Measuring Sustainability at the Climate-Energy Nexus

Abstract

Balancing climate change mitigation, secure and affordable energy supply, and sustained economic activity remains a major sustainability challenge. This study introduces the Climate–Energy Sustainability Index (CESI), a composite indicator that captures six normalized dimensions: adjusted net savings, carbon emissions per capita, carbon intensity of energy use, renewable energy share, energy use per capita, and climate stability measured through temperature anomalies. CESI employs geometric-mean aggregation to enforce non-substitutability across dimensions and to penalize unbalanced development paths. Mathematically, the index remains within a fixed range. The direction of the normalized component scores is preserved. It also shows conditional scale invariance under the given normalization framework. The index is applied to 76 countries over the period 1990–2023. The results reveal substantial cross-country and regional heterogeneity in climate–energy sustainability outcomes. The global average CESI shows a gradual long-term increase, although the trajectory is non-linear and marked by periodic fluctuations. Cross-country dispersion changed over time. It increased from 1993 to 2013 but declined by 2023. This shows a recent reduction in dispersion, rather than consistent long-term convergence. Europe shows the strongest regional performance. Its performance is also more consistent over time. South America performs relatively well, but its results vary more over time. Africa, Asia, and Oceania show weaker progress, with some variation across the years. At the country level, Italy, Panama, Chile, the United Kingdom, and Japan emerge as the top performers in 2023. Tuvalu, Trinidad and Tobago, and several African and small-island states remain at the lower end of the distribution. Scatter-plot analysis indicates that no single factor determines CESI performance. Adjusted net savings and renewable energy share show weak positive relationships with CESI, suggesting that greater savings or renewable deployment alone does not guarantee better sustainability outcomes. Energy use per capita, carbon intensity, and per capita CO? emissions display weak negative associations. Climate–energy sustainability depends on the combined interaction of cleaner energy structure, efficient energy use, and lower carbon dependence rather than improvement in any single indicator. CESI captures observed sustainability outcomes rather than policy effort or transition readiness. As a result, similar index values may reflect different development pathways.