This graph depicts the changes in carbon dioxide (CO₂) emissions over time as a function of five driving forces: 1) the amount of CO₂ produced per unit of energy (CO₂ intensity); 2) the amount of energy used per unit of gross domestic product (energy intensity); 3) structural changes in the economy; 4) per capita income; and 5) population. Although CO₂ intensity and especially energy intensity have decreased significantly and the structure of the U.S. economy has changed, total CO₂ emissions have continued to rise as a result of the growth in both population and per capita income. (Baldwin and Sue Wing, 20134ae74fe5-51c5-4235-b9ab-3648489a2d9c).