Kaya identity

The Kaya identity is an equation relating factors that determine the level of human impact on climate, in the form of emissions of the greenhouse gas carbon dioxide. It states that total emission level can be expressed as the product of four inputs: population, GDP per capita, energy use per unit of GDP, emissions per unit of energy consumed.

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 and g = (G/P) is global per-capita GDP, :E is global primary energy consumption and 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.

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 [http://www.grida.no/climate/ipcc/emission/038.htm 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.

Use in other scientific analysis

The Kaya identity is reviewed in P. E. Waggoner and J. H. Ausubel, "A framework for sustainability science: A renovatedIPAT identity", "PNAS" 99 (12): 7860 (2002) [http://www.pnas.org/cgi/reprint/99/12/7860 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] , [http://www.pnas.org/cgi/reprint/0700609104v1 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.

External links

* [http://www.manicore.com/anglais/documentation_a/greenhouse/kaya_equation.html Climate change - what is Kaya's equation]
* http://www.worldchanging.com/archives/002952.html
* http://www.computare.org/Support%20documents/Fora%20Input/CCC2006/Sustainable%20Paper%2006_05.htm
* http://www.realclimate.org/index.php?p=164
* [http://geosci.uchicago.edu/~archer/cgimodels/kaya.html Online 'Kaya Calculator']