Carbon dioxide (CO2) emissions intensity—the level of CO2 emissions per unit of economic output—varies widely across countries, reflecting differences in economic structure, energy efficiency, and fuel mix. For example, among the major emitters, CO2 intensity varies almost sixfold—from 204 tonnes per million international dollars (PPP) gross domestic product (GDP) in France, to 1,124 tonnes in Ukraine.

Over time, intensity levels decline in most countries because GDP usually increases at a faster rate than emissions, though emissions intensities are not directly correlated with changes in activity levels (GDP and population). Even in the event of major GDP changes, changes in intensity levels may be modest.