They find that the elasticity of CO2 emissions and energy are close to unity (., a 1% increase in population leads to an approximately 1% increase in CO2 emissions). They do not estimate how these elasticities may vary with population levels. All of these results are based on cross-sectional data for 1 year only. Finally, Shi (2003), again in the context of the IPAT model, uses a panel of cross-sectional and time series data. Shi finds population elas- ticities for CO2 of between and , depending on the model used, but does not examine how these may vary with different population levels. While a step in the.
