Yet another big Chinese city is sprouting up in no man's land like a magic beanstalk.

Dongtan, near Shanghai, will occupy Chongming Island, roughly equal in size to Manhattan. By 2010, its first condos and commercial space will be on the market. A 12-mile bridge and tunnel will get residents to Shanghai airport and the financial district, in under an hour. By 2050, half a million residents will call Dongtan home.

But this is not just another Chinese exercise in conjuring cities out of dust and migrant worker sweat. Dongtan will test the theory that a city can get greener as it grows. Sustainability is not just an au courant feature of this community-in-the-works, it is the central focus.

Arup, the global consultancy behind Dongtan, is forsaking form with a few green functions. Instead, every element of the city's design will be integrated to promote sustainability and conservation. The super-efficient buildings, powered by local renewable energy, will be grouped in clusters that defy urban sprawl and obviate the SUV. A good thing, too, as any CO2-spewing vehicle will be banned from Dongtan. A matrix of organic farms will be a close food source, and 90% of all waste will be repurposed.

Although well-underway now, the scale of the Dongtan must have overwhelmed Arup architects and engineers visiting Chongming Island for the first time, back in 2004. Chongming gathers silt from the Yangtze as the river pushes into the China Sea, essentially a 1200 sq km sandbar. Even today, visitors to its modest little port see far less construction than wetlands and rice paddies. In fact, it seems suspiciously underdeveloped for land so close to metropolitan Shanghai. But the Dongtan project is owned by Shanghai Industrial Investment Corporation, operated by the municipal government, and acquired a good part of the island during the Asian financial crisis. Rather than look for a developer who could most comfortably line pockets and municipal coffers, the Shanghai government insisted Chongming Island stay as pristine as possible. The mandate led to a bunch of conjecture - bedroom communities or retreats for Shanghai's elite - but no solid vision.

Enter Arup, who had first visited the island to advise McKinsey on how to preserve the rare spoonbill's wetland habitat, but now had other ideas. Arup is way beyond an architectural firm, offering economists, energy experts, even anthropologists to advise on global projects. The firm had a new department it called "integrated urbanism", which hoped to pioneer the emerging field of redesigning entire cities for sustainability. Chongming was an ideal opportunity, and SIIC was prepared to listen.

Arup's vision was a far cry from the lawns and condos model so dear to suburbia, and so reliant on automobiles. Nor would the sardine standards of Hong Kong do. It discovered that fifty people per acre, roughly the population density of Stockholm, is ideal for energy consumption, encouraging biking and walking. These metrics would make bungalows and split levels impossible, but skyscrapers certainly weren't an option either. Arup estimated that with all buildings between four and eight stories high, Dongtan could sustainably support a population of half a million, leaving more than three-fifths of the land available for parks and farms, as well as the spoonbill's wetland habitat.

Those wetlands posed a challenge to earlier planners, who out of respect for flooding proposed a city stuck to the middle of the island, no advantage taken of the waterfront. But after touring Suzhou and other Chinese water towns, Arup planners realized that they had an ancient blueprint for harmoniously incorporating canals and ponds into Dongtan's design. The finished city will have flood cells to trap sea water and hills serving as natural storm barriers, along with a sophisticated drainage system.

The power plan credits the resourceful genius of the minds at Arup. Instead of growing the biomass to burn for turbines and electricity, Dongtan will use the mountains of rice husks left behind in China's staple agricultural industry. Putting the plant downtown will allow it to heat and cool every building on the island. Add to that a wind farm, solar panels, and plentiful small wind turbines, and Dongtan just might hit the lofty goal of 100 percent of its energy derived from renewables, when it opens in 2010.

Conservation initiatives will help in the quest. Underground farms will stack organic crops, all grown under solar-powered LEDs. Twin water networks will deliver drinking water to kitchens but treated waste water to toilets. Zero-emission delivery trucks will haul shared loads from the rigs parked at the edge of Dongtan. Even the heretofore inviolable fen shui rule of north-south city grids will be bent, along with Dongtan's axis, to allow for tree positioning that maximizes summer breezed and blocks winter gales.

Urbanization is the 21^st century's megatrend. By 2050, two-thirds of the world's population will live in metropoles like Shanghai. While it's probably too late for New York, London and Los Angeles to adopt revolutionary approaches to their eco-challenges, Dongtan will hopefully serve as a model for developing urban centers, proving that economic and social progress don't have to come at the price of environmental degradation.