BEIJING (BLOOMBERG) - The biggest emitter of planet-warming pollution managed to take almost the whole world by surprise.

In a September speech to the United Nations, Chinese President Xi Jinping put a 2060 end date on his country's contribution to global warming.

No other nation can do more to keep warming below the 1.5 deg C threshold set in the Paris Agreement.

Yet diplomats, climate activists, and even policy experts inside China for the most part had not anticipated this pivotal turnabout.

Just days before Mr Xi's UN appearance, in fact, European leaders including European Commission President Ursula von der Leyen and German Chancellor Angela Merkel had pressed him directly on a videoconference to follow the EU's example in setting a climate-neutrality goal.

Notes from the call reviewed by Bloomberg Green indicate that Mr Xi gave no hint he was about to abandon China's long-established policy against climate restrictions on economic growth.

Inside China, meanwhile, experts who specialise in the intricacies of emissions policy were stunned by Mr Xi's speech.

"Can this goal be achieved?" asked a bewildered post on WeChat from a retired climate negotiator in Beijing.

Most stakeholders with a hand in previous climate decisions had been kept out of the loop, according to interviews with more than a dozen industry groups, environmentalists, and government researchers in China.

But the decision to completely reorient a gigantic economy that's dominated by coal, at the cost of trillions of dollars, didn't come from nowhere.

The secret drive for China's 2060 target took shape inside Tsinghua University, where climate scientists had quietly spent more than a year modelling different pathways to reach net zero.

Professor Xie Zhenhua, a former environmental bureaucrat and veteran diplomat, oversaw the work from his threadbare office as head of the college's Institute of Climate Change and Sustainable Development.

Few within China's strict hierarchy can match Prof Xie's mastery of government bureaucracy and climate science, making him an influential voice on the issue among the ruling elite.

Prof Xie is modest about his role.

"We made policy proposals to relevant leaders and departments," he said in an interview on Tsinghua's campus in late October, dressed like a typical Communist Party cadre in a dark suit and pressed white shirt.

"It seems our proposals had some impact."

China and other developing nations had long held that wealthier countries who benefited from earlier industrialisation, heedless of the dangers from burning fossil fuel, should carry most of the economic burden for preventing catastrophic warming.

Prof Xie spent more than a decade as China's top climate diplomat, in the early years fiercely defending the principle that emerging economies have a right to uncontrolled carbon emissions.

On a population-adjusted basis, after all, far too much carbon dioxide began its journey into the atmosphere from smokestacks and tailpipes in the US and Europe.

At the 2011 international climate talks in Durban, Prof Xie gave a table-pounding speech calling out the hypocrisy of developed nations; news footage made him famous throughout China.

Now at the twilight of his career, he has done more than anyone else outside Prof Xi's ruling circle to position China as a global climate leader, establishing a carbon neutrality plan ahead of the US.

"When you first start, it's just a job," Prof Xie says.

"But after some time, when you see the impact you could bring to the country, the people, and the world, it is no longer just a job. It has become a cause, a higher calling."

At 71, Prof Xie should be happily retired after more than three decades shaping China's approach to the climate and environmental protection.

Communist Party custom requires members of Prof Xie's rank who turn 70 to relinquish official roles.

A rare exception allowed him to receive an appointment as special adviser to the Environment Ministry this year.

In that capacity, Prof Xie submitted the 2060 recommendations based on research his institute had done in coordination with a dozen government-linked think tanks.

The proposal likely arrived on Mr Xi's desk via Vice-Premier Han Zheng, who sits on the Politburo's Standing Committee and oversees the Environment Ministry.

Every major decision in China is made collectively by the seven men on the Standing Committee.

Ultimate credit invariably goes to Mr Xi, the nation's most powerful leader since Mr Mao Zedong.

Environmental protection has become one of Mr Xi's core issues as he has sought to temper the growth-at-all-costs mentality that dominated China's breakneck industrialisation.

Before the UN speech, though, Mr Xi had never spoken publicly about carbon neutrality.

The proposition was considered so remote that it was hardly mentioned by state media.

"China was reluctant to talk about concepts like net-zero emissions or carbon neutrality," said Mr Li Shuo, a prominent environmentalist in China who has spent years lobbying Prof Xie for more aggressive policies.

"Xie has played a part in bridging that gap."

To translate global climate imperatives into Chinese government policy, you need to be fluent in two extremely esoteric languages: sloganeering Communist Party-speak on the one hand, and the technocratic vocabulary of international climate negotiation on the other.

That's how Prof Xie manages the trick of advocating for the greater commitments other countries want from China without making them seem like concessions.

Examples of this unusual ability pop out of Prof Xie's interview: The 2060 goal, he says, will help China become a "great modern socialist power" and build "a community with a shared future for mankind", mottos Mr Xi has used to guide long-term policymaking.

Then, code-switching effortlessly, he explains that China's stance on "mitigation, adaptation, financing, and technology" will still need to be discussed at next year's COP26 UN Climate Change Conference, at which nations work out the details of the Paris Agreement.

Prof Xie's career has traced China's meteoric economic rise-and its reckoning with the damage left behind.

His tenure as the head of China's environment protection administration ended abruptly in 2005 after deadly explosions at a chemical plant in Jilin, a province near the border with North Korea and Russia.

The accident affected tens of millions of people.

Such an incident would have derailed the career of a typical civil servant, but Prof Xie bounced back and eventually ended up on the Communist Party Central Committee.

He took over the role as China's primary international climate negotiator in 2007, and his approach didn't always resort to denouncing developed nations.

A former colleague jokingly described him as "like a panda bear, very huggable".

"When you come to the negotiation table, you need to be honest and candid. People respect you for protecting your own country's interests," Prof Xie said, looking back.

"But you're also here to solve problems, to tackle climate change."

He clashed publicly with Mr Todd Stern, the US special climate envoy from 2009 to 2016, before hammering out a bilateral agreement in 2014 that brought China into the Paris Agreement two years later.

Leaked e-mails from the period show the two negotiators reminiscing like old friends, discussing future visits and grandchildren.

"He's somebody that I could always trust and somebody who I can do business with," Mr Stern says in a telephone interview from Washington.

"This is a very meaningful task," Prof Xie says.

"A climate negotiator has only rivalries and friends, but he has no enemies."

Days after Mr Xi addressed the UN, the Tsinghua scientists were ready to present their roadmap to 2060.

The plan called for a gradual energy transition over the next decade and a half, followed by a rapid acceleration requiring an almost seven-fold increase in solar energy and a near quintupling of nuclear power.

Some analysts worried about this two-speed approach. The incremental start defers the hardest decisions until 2035, for the next generation.

This gradual trajectory to net zero probably helped Prof Xie's plan face less pushback from top officials, according to two green activists who have worked with him. (They asked not to be named, as activists in China are often targeted by the government for criticising official policy.)

The activists said a more ambitious short-term move, such as accelerating China's 2030 target for reaching peak emissions, would have likely provoked a backlash.

China has also given itself a 10-year buffer, as most other major economies are working toward net-zero emissions by 2050.

This group includes the EU as well as Japan and South Korea, which swiftly followed Mr Xi's UN announcement with pledges of their own.

The US could be next, with President-elect Joe Biden calling for a 2050 target.

There's risk that the extra decade for China will increase the temptation by policymakers to postpone painful changes.

The grand vision for 2060 will have to be filtered through hundreds of official documents, beginning with the government's next five-year plan to be released in March.

Different ministries, local governments, and state-owned enterprises will then work the policies into their own blueprints, where things could get watered down or delayed.

Prof Xie believes the 2060 target will force short-term changes.

"The goal will be difficult or even impossible to reach if we rely on traditional technologies and maintain traditional ways of production, of living and consumption," he said.

"This sends out a clear signal: We have to transform fast and innovate big."

It's not climate scepticism that drives the resistance. Chinese schoolchildren are taught the science of global warming from a young age, and citizens are eager for the government to clean up the polluted air and water.

The main issue is the coal industry. China mines and burns half the world's supply, and the sector still supports tens of millions of jobs."

After Mr Xi endorsed the Paris Agreement, the Chinese coal industry launched a nationwide campaign to retrofit power plants with what it claims to be low-emission technology.

This effort was publicly endorsed by influential academics, and that support in turn gave the coal industry cover to build new plants.

On the very same day Mr Xi addressed the UN, a commentary in the People's Daily, a Communist Party mouthpiece, argued for the future of coal: "As long as coal is utilised in a clean and efficient way, it should be called clean energy."

Prof Xie thinks this time will be different.

"The ultra low-emission (coal) technology might have resolved the problems of air pollution and energy efficiency, but it can't solve the problem of CO2 emissions," he said.

"Now that President Xi has made public the goal, I believe people will start to see the investment risks there."

With the next round of global climate talks coming up in Glasgow and countries under pressure to boost their commitments, China stands to gain a lot of goodwill by coming out of the gate early with a bold declaration.

Turning the pledge into a domestic priority will be a challenge as the government faces pressure to keep its post-pandemic economic recovery going.

But it won't come down to choosing between climate action and growth.

China suffered record floods in 2020 that affected more than 70 million people and caused some 214 billion yuan (S$43.75 billion) in economic losses.

"The damage done by climate change is not in the future," Prof Xie says, "but right here, right now."