The identification of average causal effects of a treatment in observational studies is typically based either on the unconfoundedness assumption or on the availability of an instrument. When available, instruments may also be used to test for the unconfoundedness assumption (exogeneity of the...

This paper investigates the relationship between urbanization and CO2 emissions in a sample of 20 emerging countries over the period 1992–2008 using the semi-parametric panel data model with fixed effects, proposed by Baltagi and Li (2002). We find little evidence in support of an inverted-U...