With many citizens growing concerned over the quality of the air in their communities and rising global temperatures, several intrepid cities have taken matters into their own hands.

The Sierra Club recently announced its list of 15 cities in the United States that have committed to 100 percent clean energy, as part of its Ready for 100 initiative, a campaign to get towns in America to pledge to be fully powered by renewable energy.

"Aspen, Burlington, and Greensburg have already achieved 100 percent clean energy," Orli Cotel, Deputy Communications Director of the Sierra Club, told weather.com. "The others all have pledges to do so and are working towards it now."

Jodie Van Horn, director of the Ready for 100 campaign, explained to weather.com that most of the cities have formalized their commitment through some sort of policy or mayoral proclamation. She said that the environmental group's goal for the year is to get one hundred cities to make the same commitment.

"This is a new milestone for climate leadership," Horn said. "This is the biggest economic opportunity of the moment, we know it saves people money, it creates jobs and we know that it makes our communities healthier and solves climate change."

"More people are seeing clean energy not as an obligation, but as a huge opportunity," she added.

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Aspen, Colorado

Aspen has long worked towards having its power grid fully supplied by green energy. David Hornbacher, the city's Utilities and Environmental Initiatives Director told the Aspen Times that the city signed a contract with wholesale electric energy provider Municipal Energy Agency of Nebraska to reach the clean energy goal.

"It was a very forward-thinking goal and truly remarkable achievement," Hornbacher told the newspaper. "This means we are powered by the forces of nature, predominantly water and wind with a touch of solar and landfill gas."

Burlington, Vermont

Burlington became the first American city to run on 100 percent clean energy in early 2015. The Vermont capital, which long boasted an environmentally-conscious reputation with many green city initiatives, made their renewable goal by purchasing a 7.4 MW hydroelectric facility on the Winooski River. It wasn't just for ecological reasons, the city said it was fiscally logical as well.

"The transition in thought from 2004 to 2008 was 'We want to do this' to 'This actually makes economic sense for us to do this,'" said Ken Nolan, the manager of power resources for Burlington Electric, in a report by the Associated Press.

Columbia, Maryland

In September 2015, Columbia announced it would offset 100 percent of its energy use from renewable sources and signed a 20-year power purchase agreement with SunEdison.

"With the completion of the Nixon Farm solar power plant, the people of Columbia now enjoy the environmental and cost benefits of getting 100 percent of their electricity from renewable sources," said Steve Raeder, SunEdison's general manager of Eastern U.S. commercial and industrial solar. "Solar energy is a clean, reliable source of energy that makes great financial sense for communities across the U.S."

East Hampton, New York

East Hampton's town board passed a unanimous resolution in May 2014 to have the city's electricity fully powered by renewable energy.

"Making the switch to clean energy is just the right thing to do, both for the environment and for keeping more money in the local economy and creating jobs here," East Hampton Town Supervisor Larry Cantwell told RELI.

Georgetown, Texas

Georgetown, Texas, which is situated in the middle of oil country, stunned many when it announced it would become the first city in Texas to be powered entirely by renewable energy. The city plans on building solar power plants which will provide Georgetown with 150 megawatts of solar power.

"I'm probably the furthest thing from an Al Gore clone you could find," Jim Briggs, interim city manager for Georgetown Texas told The Guardian. "We didn’t do this to save the world – we did this to get a competitive rate and reduce the risk for our consumers."

Grand Rapids, Michigan

Grand Rapids spearheaded a commitment to 100 percent green energy with the help of former Mayor George Heartwell. The clean energy goal was made by the Office of Energy and Sustainability and is also part of the city's comprehensive Sustainability Plan.

"I say to colleague mayors, 'Start something. Start small. Put solar panels on your city hall building. Stick some money away and do a geothermal project on one of your buildings. Or simply buy the RECs or buy the power from your public utility and get certification that it’s green power. But start some place.’ Once you get started, it actually feels pretty good," Heartwell told MidwestEnergyNews.

Greensburg, Kansas

Greensburg, Kansas was devastated by a massive tornado in May 2007. When the city rebuilt, local officials pledged to go green, with a thorough Sustainable Comprehensive Plan for 100 percent renewable energy. The City Council passed the plan in December 2007 and as part of that commitment, according to the Rocky Mountain Institute, the city "installed a 12.5 megawatt wind farm that supplies enough electricity to power every house, business, and municipal building in the town.”

Lancaster, California

In 2013, mayor of Lancaster, California, R. Rex Parris, wanted the city to become the "solar capital of the world." "We want to be the first city that produces more electricity from solar energy than we consume on a daily basis,” he told the New York Times. Parris led an initiative to place solar panels on many of the city's buildings including city hall, the performing arts center and the stadium. The Renewables 100 Policy Institute called it one of the "most expansive solar community programs ever undertaken."

Nassau, New York

In December 2015, Nassau, New York's town board voted to get 100 percent of its power from renewables by 2020. The small town, located outside of Albany, pledged to have "all six of the town buildings disconnected from the grid," according to Politico New York. "From a practical perspective, it’s possible,” Nassau supervisor Dave Fleming told Politico. "We have a lot of people resources in our community."

Palo Alto, California

In 2013, Palo Alto's city council voted in favor of committing to using 100 percent renewable electricity. "As a City, we've had cheaper, greener power for our citizens for decades, and being able to make this recent move to 100% carbon-free electricity is just another example of how owning our own utilities pays off," City Manager James Keene told RenewEconomy.

Rochester, Minnesota

In October 2015, Rochester Mayor Ardell Brede read a proclamation that the city would fight vigorously to meet a goal of 100 percent renewable energy by 2031. "At the heart of a successful 100% renewables strategy, it is fundamental to allow open participation in the development and financing of energy infrastructure," the proclamation said.

San Diego, California

In December 2015, after a unanimous City Council vote, San Diego announced it would become the "largest American municipality to transition to using 100 percent renewable energy."According to the New York Times, the city announced it planned to use solar, wind, and hydropower to achieve its renewable goals by 2035. "It’s not a partisan issue at all," Mayor Kevin L. Faulconer told the newspaper. "It's about putting a marker down. It’s the right thing to do."

San Francisco, California

San Francisco mayor Edwin Lee coordinated a Mayoral Task Force to advise the City on how to best achieve a 100 percent green energy goal, and was spearheaded by the San Francisco Environment Department as well as local energy leaders, and other government agencies. According to Go 100% Green Energy, this Task Force issued a recommendations report in 2012, which suggested "six strategies to get to 100 percent renewable power by 2020."

San Jose, California

San Jose's Mayor Chuck Reed first pledged in 2007 to have the city be run entirely on green energy by 2022. According to a report by SustainableBusiness.com, this will be achieved as part of a "10-point plan including a 50 percent reduction in energy use, the planting of 100,000 new trees, 100 percent recycling of wastewater and 100 percent renewable electric power by 2022."

Santa Monica, California

In January 2016, Santa Monica announced it would power its Municipal Operations with wind and solar. The beach city said it would get its green power from 3 Phases Renewables, a renewable energy power solutions provider.

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