The Environmental Kuznets Curve: Real Progress or Misspecified Models?

We explore the importance of modeling strategies when estimating the emissions-income relationship. Using U.S. state-level panel data on nitrogen oxide and sulfur dioxide emissions, we estimate several environmental Kuznets curves using the standard parametric framework as well as a more flexible semiparametric alternative. Formal statistical comparisons of the results overwhelmingly reject the parametric approach. Moreover, the differences, particularly for sulfur dioxide, are economically significant. © 2003 President and Fellows of Harvard College and the Massachusetts Institute of Technology.