Clean energy, public transit and local food make these 10 big cities the greenest of them all.

Honking cars emit foul black clouds, skyscrapers blot out the sun, litter lines the gutters and healthy green space can be hard to come by. But in many of America’s biggest cities, these negative traits are being eclipsed by clean, efficient public transit, bike-friendly infrastructure, multiplying trees, reliance on renewable energy and a fierce pride in locally-produced products. Slashing greenhouse gas emissions and coming close to zero waste is no easy feat for a metropolis with a population of at least 250,000, but these 10 cities – from Boston to San Francisco – prove that sustainability is possible on the largest of scales, in good economic times and bad.

10. Boston, Massachusetts

Representing the entire East Coast in impressive renewable energy stats, Boston boosted its solar power with the Solar Boston program and counts wind among its top three sources of electricity, with a turbine on city hall and more slated for several public schools. Other big plans include turning fall leaves and other yard clippings into power and fertilizer with a new biogas facility, and using recycled trash to power homes. For those residents who don’t rely exclusively on the nation’s most utilized public transportation systems, taxis will soon be another green option as they’re all required to go hybrid by 2015. New bike lanes and 250 bike racks have increased Boston’s pedal power, and the city saves a whopping $400,000 a year thanks to LED traffic lights.

9. Denver, Colorado

The Mile-High City is an outdoor wonderland with 14,000 acres of parkland in the mountains, 200 parks within the city limits, 850 miles of dedicated bike trails and 29 recreation centers. Denver preserves and protects its active, natural heritage with conservation measures like a no-pesticide policy in its parks and the Mile-High Million program, which plans to plant one million trees in the metropolitan area by 2025. For a city in a semi-arid region, Denver is adept at managing its water consumption, offering residents incentives to keep their usage down. Any concrete going into new city projects must be green, and Denver has also made some significant renewable energy goals, hoping to run on 20 percent wind power by 2020.

8. San Jose, California

Maybe it’s not California’s best-known or most-beloved city, but San Jose deserves some serious accolades for its clean-tech goals and innovations. Angling for the title of clean tech capital of America, San Jose has already created over 25,000 jobs in green industries and actively works to lure green businesses to the city. In fact, after Tesla Motors relocated its headquarters there in 2009, San Jose began rapidly developing infrastructure for electric vehicles including plug-in charging stations. It’s home to many of the nation’s top solar manufacturers as well as the world’s largest testing facility for solar products.

In a bid to become a zero-waste city, San Jose has managed to divert 62 percent of its waste to recycling and plans to reuse 100 percent of its waste water for landscaping within the next 15 years. The city’s Green Vision plan also includes a goal to reduce per capita energy use by 50 percent and get 100 percent of its energy from renewable sources within the same time period.

7. Oakland, California

Hop on a zero-emissions bus for a tour of one of America’s model green cities, checking out dozens of urban farms, renewable energy projects and a wide variety of eco-friendly businesses. Oakland is working to rise above high levels of unemployment and poverty to position itself as a leader in sustainability, particularly in the areas of local food, green jobs and renewable energy. Taking cues from its bigger Bay Area sister San Francisco (and sometimes even eclipsing it), Oakland gets 17% of its energy from renewable sources like hydroelectric, biomass and wind, and in 2007, it won the City Solar Award from NorCal Solar for having more solar power wattage than any other big city in Northern California.

The city aims to lower its greenhouse gas emissions to 36 percent below 2005 levels by the year 2020, the most ambitious target in the nation. It’s also home to Van Jones’ Ella Baker Center, one of several local organizations that focuses on training low-income adults for jobs in green industries.

6. Austin, Texas

Austin may be best known for its vibrant music scene, but this city shines just as bright in the sustainability arena. Not only is Texas’ capital city bicycle and pedestrian friendly, with plenty of mass transit and even hybrid plug-in stations, but its building codes encourage green practices and home energy audits are mandatory when selling a house. Austin is also the largest local government to run on 100% renewable energy, and by 2020 the city aims to have 30% of its residential, commercial and industrial energy consumption shifted to clean sources.

Birthplace of Whole Foods, Austin is brimming with organic restaurants and natural food stores, including America’s first zero-waste, packaging-free grocery store, In.gredients. If you’ve never been there and imagine the entire state of Texas as a dusty wasteland full of tumbleweeds, banish that notion from your mind, at least as it pertains to Austin – this city is surprisingly lush, offering stunning outdoor settings for biking, kayaking, swimming or just relaxing.

5. New York, New York

The fact that the Big Apple can compete with much smaller cities like Austin and Oakland is reason enough to land it in the top five greenest cities. It’s undoubtedly no easy task to keep a teeming metropolis of over 8 million residents from turning into an environmental nightmare, and while New York City can’t boast quite the same statistics on clean air or water conservation, it excels in public transportation and does surprisingly well on greenhouse gases and public park space. It’s the city’s very density that makes it so efficient, with just 20 percent of the population driving their own vehicles on a regular basis. Tall, jam-packed skyscrapers are more energy efficient than single-family homes, and of course, they use up a lot less land. Mayor Michael Bloomberg is further kicking up the city’s eco credentials with tree-planting programs, hybrid taxis and a program that phases out heavy heating oils.

4. Chicago, Illinois

Boardwalks, parks, nature centers, organic restaurants, green hotels and lots of eco-friendly shops: Chicago definitely has a lot to boast about. The United Nations chose it as one of just two U.S. cities for UN-Habitat’s 100 Cities Initiative for its work over the past two decades addressing climate change and healthier, greener living in general. Since 1989 the city has seen 500,000 trees planted, 10,000 bike racks installed, 114 miles of bike lanes established and 900 acres of abandoned, polluted land returned to productive use.

Chicago’s City Hall boasts a stunning rooftop garden, adding to more than 2.5 million square feet of green roofs within the city limits – more than all other U.S. cities combined. A downtown airport was demolished to make way for a 100-acre park, adding to the city’s reputation as a testing ground for reducing the urban heat island effect. The city is also making headway on a 2008 climate goal that aims to reduce greenhouse gas emissions by 80 percent come 2050.

3. Seattle, Washington

All of those waterways surrounding Seattle don’t just give it its postcard-perfect beauty and contribute to its wet, mild climate – they also provide over 90 percent of the city’s power in the form of hydroelectricity, and more low-impact hydropower plants are planned to reduce impact on wildlife like salmon. The city’s two global warming initiatives, Seattle Climate Action Now and Seattle Climate Partnership, have distributed thousands of home energy efficiency kits to residents and urged over 100 local businesses to reduce their greenhouse gas emissions. And when something like blackberry brambles threaten to overtake Seattle City Light’s substations, the utility employs a chemical-free solution: goats.

2. Portland, Oregon

Seattle’s carbon-neutral electricity makes it the star of the Pacific Northwest when it comes to climate change, but Portland has it beat in all-around sustainability and green living. A quarter of Portland’s workforce commutes by bike, carpool or public transportation with about 9,000 city residents biking downtown every day. The first city to adopt a climate change action plan, Portland offers free plug-in parking spots for electric vehicles and has more LEED-certified residential towers than any other city in the U.S. Portland is beating back sprawl with zoning regulations that encourage dense urban growth while leaving farmland for agricultural use. And on top of all of this, Portland has rightfully earned a reputation as a laid-back, eco-friendly place to live thanks in part to a lively local food and beer scene.

1. San Francisco, California

While Portland and Seattle are snapping at its heels, San Francisco manages to hang on to its title as the greenest city in America for a number of reasons, not the least of which is that city residents seem to have concern for the environment encoded into their DNA. Voters routinely approve aggressive green programs like banning plastic grocery bags and financing renewable energy for public facilities. San Francisco diverts a jaw-dropping 70 percent of its waste thanks to mandatory recycling and composting, and urban farms produce 20 times more food than the city’s residents can consume in a year. Nearly half of all San Francisco residents bike, walk or take public transit every day. Despite being more populated, San Francisco has a lower annual output of greenhouse gases than its Pacific Northwest competition, and is on track to reach its goal of 20 percent below 1990 levels by 2012.

Images: Tony the Misfit, Manu_H, dherrera_96, Wikimedia Commons, Ella Baker Center, Andreanna Moya, njt4148, compujeramey, wordridden, periwinklekog, kevincole