Only a fast and global transformation towards decarbonization and sustainability can keep the Earth in a civilization-friendly state. Cities play an important role in this transformation: they are responsible for a dis-proportionally large part of greenhouse gas emissions, and simultaneously are one of the main drivers of sustainable policy innovation and adoption. Learning from each other to reduce, prepare for and react to the coming environmental changes, they can be conceptualized as nodes in a globe-spanning network. This network model may be approximated by the global air traffic network, political and trade relations, and other city-to-city connections. Such a learning network model may also yield insights into the social tipping dynamics that are so urgently needed to control the human impacts on the Earth System [1].
The aim of this study is identifying whether network-based transmission effects are dominant in sustainability policy adoption by by cities, and which networks have the highest prediction power for this spreading process. For this purpose, we analyze the spreading of several municipal policies and innovations related to sustainability transformations as contagion processes on such inter-city networks. We extract several networks, comprising different types of city interconnections, from empirical data. Examples investigated as spreading innovations are the implementation of Bus Rapid Transit public transport systems (see Figure 1), and membership in a sustainability organization. The spread of these urban technology and policy innovations are then investigated using a dose-response-contagion approach [2], combined with surrogate data methods [3].
[1] I. M. Otto, J.F. Donges et al., PNAS, vol. 117 (2020) 2354
[2] P. S. Dodds and D. J. Watts, Physical Review Letters, 92 (2004) 21.
[3] J. Theiler, S. Eubank, A. Longtin, B. Galdrikian, and J. Doyne Farmer, Physica D: Nonlinear Phenomena, 58 (1992) 77