Do You Live in One of the World's 15 Greenest Cities?

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These metropolises aren't literally the greenest places on earth -- they're not necessarily dense with foliage, for one, and some still have a long way to go down the path to sustainability. But all of the cities on this list deserve recognition for making impressive strides toward eco-friendliness, helping their many millions of residents live better, greener lives.

1. Rekyjavik, Iceland

Remember the grade-school memory device "Greenland is icy and Iceland is green"? It's truer than ever thanks to progress made by Iceland and its capital city in recent years. Reykjavik has been putting hydrogen buses on its streets, and, like the rest of the country, its heat and electricity come entirely from renewable geothermal and hydropower sources and it's determined to become fossil-fuel-free by 2050. The mayor has pledged to make Reykjavik the cleanest city in Europe. Take that, Greenland.

2. Portland, Oregon, U.S.

The City of Roses' approach to urban planning and outdoor spaces has often earned it a spot on lists of the greenest places to live. Portland is the first U.S. city to enact a comprehensive plan to reduce CO2 emissions and has aggressively pushed green building initiatives. It also runs a comprehensive system of light rail, buses, and bike lanes to help keep cars off the roads, and it boasts 92,000 acres of green space and more than 74 miles of hiking, running, and biking trails.

3. Curitiba, Brazil

With citizens riding a bus system hailed as one of the world's best and with municipal parks benefiting from the work of a flock of 30 lawn-trimming sheep, this midsized Brazilian city has become a model for other metropolises. About three-quarters of its residents rely on public transport, and the city boasts over 580 square feet of green space per inhabitant. As a result, according to one survey, 99 percent of Curitibans are happy with their hometown.

4. Malmö, Sweden

Known for its extensive parks and green space, Sweden's third-largest city is a model of sustainable urban development. With the goal of making Malmö an "ekostaden" (eco-city), several neighborhoods have already been transformed using innovative design and are planning to become more socially, environmentally, and economically responsive. Two words, Malmö: organic meatballs.

5. Vancouver, Canada

Its dramatic perch between mountains and sea makes Vancouver a natural draw for nature lovers, and its green accomplishments are nothing to scoff at either. Drawing 90 percent of its power from renewable sources, British Columbia's biggest city has been a leader in hydroelectric power and is now charting a course to use wind, solar, wave, and tidal energy to significantly reduce fossil-fuel use. The metro area boasts 200 parks and over 18 miles of waterfront, and has developed a way-forward-thinking 100-year plan for sustainability. Assuming civilization will last another 100 years? Priceless.

6. Copenhagen, Denmark

With a big offshore wind farm just beyond its coastline and more people on bikes than you can shake a stick at, Copenhagen is a green dream. The city christened a new metro system in 2000 to make public transit more efficient. And it recently won the European Environmental Management Award for cleaning up public waterways and implementing holistic long-term environmental planning. Plus, the pastries? Divine.

7. London, England

When Mayor Ken Livingstone unveiled London's Climate Change Action Plan in February, it was just the latest step in his mission to make his city the world's greenest. Under the plan, London will switch 25 percent of its power to locally generated, more-efficient sources, cut CO2 emissions by 60 percent within the next 20 years, and offer incentives to residents who improve the energy efficiency of their homes. The city has also set stiff taxes on personal transportation to limit congestion in the central city, hitting SUVs heavily and letting electric vehicles and hybrids off scot-free.