Testing the stationarity of CO2 emissions series in Sub-Saharan African countries by incorporating nonlinearity and smooth breaks

We examine the stationarity properties of per capita CO2 emissions for 35 countries in Sub-Saharan Africa covering the period of 1960–2009. For this examination, we use a nonlinear time series and panel unit root tests. Becker et al.’s (2006) test statistic demonstrates that nonlinearity exists in our data and hence should be incorporated in a test for the unit root. Further, Becker et al.’s (2006) test shows evidence of mean reversion in the per capita CO2 emissions for 27 of the countries in Sub-Saharan Africa. However, when we use a panel unit root test with a SPSM procedure, we find that the per capita CO2 emissions for 15 of these countries are stationary. Moreover, when we add a Fourier function to the panel unit root test, we find evidence of stationarity in the per capita CO2 emissions series for all of the 35 countries analyzed.