Is There an Environmental Kuznets Curve for Sulfur?

The environmental Kuznets curve (EKC) hypothesis proposes that there is an inverted U-shape relation between environmental degradation and income per capita. Various explanations for this phenomenon have been put forward and some authors argue that important explanatory variables are omitted from conventional EKC estimates. Inclusion of these omitted variables is argued to increase the estimated "turning point" - the level of GDP per capita above which environmental degradation is declining. In this paper we use a new cross-section/time-series data base of sulfur emissions for a wide range of developed and developing countries. The methodology involves estimating EKCs for subsets of this database as well as for the sample as a whole. The results show that estimating an EKC using data for only the OECD countries, as has often been the case, leads to estimates where the turning point is at a much lower level than when the EKC is estimated using data for the World as a whole. The paper explores possible explanations of these results using Monte Carlo analysis, and other statistical tests.We conclude that the simple EKC model is fundamentally misspecified and that there are omitted variables which are correlated with GDP.