Kaya identity
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The Kaya identity is an idealized equation describing what factors determine the level of human impact on climate, in the form of emissions of the greenhouse gas carbon dioxide. It stipulates that total emission level depends on the product of four inputs: population times GDP per capita times energy use per unit of GDP times emissions per unit of energy consumed.
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[edit] Overview
The Kaya identity was developed by Japanese energy economist Yoichi Kaya. It is the subject of his book Environment, Energy, and Economy: strategies for sustainability co-authored with Keiichi Yokobori as the output of a conference entitled Energy, and Economic Development (1993 : Tokyo, Japan) Tokyo Conference on Global Environment. The identity is expressed in the form:
F = P * (G/P) * (E/G) * (F/E) = P * g * e * f
where F is global CO2 emissions from human sources, P is global population, G is world GDP, E is global primary energy consumption, g = (G/P) is global per-capita GDP, e=(E/G) is the energy intensity of world GDP, and f=(F/E) is the carbon intensity of energy. (Extensive variables are uppercase while intensive variables are lowercase.)
[edit] Use in IPCC reports
The Kaya identity plays a core role in the development of future emissions scenarios in the IPCC Special Report on Emissions Scenarios link. The scenarios set out a range of assumed conditions for future development of each of the four inputs. 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.
[edit] Use in other scientific analysis
The Kaya identity is reviewed in P. E. Waggoner and J. H. Ausubel, A framework for sustainability science: A renovated IPAT identity, PNAS 99 (12): 7860 (2002) link to article PDF
The article Global and regional drivers of accelerating CO2 emissions by MR Raupach et al. [PNAS 10.1073 online early access, May 22, 2007], link to article PDF uses the Kaya Identity in its analysis of recent trends in carbon emissions, and finds:
... cessation or reversal of earlier declining trends in the energy intensity of gross domestic product (GDP) (energy/GDP) and the carbon intensity of energy (emissions/energy), coupled with continuing increases in population and per-capita GDP. Nearly constant or slightly increasing trends in the carbon intensity of energy have been recently observed in both developed and developing regions. No region is decarbonizing its energy supply.
