Energy intensity and economic performance: A semi-systematic review of historical dynamics, determinants, constraints, and future research pathways

Energy intensity, commonly defined as energy use per unit of economic output, is widely used to assess efficiency improvements and progress toward decoupling. However, its interpretation is complicated by the fact that energy intensity is a composite, context-dependent indicator shaped by technological, structural, behavioral, infrastructural, and biophysical factors. This semi-systematic review synthesizes evidence from 147 studies across economics, engineering, industrial ecology, and biophysical analysis to clarify the drivers and limits of historical intensity trends. The review shows that observed declines often reflect structural change, sectoral reallocation, fuel switching, offshoring, and accounting conventions rather than genuine efficiency improvements. Rebound effects, infrastructural lock-in, material stock accumulation, and thermodynamic constraints further limit the potential for sustained long-term reductions. These mechanisms collectively elucidate why energy intensity cannot be regarded as a direct indicator of efficiency or as credible evidence of prospective decoupling. Building on this insight, the paper develops an integrated conceptual framework that links macroeconomic intensity dynamics with embodied energy, behavioral feedback, infrastructural inertia, and physical limits. This framework provides a more robust foundation for interpreting intensity-based indicators in modeling and policy contexts, particularly in scenarios that extrapolate past trends. The review also identifies several research priorities. Future research ought to amalgamate decomposition analysis with stock-based and material-flow methodologies, internalize rebound and behavioral feedback within macro-energy models, enhance multi-scale accounting of embodied energy and offshoring, and integrate biophysical constraints into long-term scenario formulation. Advancing these directions will strengthen the interpretive value of energy intensity and support more realistic assessments of long-term energy–economy pathways.