alphabetical order in French, putting les Etats Unis very near its old adversary.) Three months later, Stern was holding a conference call with reporters on a scratchy phone line from Havana. As he explained it, the US approach to Cuba was a product of that chance seating. “I started talking to my Cuban counterpart, and then we had a bilateral at the end of the meeting,” Stern said. “I kind of had it in mind from that time on to come here.” Stern talked about climate change and trying to persuade Cuba to look positively on the US vision for a deal in Paris, but he also suggested that the talks were not limited to environmental issues.

Veterans describe negotiations as an elaborate game, in which the competing demands of nearly 200 countries are juggled. Some of the trade-offs occur around the negotiating table, but not all.

A protester in a polar bear costume at the Cancun summit in 2010. Photograph: Ronaldo Schemidt/AFP/Getty Images

“It really is like playing chess on 15 different chess boards at the same time,” De Boer said. “If you give vulnerable countries something, then you have to give oil-producing countries something, and somewhere else you have to give countries with a strong private sector something, and somewhere else you have to give eastern European countries that had an economic collapse after the cold war something. There can be 20 people spinning in place at the same time.”

In the early years, climate change was seen as a self-contained environment problem – something that could be sorted out with scrubbers or smokestacks or other standard pollution remedies. That had worked in the recent past. In 1987, countries agreed on a treaty to fix the hole in the ozone layer; in 1991, the US and Canada reached a deal to reduce acid rain. But climate change required a much bigger fix. It was a global problem, an existential threat, with sweeping economic implications. It seems evident now that the changes required to halt, and eventually, reduce greenhouse gas emissions would require a transformation of the economy. But climate experts say that was not the case in the 1990s, when the negotiations first got under way.

“We didn’t understand the nature of the threat well enough. We didn’t have enough experience of climate change happening. The science was not clear enough at the beginning,” said Tom Burke, a long-time campaigner who was at the summit. Burke went on to advise three UK environment secretaries before founding the E3G thinktank. In his view, there was a necessary learning process in dealing with climate change – although inevitably it took much too long.

Other difficulties were surreptitiously injected into the negotiation process by Washington lobbyists, working for Saudi Arabia and Kuwait, as well as US oil and coal companies. Industry-funded front groups such as the Global Climate Coalition and the Global Climate Council commissioned scientists to produce reports that muddied the facts about climate change. They also dispatched to the talks lobbyists who sat with Saudi and Kuwaiti diplomats and reviewed the text, according to accounts by green-energy entrepreneur and writer Jeremy Leggett, and others who witnessed such meetings.

Following the lobbyists’ instructions, negotiators inserted language that linked climate aid for small island countries that could disappear entirely under rising seas to compensation packages for oil producers facing declining revenues. The coupling made it virtually impossible to establish rescue plans for the countries that needed them the most, without also diverting cash to petrostates. This idea infuriated the US and other rich countries. Lobbyists also managed to slow down negotiations by blocking a decision on voting rules, forcing negotiators to operate through the unwieldy mechanism of consensus.

The complexity of those negotiations gave rise to another debilitating tradition: putting off the difficult choices for another meeting, another year. The entire structure of the negotiations encouraged cliff-hanger meetings, with delegates refusing until the very last moment to give ground. “They have been known to spend the first two days of a five-day meeting disagreeing about the agenda,” remarked an observer from Bangladesh. The problem with the cliffhanger tactic was that the greatest source of discord remained as hot and raw as it had been at the start: which countries should take the blame for destroying the climate, and which countries should pay for trying to put it right.

For much of the 13 hours Obama spent on Danish soil, visiting the climate conference in 2009, Bernarditas de Castro Muller was huddled with a delegation of negotiators from Sudan, poring over the text about climate finance. Muller, a former Philippines diplomat now based in Geneva, has been a fixture at the climate negotiations for years, first on behalf of the G77 group, and latterly Sudan. Some of the G77 nations need financial support from the UN even to afford to send delegates to the talks. Other countries, especially the small island states, bring in negotiators. The Maldives hired the British writer and activist, Mark Lynas. Tuvalu hired an Australian campaigner, Ian Fry.

Muller did not expect to lay eyes on Obama. She knew he would be focused on the bigger powers, especially China. “Obama didn’t care about anybody else at the time,” Muller recalled. But, she said: “We knew something was cooking.”

Obama’s mission was, in fact, to break down the convention that the US, Europe and Japan should shoulder the main burden for cutting greenhouse gas emissions, and spread the obligation to richer developing countries such as China, India and Brazil, which were already beginning to outpollute the west when it came climate-altering gases.

Muller saw it as her mission, then and now, to keep the pressure on rich countries to reduce emissions. Our conversation took place over Skype in early November, the morning after she had returned to her base from a negotiation in Zambia. Muller began by pointing out that Africa and the small islands of the Pacific could be devastated, or disappear entirely, even if countries meet the 2C goal. As she spoke, she banged her hand on the table to make her point. (In negotiations, Muller has the reputation of being able to hold forth for 45 minutes at a stretch, which almost puts her in Fidel Castro’s class.)

The Lima climate change summit in 2014. Photograph: Eitan Abramovich/AFP/Getty Images

“Who cares? Bang! Does anyone care about these countries? Bang!” Muller asked, hitting the table to punctuate each sentence. “Climate change aid is not financing! Bang! It is not aid! Bang! It is not development assistance! Bang! It is not bilateral assistance! Bang! It is an obligation! Bang!”

Improbable as it seemed at the time, the whisper of a deal that was worked out around the table between Obama and developing countries at Copenhagen was the first step in breaching that divide. In the spring of 2014, Obama sent a letter to China’s president, Xi Jinping, proposing a joint approach on climate change. By that point, the US and China had been meeting quietly on climate for years, with the US sending two secret delegations to China when George Bush was in the White House. In early 2014, when John Kerry, the secretary of state, was on a visit to Beijing, he got the impression that China was ready to move. He suggested that Obama make a personal appeal to the Chinese leader. The gesture was returned. That November, at a meeting in Beijing of leaders of Pacific Rim countries, Xi invited Obama for dinner at his official residence in the leadership compound, next to the Forbidden City.

The next morning, the two leaders held a press conference to announce that their countries would move jointly to cut emissions. Obama said the US would aim to reduce emissions by up to 28% on 2005 levels by 2025 – or about double the pace of reduction in its current climate change plan. China committed for the first time to stop emissions from growing by 2030 and to get 20% of its power from non-fossil fuel sources – about the equivalent of two-thirds of the entire US electrical grid.

US officials were not so optimistic as to think that the partnership with China would automatically extend into the global negotiations, but at least the two countries were not active opponents. Brian Deese, a senior White House adviser, went so far as to venture that the US and China were now finally on the same team. The fault line between the industrialised and developing countries was blurred, though not erased. “For years and years and years there was a dynamic – particularly in negotiations – of the US and China being captains of the two different teams, and it was clear that was going to have to change in some way,” he said.

Teamwork was not immediately in evidence when the next conference took place in Lima, a month after the US-China breakthrough. On Friday night, the last of 10 scheduled days of talks, negotiators were still trying to choose between three options on almost all of the draft’s main issues. But the real divide, as ever, was about how to split the bill for fixing climate change. At nearly midnight, the Peruvian hosts sent the exhausted negotiators off to rest, hoping they would return in the morning willing to reach a compromise. When negotiators returned the next morning, the Malaysian delegate complained that he had been forced to cancel his flight to Cusco, sacrificing a life-long dream to visit Machu Picchu.

The talks continued for 12 more hours. The catering tents serving pisco sours and non-alcoholic chicha morada made from purple maize. A second midnight came and went, and then in the pre-dawn hours of Sunday morning, as a soft summer rain began to fall, negotiators emerged to declare the countries had managed to paper over their differences to sign a modest agreement. The solution came down to six words: “In light of different national circumstances”, a phrase that allowed rich and developing countries to avoid a hard decision about responsibilities. The formulation was used originally in the US-China agreement last November, Todd Stern, the state department climate envoy, told reporters at a 3am press conference. “I think the way we were able to deal with that issue in the US-China joint announcement actually ended up becoming quite significant here.”

On an unseasonably warm November morning, Christiana Figueres, the UN official charged with guiding countries towards a climate deal, visited Washington for one of her final rounds of meetings with US officials before the Paris climate talks. Figueres, a Costa Rican diplomat who is the daughter and sister of former presidents, has a brisk manner. On this morning, she was in a prickly mood, and made no effort to hide her impatience with her hosts, the main US nuclear lobby and the Christian Science Monitor, who had arranged her meeting with journalists in a basement conference room of the St Regis hotel. Figueres was coming straight from a breakfast meeting with Stern, in the hotel restaurant upstairs. “Let’s just cut to the chase,” she said, repeatedly interrupting the journalist introducing her, before abruptly tossing pages of prepared remarks to the floor. “There’s an emergency on climate. Let’s just cut to the chase,” she said.

By the standards of past summits, preparations for Paris were proceeding well. Countries were working together. Figueres was relentlessly upbeat. When Micronesia announced its climate plan, Figueres, as she has with virtually every other country, tweeted a message of thanks. When she flies into Paris for the summit this week, it will be her third visit since the start of November. The French government was sending Saudi Arabian envoys to India to get a deal. US officials including Stern were reaching out to climate negotiators from India to Indonesia, and Cuba to Canada. At their final negotiating round before Paris, countries managed to whittle the draft text down to a manageable 50 pages or so – albeit by preserving as many as four separate options on the most intractable questions, and putting off the hard choices for Paris.

But when asked whether Paris 2015 represented the last chance for countries to act on climate change, Figueres was unable to make any promises. She lashed out at those who, after more than 20 years of waiting for countries to act, would even dare to expect that Paris would bring some sort of conclusion.

“If you define successful as assuming that the Paris meeting is actually going to solve climate change, that it is going to be a one-off deal, then no,” she said. “If I have one person in Paris who says, ‘And you didn’t get down to 2C, then I will chop the head off of that person … I have been saying for at least a year that that is impossible.” Figueres insisted that after more than two decades of efforts – and of advancing climate change – a guarantee of a 2C world remained too ambitious an ask even in 2015. “You cannot turn around an economic development that we have been using, and some of us have been benefiting from, for 150 years in one year or even in 23 years,” she said. But if not now, then when? That was a question Figueres did not answer.

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• This article was amended on 30 November 2015. An earlier version said the then Danish climate minister, Connie Hedegaard, had spent a year before the 2009 Copenhagen summit preparing a secret draft text that was shared with a small group of delegates – not, as convention demanded, with all of the countries at the meeting. The draft was prepared by the prime minister’s office, not by Hedegaard.