This paper explores the importance of differential output growth across regions within a country in reducing the country's total carbon dioxide emissions from the combustion of fossil fuels. It proposes a framework that decomposes changes in emissions into sources attributable to 1) national growth rate of gross domestic product (GDP), 2) differential GDP growth across regions, 3) changes in energy intensity, and 4) changes in CO2 emission coefficient of energy. Data for China (1995-2009) and the United States (1990-2009) are analyzed. Uneven growth across regions reduced carbon dioxide emissions in both countries. (C) 2013 Elsevier Ltd. All rights reserved.