Three Lessons From Trends in CO2 Emissions and Energy Use in the United States

I derive three lessons about the potential to reduce CO2 emissions in the United States by analyzing data on CO2 emissions and energy use from 1960 to 2003. First, improvements in the energy efficiency of the economy and reductions in the CO2 intensity of the energy supply did not lead to a decline in CO2 emissions but rather were associated with rising CO2 emissions. Second, the decline in the CO2 intensity of the energy supply was primarily due to the expansion of nuclear power, which is not environmentally benign. There is no free lunch with regard to non- and low-carbon energy sources, since all energy sources generate some environmental impacts. Furthermore, expanding the use of non-fossil-fuel energy sources does not necessarily suppress the use of fossil-fuel energy sources. Third, population growth has been a key factor driving the expansion of national CO2 emissions and energy use, particularly since per capita levels stabilized after the 1970s.