Reykjavik, Iceland

By most measures, Reykjavik tops the list of energy efficient cities worldwide. Along with the rest of Iceland, Reykjavik relies on renewable hydropower and geothermal plants to provide all of the heat, electricity and hot water for its more than 120,000 citizens. The Nesjavellir geothermal power station services all of the space heating and hot water needs of the greater Reykjavik area. The city plans on becoming fossil-fuel-free by 2050 and the final piece of that puzzle is hydrogen power. In the mid-2000s, the city began replacing its public transportation with hydrogen-fueled buses. The only “pollution” emitted from these vehicles is pure water. Although Iceland may be a small country, its big energy ambitions are leading the way for the rest of the world.

Vancouver, Canada

Vancouver gives Reykjavik a run for its money. In 2012, the city of Vancouver laid out an action plan to become the world’s greenest city by 2020. While that may seem like a big accomplishment in a fairly small amount of time, the city is well on its way. Hydroelectric power already accounts for 90 percent of the city’s energy supply, while the other 10 percent includes renewables like wind, solar and wave power. Add in Vancouver’s mass transit — nearly 250 miles of bike lanes and ride sharing programs — and the city has one of the lowest per capita carbon emissions of any major city in North America.

With a large off-shore wind farm and streets known for being incredibly bike friendly (with over a third of residents riding every day), the city of Copenhagen is considered by many to be one of the world leaders in clean technology. As part of the city’s goal to be the first carbon-neutral capital by 2025, green roofs have sprouted up all over Copenhagen, not only helping to insulate buildings, but also allowing water to be more slowly absorbed, lessening the pressure on sewers and drains. Plus, as the city’s website puts it: “Green looks good” and can provide a bit of nature in dense urban areas.

Oslo, Norway

80 percent of Oslo’s heating system is powered by renewable energy – mainly bio-methane from waste. In the next 10 years, the city hopes to get that number up to 100 percent. The city also uses “intelligent lights” that adjust their output depending on weather and traffic conditions, which have greatly improved the city’s energy efficiency. By 2030, Oslo hopes to reduce carbon emissions by 50 percent, while all of Norway hopes to be carbon neutral by 2050. Oslo also boasts “hugely successful” car and bike sharing programs. Thousands of electric vehicles are already enjoying “free parking, toll immunity, and access to lanes generally reserved for public transport.”

London, England

Beginning in the mid-2000s, London has committed itself to upping its energy efficiency. Its 2007 climate change action plan laid out plans to switch 25 percent of its power generation to more efficient, local sources, as well as cut CO2 emissions by 60 percent over the next two decades. The plan also offers residents incentives to improve the efficiency of their homes, while implementing stiff taxes on automobiles – hitting SUVs particularly hard (electric vehicles and hybrids are exempt). And it’s not just London that’s going green: England has 10 of the top 25 operational offshore wind farms.

Malmo, Sweden

Most of Sweden’s energy already comes from nuclear power and the country has reduced its consumption of fossil fuels by 25 percent from 2008 to 2012. Sweden’s third largest city, Malmo, has created an ambitious and innovative energy efficient housing plan. In a former shipyard called Western Harbour, the city of Malmo has constructed housing for 10,000 residents as well as space for 20,000 employees – all powered exclusively with “100 percent locally produced renewable energy from the wind, sun and water.” Along with measures for waste management, minimized transportation needs and increased biodiversity – this urban experiment could be the future of energy efficient living.

Boston, San Francisco, Portland and New York

These four U.S. cities topped the charts in the 2013 American Council for an Energy-Efficient Economy city scorecard.

The scorecard looks at key areas of efficiency, including transportation policies, local government operations, community-wide initiatives, utilities and building policies. Each city is scored out of a possible 100 points, with Boston coming out on top with 76.75 largely due to its community-wide programs and utility partnerships, including the Renew Boston Initiative.

San Francisco also often tops the list of greenest American cities. The city recycles 77 percent of its waste, reserves nearly 20 percent of its land for green space and has been a leader on the electric car front. In 2001, San Francisco residents approved a $100 million bond initiative to finance renewable sources of energy, including solar panels and wind turbines.

Portland has long been one of the most environmentally friendly cities in the U.S. With an eco-conscious citizenry that makes extensive use of bikes, the Pacific Northwest is green in more ways than one. Portland has replaced its traditional street lights with LEDs and has the goal of someday relying 100 percent on renewable energy sources.

The gritty streets of New York may seem like a surprising place to find renewable energy, but the Big Apple tied for third in the 2013 scorecard. New York was a leader in community-wide initiatives, building policies, utilities and public benefit programs as well as access to energy data. New York has long been known for its subway and transit systems and the city plans to double its recycling rate to 30 percent by 2017.