Beyond borders: Assessing global sustainability through interconnected systems

The many complex interconnections among countries driven by natural and socio-economic processes have a crucial impact on regional and global sustainability, yet a robust and systematic way to quantify this impact is lacking. Here we introduce two complementary approaches to bridge this key methodological gap. The first entails constructing a new sustainability index capable of systematically considering pertinent indicators of interdependencies and spillovers between countries. To minimize ambiguities associated with the aggregated index, the second approach establishes a spatial analysis framework, one designed to explicitly incorporate dimensions of interdependence and spillovers, along with buffer and multiplier effects, enabling us to distinguish and gage the impact of spatial interconnections on regional and global sustainability. Overall, the two approaches applied in tandem reinforce the joint principles of 'one Earth' and 'leaving no one behind', and can help to clarify countries' responsibilities in respect of global sustainable development.