It also recognises that environmental policies that do not support economic growth and wealth creation are not sustainable in the long term. The OECD Green Growth Strategy (2011) defines the concept as follows: “Green growth means fostering economic growth and development while ensuring that natural assets continue to provide the resources and ecosystem services on which our well-being relies. To do this it must catalyse investment, competition and innovation which will underpin sustained growth and give rise to new economic opportunities." A need for new sources of urban growth: given the negative externalities generated by urban agglomeration and cities' urgent need to reduce their energy consumption and greenhouse gas emissions, urban areas have the opportunity to conduct environmental policies that can foster these new sources of economic growth.