To better understand how carbon emission reduction is achieved across different models, emission growth is typically decomposed into different components. One of many ways to do the decomposition is to break emissions growth into fuel switching, energy intensity, and economic growth components. To characterize the fuel switching effect, the emission intensity (emission/energy ratio) is used. The total primary energy equivalent is used as a consistent energy consumption definition. A smaller emission intensity means more intensive use of lower carbon-emitting energy, thus a bigger switching effect. The energy intensity effect can similarly be measured by the energy intensity (energy/GDP ratio). A smaller energy intensity indicates a combination of less energy use within industries and sectoral shift away from energy intensive industries. GDP is used as the economic growth index.