Welcome to Emerald City, sustainable eco-lopolis of the future!

Earth’s perfect green city already exists—in pieces. We’ve gathered the world’s most innovative buildings, utilities and initiatives into our eco-topia. It’s an eco-fantasy now, but not for eco-long!

CNN.com

Seventy percent of the world's population will live in cities by 2050. And creating a sustainable urban environment will be vital to reduce skyrocketing demands for energy, both to curtail toxic emissions and to ensure power for future generations.

We looked for the best of what's already out there, tapping U.S.-based sustainability think tank the Rocky Mountain Institute for its expert opinion. According to the RMI, while components like wind turbines, energy monitoring systems, solar panels, public transportation and others can individually contribute to a city's eco-friendliness, the way to make a truly green city is to integrate them all.

Of course, the ideal city is no city at all. The next best thing is a community that draws its fuel from waste in a "closed loop" and emits no carbon. And even better than a carbon-neutral city is a regenerative city -- one that reuses its waste, replenishes its diminishing soil through compost and generates renewable power.

Below isn't a complete list of everything out there, but rather a diverse set of innovations that demonstrates the range of sustainable technologies and their applications.

1. Geo-customization

The future of building in Emerald City is in conforming to our surroundings. Or the present, if you’re in Guangzhou, China, where in 2010 the Pearl River Tower -- a 71-story alter to form, function and green architecture -- will self-generate enough power to meet its energy demands using wind turbines, photovoltaics, automated blinds and rainwater retention in concert with an anatomy that’s tailored to harness the sun and wind patterns unique to its surrounding landscape. Like a lot of features in Emerald City, these examples won't be limited to commercial enterprises but be part of the design of all structures including residential areas. Check out the UK's BEDzed project.

2. Recycled water

The most critical resource in Emerald City -- besides its honest, hardworking people, of course (CNNGo for mayor 2028!) -- is water. Demand is growing while supply is dwindling, so nearly every drop that’s used is reused through advanced wastewater reclamation. Known today in Singapore as NEWater, it’s currently serving industries and citizens there, where roughly half of all water must be imported from Malaysia.

3. Industrial ecology

In Emerald City, industry will demand interdependency. Here, otherwise toxic by-products from one facility will act as raw material for the others surrounding it, creating a sustainable loop of industrial outputs. Right now in Copenhagen, Denmark, wastewater from a refinery serves as coolant for an adjoining power station, which yields particulates used to produce building materials at a neighboring wallboard manufacturer.

4. Passenger-powered subway

Every thing in motion, right down to the clopping of commuters' feet has the potential to produce energy. In Emerald City, the very footsteps of subway riders can be channeled to help power the train system’s operations. Sound ridiculous? Sounds Japanese to us! Tokyo Station right now features a piezoelectric floor that turns foot traffic into 1,400 kilowatts a day, powering ticket gates and display systems.

5. Passive buildings

Construction in Emerald City will incorporate “passive design,” such as natural ventilation, insulation and sunlight as a power source, cutting a building's energy demand. “Cities are often seduced by more expensive renewable technologies (supply) instead of reducing the demand first," says Rocky Mountain Institute's Coreina Chan. One example is the National Energy Lab of Hawaii, whose sustainable design features enable it to produce more energy than it consumes -- making it a net-zero-energy building.

6. Electric vehicles

Until science nerds devise practical hydrogen fuel cells, electric vehicles (EVs) are still Emerald City’s cleanest people-moving alternative. Hong Kong is putting us a step closer to resistor-based reality with the homegrown MyCar, a nifty EV that reaches 64km/h and can travel 112km on a full, six-to-eight-hour charge. Weighing a mere 726kg, the MyCar embraces a toy car image with a range of eye-popping candy colors.

7. Urban farming

Arable farmland isn’t exactly synonymous with dense commercial real estate, so to resolve agriculture with popular culture, Emerald City will have to be creative. Enter: the rooftop farm. Venture-capitalist-turned-urban-farmer Kazuki Iimura has been putting Tokyoites back in touch with their agrarian roots, having converted an unused plot of land near Chuo Dori into a rice paddy in Ginza and rooftops in Omotesando into vegetable gardens. Enter also: Havana, Cuba. Here, around 50 percent of the vegetables chopped, diced and eaten in the city are within its urban areas and grown in backyards, rooftops and container beds, mini-garden plots, workplace gardens for employees, and larger gardens. (YouTube video)

8. Hydro-neutral buildings

While the focus may be on energy, water is a vital part of Emerald City's sustainability and its buildings will have to recycle their share of it. One example out there: Deutsche Bank's Frankfurt headquarters, where renovations toward carbon neutrality are currently underway. Among its initiatives, rainwater and greywater (waste from things like washing dishes) is collected, treated and reused in toilets and irrigation systems. Combined with heating the bulk of its hot water via a solar thermal system, this water concept slashes water usage by 74 percent.

9. Free wheels

Our cities are only getting more bloated … along with their residents. So, free bike rentals won¹t just minimize traffic congestion and ease emission levels in Emerald City, they’ll keep its residents hot-bodied and healthy too. In Bangkok, the city has committed 10 million baht (approx. U.S.$300,000) toward making free bicycles available at kiosks all over town in exchange for a passport or ID card.

10. Retrofitting

Rather than relying solely on the construction of new high-tech buildings, Emerald City will also retrofit old ones, in possibly the most effective way to curb overall carbon emissions. In New York, the iconic Empire State Building is undergoing a $13.2 million project to reduce its energy consumption 35 to 40 percent, yielding $3.8 million in annual savings. That means the costs of retrofitting will actually make money for the ESB in just a few years.

11. Recycled food

Wet trash from Emerald City’s sundry dining establishments could feed a biomass-recycling complex no larger than a loft apartment. They’re doing it in Mumbai, where a dockside kitchen garden processes enough fertile food waste to grow produce for over 30,000 people in 1,000 square meters of space. Over 120 varieties of trees, shrubs and herbs grow here, become grist for the adjoining kitchen, and are tossed again as waste, starting the cycle anew.

12. Frankenstructures

Everything old about Em City construction has a chance to be new again with building materials for modern projects mined from the ruins of demolished ones. The 26-room eco-chic URBN hotel in Shanghai was adapted from an old factory, using locally sourced recycled materials (wood and reclaimed brick from old houses and other structures) for the rest.

13. Urban forest

Plants are good. They take nasty, earth-warming CO2 and, through the magic of photosynthesis, turn it into breathable oxygen. Like money, you can never have enough of ‘em, especially in Emerald City. That's why Singapore launched Gardens by the Bay, a continuous ring of greenery that will stretch over 54 hectares (approximately 72 soccer fields) around the Marina Bay area, marked by enormous “super trees” that will provide the gardens with shade, shelter and a steady source of rainwater.

14. Solar greenlots

Em City’s massive fleet of electric taxis, delivery trucks and passenger vehicles will need power, and that power’s gotta be cheap, abundant and, preferably, self-sustaining. In Singapore, solar charging stations are currently on trial at the Singapore Polytechnic campus, generating clean electricity from the sun. They're self-sufficient, clean and, in sunny Singapore, a potential game-changer.

15. Art is trash

Emerald City’s artists won't use new materials, they’ll create beautiful works from the city's waste. That’s been the preferred media since 2001 for monks at a Bangkok temple, where sculptures are molded from discarded steel rods stuffed with used cloth and covered with a mixture of cement, sand, water and used paper. Instead of fountains, realistic-looking waterfalls covered in live plants made with plastic bottles help treat sewage by increasing the amount of oxygen dissolved in the water. Another example of recycling and reusing that make Emeraldites a deep shade of green.

16. Green golf greens

Hundreds of acres of manicured countryside requiring untold amounts of water, pesticide, and fertilizer – yeah, golf’s a big red mark on the planet’s health chart. But Emerald City duffers won’t have to give up the sport they love (bollixing). It’s happening at Hong Kong’s Kau Sai Chau golf course, where its 200-strong fleet of solar-powered golf carts -- as well as the ferries that serve its members – will yield US$6 million in solar savings over 15 years. The course is also a Certified Audubon Co-operative Sanctuary for Wildlife.

17. Twist of freight

Cargo enters most cities at a huge environmental cost: at least 10 percent of greenhouse-gas emissions are linked to shipping. But Emerald City relies on locally sourced goods, reducing the need for freighting in the first place. Where it’s required, trucking fleets will be more efficient, getting greater mileage. Shipping is also more efficient -- containers are lighter weight, goods are added to reduce transportation of half-full containers and fewer empty containers are moved. Better tracking, security measures and load optimization will also bolster efficiency.

18. Harmonious habitats

Emeraldites seeking a weekend of carbon neutrality will take refuge in a place like the Machan tree house, found in the tropical forests outside Mumbai. This environmentally integrated guesthouse is completely off the grid -- even through its machine-free construction -- generating its own power via wind turbines and photovoltaic cells. No trees were harmed during the making of this hotel.

19. Eco-court

You won’t want be caught dumping chemicals in Emerald City, where justice toward polluters will be swift, righteous and without mercy! A separate trial system will tackle such cases specifically, presided by judges versed in the nuance and science of environmental policy. It’s the kind of earth justice now being meted in the Philippines, where 117 courts and their personnel have been specially appointed to address the increase in industrialization of the region and its subsequent environmental legalities.

20. Wind and sun -- like printing money

Emerald City will use no fossil fuel and will generates enough renewable power to charge its transport fleet, among other things. The result: a surplus of energy that can be sold to a power utility and returned to the grid, then sent somewhere less sustainable. That utility, rather than relying on coal or nuclear power, will use renewable energy sources like wind and solar power to provide electricity. Since the wind doesn't blow, nor the sun shine, all of the time, these systems will be interconnected with the utility to make sure it draws from each when appropriate.

21. Recyclable buildings

True infrastructural nirvana in Emerald City means that the buildings housing our beds, retail goods and special events will be as recyclable as the bottles housing our soda. In preparation for the Shanghai 2010 Expo, organizers have constructed a pavilion consisting of thousands of tubes made from recycled CD cases. More than simply using recycled materials, the long-term plan is to recycle the tubes again when the building is torn down.

22. Mass in gear

Emerald City will boast the inter-connected public transport system we all dream about. A mass network of trains, light rail and electric buses will reduce the need for individual transport, as well as the city's overall carbon footprint. When individual transport is necessary, bikes and small electric vehicles will serve efficiently. Many cities are incorporating biking into their transport plans, with Tokyo trialing electric taxis, Toronto aiming to build an elevated bike-way and Denver using a hybrid shuttle bus.

23. Smart grid

Something’s going to have to deliver power to all of this space-age technology, and it won’t be the infrastructural jalopies that major cities have been running on for the last 100-plus years. Emerald City’s power chassis will be a smart grid that communicates with the equipment it powers, activating and deactivating appliances depending on demand or cost at a given time of day. Customers in Boulder, Colorado, are test subjects on just such a grid, where sensors alert utility managers to problems, and renewable sources can be plug-and-play integrated.