The following are currently considered to be the top five most sustainable cities in the world:  VANCOUVER, CANADA; SAN FRANCISCO, U.S.; OSLO, NORWAY; CURITIBA, BRAZIL; and COPENHAGEN, DENMARK.

When it comes to implementing sustainable initiatives these cities are leading the globe in how that achieved and/or can achieve sustainable cities through using renewable energy and by cutting back on emissions. Among common sustainability characteristics of these cities (http://archive.rec.org/REC/Programs/SustainableCities/Characteristics.html) are:

leadership in using and developing renewables; green transport and traffic with low emissions; strict and green buildings with improved energy efficiency and ongoing LEED-certified green building projects); high marks for air quality and clean environment; waste management with efficient and high recycling rates; reserve high percent of land to green spaces, ongoing projects for efficient electric car traffic (Vancouver and San Francisco); protected forest, parks waterways, and agriculture land (e.g. Oslo, Curitiba); intelligent lighting adjusting intensity depending on traffic conditions and weather (Oslo); bio-methane from waste to power mass transit and heating; projects for cutting carbon emissions by 50 percent in coming decades with goals to be the world’s first carbon neutral capital by 2025 (Copenhagen); heating system powered by high percent renewable energy, mainly from biomass from residual waste with plans to reach 100 percent renewable sources for heating in most the cold regions in the world (Oslo); innovative program that allows people to exchange trash for transit tokens or fresh produce (Curitiba); projects to get 50 percent of the population on two wheels by 2015 by closing down some major roads to cars and developing an additional 43 miles of bike lanes and requiring all new developments to incorporate some level of vegetation into building designs (Copenhagen).

http://www.ecomagination.com/top-five-most-sustainable-cities-in-the-world