Abstract
This study investigates the Environmental Kuznets Curve (EKC) hypothesis, which posits an inverted-U relationship between economic growth and environmental degradation, for three economies at different stages of development: Bangladesh, China, and Germany. Using annual data on carbon dioxide (CO₂) emissions per capita and real GDP per capita over the period 1990–2024, drawn from the World Bank World Development Indicators, the study estimates a quadratic-in-income specification in which the logarithm of CO₂ emissions per capita is regressed on the logarithm of real GDP per capita and its square. The model is estimated separately for each country by ordinary least squares and jointly in a pooled panel with country fixed effects. The pooled results support the EKC hypothesis: the squared income term is negative and statistically significant (β₂ = − 0.225, p < 0.001), implying an income turning point of approximately US$14,500. The country-level estimates reveal a coherent development-stage pattern. Germany lies on the declining arm of the curve, with emissions falling as income rises; China is at or close to its emissions peak; and Bangladesh remains on the early rising arm, approaching an estimated turning point. These findings indicate that economic growth is not uniformly detrimental to air quality, but that the timing and height of the turning point depend on a country's development stage, energy mix, and policy environment. Policy implications for renewable energy investment, carbon pricing, and sustainable urbanization are discussed.