Leaders among environmentally conscious municipalities address these issues by retrofitting and constructing buildings to be energy-efficient; by expanding public transportation and introducing nonpolluting trains and buses to curb greenhouse-gas emissions; by offering tax incentives for businesses or residents to switch to renewable energy; by preserving farmlands and green spaces; and by recycling trash.

Some policy and technology experiments fail, said Suzanne Malec-McKenna, Chicago environmental commissioner in 2007–2011. But those that prove feasible often get implemented on a larger scale, improving the environment in an entire state or region, she said.

(AP Photo/Stephen J. Carrera)

Local governments are well-suited to fix environmental problems; they make their own, distinctive policies and control budgets. They also are smaller, less bureaucratic and closer to constituencies than national or international institutions, say Tommy Linstroth and Ryan Bell in their book Local Action: The New Paradigm in Climate Change Policy. The greater efficiency of city governments allows cities the flexibility to adjust policies mid-course if necessary.

Approaches to sustainable environmental practices differ, but leadership by mayors and dedicated resources (i.e., budgets) are common characteristics of the municipalities making the greatest strides, according to Linstroth. Engaging businesses and residents also matters, he said.

Municipal leaders use regulations, incentives, investments and public outreach to implement their environmental agendas. Wade Crowfoot, who has worked on the San Francisco mayor’s and California governor’s environmental initiatives, said city and state leaders have been willing to try novel approaches.

During recent years, Chicago city officials and residents planted half a million trees.

In 2001, the city pioneered a rooftop garden atop the 11-story City Hall. Today, Chicago boasts 418,000 square meters of high-rise greenery. Rooftop gardens save energy, help control rainwater and ease unnatural temperature spikes in compact urban centers. More than 120 environmentally sustainable buildings, many with green roofs, make Chicago a national leader in green building.

Portland, Oregon, boasts the highest percentage of bicycle commuters of any large U.S. city.

City residents enjoy not only one of the most extensive networks of bikeways in the country — more than 500 kilometers — but also can count on a city bicycle coordinator, free cycling maps, ample parking, and even a bike-through window at a fast-food restaurant. Some employers offer workers incentives to bike to work. The conveniences and incentives have produced an almost fivefold increase in the number of bicyclists in Portland since 1990.

The Pittsburgh-based PNC Financial Services Group is building what it hopes will be the greenest skyscraper in the world.

From a declining industrial metropolis with steel mills spewing black smoke and soot into the sky, Pittsburgh has transformed itself into a vibrant green city. Thanks to collaboration among city leaders, labor, business, academia and nonprofit groups, clean-energy projects and startups drive a new economy, creating well-paid green-collar jobs.

Los Angeles, operating 2,000 buses during peak hours, boasts one of the greenest bus fleets in the world.

The city suffers fewer days of smog, or “red alert,” than it used to. Its ozone pollution and harmful-particle indicators have declined over the past few decades.

As a result of federal and state automobile emission standards, cars and buses emit fewer pollutants into the air. Local regulations, forcing higher energy efficiency and environmental features in commercial buildings, also reduce air pollution.

Still, city leaders know they must do more to improve air quality.

New York has the largest share of residents who “think and act eco-consciously” among major cities.

The five boroughs that make up the Big Apple are home to one of the most environmentally friendly transportation systems and land-use regimes in North America. More than half of the city’s bus fleet runs on alternative fuel. Through redevelopment of post-industrial sites and vacant lots, New York has also expanded its green spaces. It has improved its air quality by replacing heavily polluting heating oils with cleaner fuels. Its carbon dioxide emissions per capita are lower than those in other U.S. cities.