The changing mix of fossil fuels used and the related evolution of CO2 emissions

To limit global climate change, ultimately it will be necessary to minimize the use of all fossil fuels for energy. Because the rate of CO2 emissions per unit of primary energy varies among the fossil fuels, it is useful to focus first on reducing the use of coal, the fuel with the most CO2 per unit of energy used. Although multiple factors are involved in the choice of which fuel will be used for a given purpose, data on CO2 emissions show that over the last 25 years there has been an evolution in the fraction of emissions away from coal and toward natural gas. That is, although total emissions have continued to increase globally, the fraction attributable to coal has been decreasing in many places. This is true for the global sum of emissions, for Annex I countries, and for all regions except Asia Pacific. The fraction of emissions from oil products has varied largely with growth in the contribution of petroleum transportation fuels. Focus on decreasing the sum of all fossil fuels is needed, especially among the major energy users in the Asia Pacific region, but progress in the decreasing relative use of coal is promising.