Liu and Wu extend urban metabolism from flow accounting toward a thermodynamic theory of urban ecological scaling. Their central proposition is that urban ecosystems display patterned relations between energy flow, transformity, mass gradients and scale, and that shifts between system states can therefore be read as transformations in scaling behaviour. The review assembles evidence from socioeconomic scaling, energy metabolism, ecological networks and allometric theory to propose a unified hypothesis of multistable urban ecological states. Rather than treating urbanisation as simple growth, the authors describe it as a dynamic competition between ecological and socioeconomic systems for space, energy and output efficiency. Methodologically, scaling laws become diagnostic instruments for identifying transitions, disequilibria and possible ecological tipping points. The wider significance is conceptual: the city becomes a nonlinear energetic system whose apparent stability is produced by continual conversion and reorganisation. This creates a precise bridge between thermodynamics, complexity theory and urban ecology, and offers a vocabulary for describing urban change as state transition rather than as a merely morphological sequence.
URBANISM MEETS ART