From the revitalization of city parks to urban bicycle-sharing programmes, urban sustainability interventions tend to be conceived, implemented and evaluated one municipality or neighbourhood at a time. Yet urban environmental processes occur on much larger scales. Projects that benefit one district may have negative impacts next door.
One example is environmental gentrification. As districts become greener, they become more desirable and expensive. The premiums placed on neighbourhood amenities such as walkability, public transport and the proximity of parks, farmers' markets and 'greenways' such as hiking trails and bike paths by residents who can afford to pursue them raise the cost of living.
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In Europe, the German city of Freiburg has been internationally recognized for its achievements in renewable energy, public transport, participatory planning and pedestrianized, energy-efficient districts. As the metropolitan region has become more desirable and expensive, more of its workforce has turned to the cheaper suburbs for housing. The city has grown more socially homogenous, while beyond its boundaries commuting has skyrocketed, as have the associated carbon emissions. Greening has come at the expense of community stability and racial and economic diversity, and has undermined regional environmental goals.