Estimating different order polynomial logarithmic environmental Kuznets curves.

This paper contributes to the environmental literature by (i) demonstrating that the estimated coefficients and the statistical significance of the non-leading terms in quadratic, cubic, and quartic logarithmic environmental Kuznets curve (EKC) specifications are arbitrary and should therefore not be used to choose the preferred specification and (ii) detailing a proposed general-to-specific type methodology for choosing the appropriate specifications when attempting to estimate higher-order polynomials such as cubic and quartic logarithmic EKC relationships. Testing for the existence and shape of the well-known EKC phenomenon is a hot topic in the environmental economics literature. The conventional approach widely employs quadratic and cubic specifications and more recently also the quartic specification, where the variables are in logarithmic form. However, it is important that researchers understand whether the estimated EKC coefficients, turning points, and elasticities are statistically acceptable, economically interpretable, and comparable. In addition, it is vital that researchers have a clear structured non-arbitrary methodology for determining the preferred specification and hence shape of the estimated EKC. We therefore show mathematically and empirically the arbitrary nature of estimated non-leading coefficients in quadratic, cubic, and quartic logarithmic EKC specifications, being dependent upon the units of measurement chosen for the independent variables (e.g. dependent upon a rescaling of the variables such as moving from $m to $bn). Consequently, the practice followed in many previously papers, whereby the estimates of the non-leading terms are used in the decision to choose the preferred specification of an estimated EKC relationship, is incorrect and should not be followed since it potentially could lead to misleading conclusions. Instead, it should be based upon the sign and statistical significance of the estimated coefficients of the leading terms, the location of turning point(s), and the sign and statistical significance of the estimated elasticities. Furthermore, we suggest that researchers should follow a proposed general-to-specific type methodology for choosing the appropriate order of polynomials when attempting to estimate higher-order polynomial logarithmic EKCs.

Correction to: Does CO2 emissions-economic growth relationship reveal EKC in developing countries? Evidence from Kazakhstan.

The article Does CO2 emissions-economic growth relationship reveal EKC in developing countries? Evidence from Kazakhstan, written by Fakhri J. Hasanov, Jeyhun I.

Correction to: Re-evaluating the environmental impacts of tourism: does EKC exist?

The article Re-evaluating the environmental impacts of tourism: does EKC exist?, written by Jeyhun I. Mikayilov, Shahriyar Mukhtarov, Jeyhun Mammadov and Mayis Azizov.

Does CO2 emissions-economic growth relationship reveal EKC in developing countries? Evidence from Kazakhstan.

This paper investigates the CO2 emissions-economic growth relationship in Kazakhstan for the period 1992-2013. Johansen, ARDLBT, DOLS, FMOLS, and CCR cointegration methods are used for robustness purpose. We start with the cubic functional form to rule out any misleading results that can be caused by misspecification. Although the estimation results suggest "U"-shaped relationship, the turning point of income is out of the period. It means that the impact of economic growth on CO2 is monotonically increasing in the long run indicating the Environmental Kuznets Curve (EKC) hypothesis does not hold for Kazakhstan. Moreover, we calculate that the income elasticity of CO2 is about unity. The paper concludes that the Kazakhstani policymakers should focus on less energy-intensive sectors as well as using more renewable energy in order to avoid higher pollution effects of economic growth. They may also set new policy regulations for CO2 reduction.

Re-evaluating the environmental impacts of tourism: does EKC exist?

The study investigates the long-run impact of tourism development on ecological footprint by employing the time-varying coefficient cointegration approach (TVC), in addition to the conventional cointegration techniques in the case of Azerbaijan for the period of 1996-2014. Based on the TVC estimation results, the coefficient of tourism development, which is the income elasticity of environmental degradation, was found to be time invariant. The paper uses energy consumption, trade, urbanization, and institutional quality indicators as control explanatory variables. The estimation results revealed that trade and energy consumption have statistically significant and positive impact on ecological footprint, while the coefficients of the other explanatory variables were found to be insignificant. Both the conventional estimation methods and the TVC concluded that, for the relationship between ecological footprint and tourism development, the EKC hypothesis is not present in Azerbaijan. Policy implications for the resource-rich economies have been discussed.