Kaya identity

The Kaya identity is a mathematical identity stating that the total emission level of the greenhouse gas carbon dioxide can be expressed as the product of four factors: human population, GDP per capita, energy intensity (per unit of GDP), and carbon intensity (emissions per unit of energy consumed).

[1][2] It is a concrete form of the more general I = PAT equation[3] relating factors that determine the level of human impact on climate.

Although the terms in the Kaya identity would in theory cancel out, it is useful in practice to calculate emissions in terms of more readily available data, namely population, GDP per capita, energy per unit GDP, and emissions per unit energy.

It is a variation of Paul R. Ehrlich & John Holdren's I=PAT formula that describes the factors of environmental impact.

Population growth projections are available independently from demographic research; GDP per capita trends are available from economic statistics and econometrics; similarly for energy intensity and emission levels.