The Greenest Cities

Though two American cities made the list, it is mostly the European cities that are leading the world in urban sustainability, reports Matthew Knight of CNN.

In compiling the list of the world's most green cities, a number of environmental measures were taken into consideration, such as availability and popularity of mass transit, renewable energy, scenery, green space, and water management.

Those models that "blaze a green trail," according to the article, include: Curitiba, Portland, Reykjavik, Chicago, Copenhagen, Frieburg, Malmo, Masdar, and Vancouver.