How hard is it for urban economies to become ‘green’?

Home to over half the world's population, cities are the drivers of the global economy and the primary influencers of the Earth's sustainability. Thus, the burden of sustainable economic development falls ever more on cities, with many global organizations and governments calling for the promotion of ‘green’ economies. Yet how does a city move from its current economic structure to a green economy? Using detailed occupational data for US cities, we develop a green jobs index based on the network of interdependencies between occupational specializations. Using this index we quantify how close a city's current economy is to the green economy. We further show that movement or transition through this ‘occupation space’ toward a green economy is a slow and difficult process, with the average annual movement towards a green economy across all US cities being close to zero. Such difficulty is uncorrelated with a city's current population size, density, per capita GDP, per capita income, or even the city's current green jobs index. Furthermore, the structure of occupational interdependencies gives rise to suboptimal movements towards the green economy.