At Pleasant Banyan Bay in China’s southern Guangdong province, couples flock by the dozens for elaborately staged wedding photos on the white sand. Large signs on a nearby hotel shout, “Forever.”

But the love on display here might outlast the sand. A rising sea has narrowed the main beach by 10 metres and scoured around trees, exposing their roots. Smaller beaches on the fringes of the bay have already vanished.

“I know the glaciers and the poles are melting and that’s why the water is rising,” said Chen Hong, 48, a lifeguard who has worked on this beach since 2000. Watching the water slowly creep upward has made him a pessimist.

“With the sea level rising so much, water is going to occupy a lot of land,” he said. “Earth may have given birth to humans. But it seems like, in the end, humans will destroy the Earth.”

No country on Earth has more people at risk from the sea-level rise than China, where 85 million people live on land that will either be flooded or at risk of inundation in the future, according to an analysis based on a six-metre sea-level rise published in Science this year.

A 900-page Chinese climate science report released recently points to sea levels as one of the chief risks to the country, saying some coastal “cities may even face risks of massive disasters that are hard to forecast.”

And Guangzhou, the capital of Guangdong province, will experience greater losses than any other major global city, the World Bank has warned. The sprawling industrial complex now rooted in the region’s Pearl River Delta has been a principal source of China’s enormous new wealth in recent decades. But what has proved fertile land for development has also come laden with the risk of floods. Most of the delta lies within a metre of sea level. About 13 per cent lies below sea level – not far off the 26 per cent in the Netherlands.

As sea levels rise, the World Bank forecast annual losses of $17.5-billion per year by 2050 for Guangzhou, the highest in dollar terms and, as a percentage of gross domestic product, among the world’s 136 largest coastal cities. Last year, the losses from ocean disasters in Guangdong totalled $1.25-billion, local leaders have said.

“Guangzhou is somewhere where there’s a huge amount of exposure, and I think it’s pretty vulnerable,” said Robert Nicholls, a professor of coastal engineering at the University of Southampton and one of authors of the World Bank report.

“Many of the cities in Asia are built on deltas, so they are by definition almost at the hazard water levels,” he said. “And climate change will make that worse.”

The toll of climate change looms large over China in the midst of the Paris climate talks, which the country entered with a posture far different from its past obstruction of global agreements. Chinese President Xi Jinping called Paris “a new starting point.”

In 2009, Beijing was singled out as the architect of failure at the Copenhagen climate talks. Delegates and secret recordings at the time described how China – which, in a snub, sent its deputy foreign minister to sit across the table from leaders such as U.S. President Barack Obama – sabotaged the talks, insisting that important targets be stripped out and, in the end, humiliating those who sought a landmark deal.

But the past 12 months have seen a sea change in China’s climate posture – an underappreciated pivot from laggard to leader.

Late last year, Beijing and Washington agreed to a surprise deal that would see China halt its emissions growth by 2030. It followed that up with a more detailed plan this June to cut emissions per unit of GDP by nearly two-thirds from 2005 levels. It then injected $4.1-billion into the South-South Co-operation Fund on Climate Change, money other developing nations can spend on projects to cope with global warming.

Beijing has been “engaging others very actively, to bring others together for a successful Paris process,” said Changhua Wu, greater China director for the Climate Group, a non-profit organization that advocates a low-carbon future.

It is driven, in part, by self-interest. The slowing of China’s economy has underscored the problems with the coal-heavy and carbon-intense development that has driven growth for nearly four decades. Chinese leadership now wants green energy to become a new economic pillar. It’s a strategy that aligns with national priorities on innovation, energy security and job creation.

And since China is already the largest manufacturer and consumer of wind and solar energy, the country has a running start.

“It’s a fascinating trend,” Ms. Wu said. Major countries “are literally transforming their economic structure and energy structure in order to address climate-change issues, and link that very, very closely with how they grow their economy,” she said.

Such a transition has had high-level champions in China, including Zhu Yanlai, the daughter of former Chinese premier Zhu Rongji.

She helped with a team that drafted a document on constructing “ecological civilization.” It outlines a multifaceted plan to direct infrastructure investment into greener technology; use credit and fiscal policy to push businesses into energy efficient systems; encourage education to emphasize green innovation; and employ propaganda to spread the word about conservation and reduced consumption.

Those ideas were earlier this year closely mirrored in a policy decision on “accelerating the development of ecological civilization” by the Central Committee of the Chinese Communist Party and the country’s State Council.

“Deng Xiaoping said to get rich is glorious. I think Xi Jinping will say ecological civilization is glorious,” said Laurence Brahm, founder of the Himalayan Consensus and one of the drivers behind the ecological civilization document.

Change has been driven not just by hope of a wealthier future, but also fear of a more challenging one.

“China is aware of how climate change is impacting various aspects of its society, from water, agriculture, urban centres, human health and so on,” said Rebecca Nadin, the Asia-Pacific regional director for green non-profit Intasave and co-editor of Climate Risk and Resilience in China.

Melting glaciers are raising fears about future water shortages. Rising temperatures have expanded the danger area for infectious diseases: Malaria risks are rising and last year, China saw 46,864 dengue cases, up tenfold from the prior year after an outbreak in Guangdong.

The breakneck pace of development has worsened local vulnerability, in particular to saltwater incursion that can damage crops and foul drinking water.

“The tendency of the salt tides is getting worse,” said Chen Tegu, a professor emeritus at the South China Sea Institute of Oceanology of the China Academy of Sciences in Guangzhou. He is the country’s first academic to study sea-level rise.

“The reason it’s getting worse is mostly because of human behaviour and activities,” he said, pointing to sand dug from river beds to fuel major land-reclamation projects, and reservoirs that have held back river water from the sea.

The region has been protected from the sea-level rise by well-built dikes, he said.

But dikes have their own risks: The higher they are built, the more catastrophic the consequences if they one day prove insufficient.

A recent Chinese publication, called The Third National Climate Change Assessment Report, warns that water levels are rising faster around China than the global average. “Climate change will make the urban conurbations along the coast the regions most affected by climate change nationwide,” it says.

The region’s vulnerabilities are already on display.

Just south of Guangzhou at Million Sunflower Garden, a tourist attraction with fields of bright yellow blooms, workers switch to tap water in the winter because encroaching salt tides turn the local streams saline. In those months, sunflowers are stunted and produce less than half their normal weight in seeds. “We have less output, the flowers are small and less colourful,” said Hu Xiangui, 28, who is in charge of the plantation. “It happens every year.”

Meanwhile, not far from Pleasant Banyan Bay, a crumbling stretch of shoreline near a highway toll booth stands as one of the area’s most striking symbols of what happens when the waves rise. Here, a section of land roughly eight metres wide and several hundred metres long has fallen down onto the shore below. The area once had a small beach. It is today mostly a jumble of rocks and concrete.

“It collapsed bit by bit,” says Zhao Shoujun, a cook at a nearby office.

A government sign now warns of hazards on a bicycle path that runs along the edge of the eroded land.

“They’ve suggested tourists not come here because it looks kind of dangerous,” Mr. Zhao says. “If there aren’t any dikes built, I think most of the coastline will become like this.”