The Kaya Identity provides an intuitive approach to the interpretation of historical trends and future projections of energy-related carbon dioxide emissions. It is used to describe the relationship among the factors that influ-ence trends in energy-related carbon dioxide emissions:
CO2= (CO2/E) × (E/GDP) × (GDP/POP) ×POP .
1990 2000 2007 2015 2025 2035
0 2 4 6 8 10
History Projections
OECD Non-OECD Figure 108. World carbon dioxide emissions from liquids combustion, 1990-2035
(billion metric tons)
1990 2000 2007 2015 2025 2035
0 1 2 3 4
5 History Projections
OECD
Non-OECD Figure 109. World carbon dioxide emissions from natural gas combustion, 1990-2035 (billion metric tons)
1990 2000 2007 2015 2025 2035
0 5 10 15
History Projections
OECD Non-OECD
Figure 110. World carbon dioxide emissions from coal combustion, 1990-2035
(billion metric tons)
The identity links total energy-related carbon dioxide emissions (CO2) to energy (E), the level of economic activity as measured by gross domestic product (GDP), and population size (POP). Conveniently, the percent-age rate of change in carbon emission levels over time approximates the sum of the percentage rate of change across the four components. The first two components on the right-hand side of the equation represent the carbon dioxide intensity of energy supply (CO2/E) and the energy intensity of economic activity (E/GDP).
When they are multiplied together, the resulting measure is carbon dioxide emissions per dollar of GDP (CO2/GDP)—i.e., the carbon intensity of the economy, which is another common measure used in analysis.
Economic output (GDP) is decomposed into output per capita (GDP/POP) and population (POP). At any point in time, the level of energy-related carbon dioxide emis-sions can be seen as the product of the four Kaya Identity components—energy intensity, carbon dioxide intensity of energy supply, output per capita, and population.33 Using 2007 data as examples, world energy-related car-bon dioxide emissions totaled 29.7 billion metric tons in that year, world energy consumption totaled 495 qua-drillion Btu, world GDP totaled $63.1 trillion, and the total world population was 6,665 million. Using those figures in the Kaya equation yields the following: 60.1 metric tons of carbon dioxide per billion Btu of energy (CO2/E), 7.8 thousand Btu of energy per dollar of GDP (E/GDP), and $9,552 of income per person (GDP/POP).
Of the four Kaya components, policymakers are most actively concerned with energy intensity of economic output (E/GDP) and carbon dioxide intensity of the energy supply (CO2/E), because they correspond to the policy levers most available to them. Reducing growth in per-capita output would also have a mitigating influ-ence on emissions, but governments generally pursue policies to increase rather than reduce output per capita to advance objectives other than greenhouse gas mitiga-tion. Some countries, such as China, have policies related directly to limiting population growth, but most countries pursue policies that only indirectly influence population growth.
Table 20 shows absolute regional Kaya Identity values for selected years and average annual rates of change for three 15-year periods: (1) an historical period from 1990
to 2005, (2) a period from 2005 to 2020, and (3) the final period of the IEO2010 projection from 2020 to 2035.34 The three periods show distinctive patterns of emissions growth and underlying Kaya factors.
Both OECD and non-OECD economies have experi-enced or are expected to experience declines in energy intensity. These are the only values that are consistently negative across all time periods at the aggregate level. In the historical period, only OECD Asia showed a rise in energy intensity, reflecting an increase in the energy intensity of Japan’s economy. However, Japan has the lowest energy intensity among all the fully industrial-ized OECD economies.
Carbon intensity varies across time and regions, but in no case does it change as much as energy intensity does.
Over the 1990-2005 period, the largest annual decline worldwide (0.7 percent) is for non-OECD Europe and Eurasia, where much of the old energy infrastructure was shut down and replaced after the fall of the Soviet Union. The next largest annual decline (0.6 percent) occurred in OECD Europe, where coal consumption fell from 17.7 quadrillion Btu in 1990 to 12.9 quadrillion Btu in 2005 and was replaced by natural gas consumption, which increased from 11.2 quadrillion Btu in 1990 to 19.8 quadrillion Btu in 2005. In many regions, including North America, the carbon intensity of energy supply remained largely unchanged from 1990 to 2005. For the entire world, carbon intensity declined by only 0.1 per-cent annually from 1990 to 2005, compared with a 1.5-percent average annual decline in energy intensity.
Over the period from 2005 to 2020, carbon intensity declines in theIEO2010Reference case in every part of the world. While explicit carbon policies, such as the caps in OECD Europe, are not included in the model, analysts’ judgment regarding, for example, nuclear power have taken those policies into account.35In other areas, declining carbon intensity is the result of policies such as renewable portfolio standards and other approaches to promote alternatives to fossil fuels. From 2020 to 2035, there is a slight decrease in carbon intensity of energy supply in OECD economies and a slight increase in non-OECD economies, so that there is virtu-ally no change on a worldwide basis in the absence of additional policies to stem emissions growth, which are not included in the Reference case.
130 U.S. Energy Information Administration / International Energy Outlook 2010
33In other analyses, EIA has combined output per capita and population as GDP, simplifying the right side of the equation to three com-ponents:GDP,E/GDPandC/E. However, because rates of output and population growth can differ dramatically across countries and re-gions, this analysis uses the more detailed equation. See U.S. Energy Information Administration,Emissions of Greenhouse Gases in the United States 2008, DOE/EIA-0573(2008) (Washington, DC, December 2009), p. 3, web site www.eia.gov/oiaf/1605/ggrpt/pdf/0573(2008).pdf.
34See Appendix J for a complete regional listing of Kaya Identity components.
35Greenhouse gas emissions caps in Europe are not explicitly included in theIEO2010analysis for the following reasons: (1) greenhouse gases other than energy-related carbon dioxide are included in the caps, but they are not modeled inIEO2010; (2) the regional composition of the European Union differs from the OECD Europe region modeled inIEO2010; (3) the European Union Emissions Trading System in-cludes offsets that involve countries outside the European Union; and (4) theIEO2010Reference case extends to 2035 and therefore would require further assumptions regarding emissions caps beyond the period covered under the Emissions Trading System.
For non-OECD countries, increases in output per capita, coupled with even moderate population growth, over-whelm the improvements in energy and carbon inten-sity. For example, the combined decrease in carbon intensity and energy intensity in non-OECD economies averages 3.0 percent per year from 2005 to 2020. With
output per capita rising by 4.3 percent per year and pop-ulation growing by 1.2 percent per year, however, the net increase in non-OECD carbon dioxide emissions is 2.3 percent per year.36 Over the same period, the com-bined decrease (improvement) in carbon intensity and energy intensity in OECD economies averages 2.1
Table 20. Kaya component values by region and country, 1990-2035
History Projections
Average annual percent change
1990 2005 2007 2020 2035
1990-2005
2005-2020
2020-2035 Carbon intensity (metric tons per billion Btu)
OECD . . . . 57.7 55.8 55.7 51.7 50.6 -0.2 -0.5 -0.1
North America . . . 57.0 57.3 56.7 53.4 52.7 0.0 -0.5 -0.1
Europe . . . 58.5 53.4 53.3 48.7 46.6 -0.6 -0.6 -0.3
Asia . . . 58.2 56.5 57.3 52.6 51.6 -0.2 -0.5 -0.1
Non-OECD . . . . 64.0 64.2 64.2 61.4 61.6 0.0 -0.3 0.0
Europe/Eurasia . . . 63.0 56.4 56.3 53.8 52.7 -0.7 -0.3 -0.1
Asia . . . 74.3 74.5 74.1 69.1 68.5 0.0 -0.5 -0.1
Central and South America . . . . 42.1 42.0 41.7 39.7 37.9 0.0 -0.4 -0.3
Energy intensity (thousand Btu per 2005 U.S. dollars of GDP)
OECD . . . . 8.5 7.1 6.8 5.5 4.4 -1.2 -1.7 -1.5
North America . . . 10.5 8.2 7.9 6.2 4.7 -1.6 -1.9 -1.8
Europe . . . 7.3 5.9 5.5 4.6 3.7 -1.4 -1.7 -1.4
Asia . . . 6.7 7.0 6.8 5.9 5.4 0.4 -1.2 -0.6
Non-OECD . . . . 12.6 10.0 9.3 6.6 5.1 -1.5 -2.8 -1.7
Europe/Eurasia . . . 20.9 16.9 14.8 11.0 8.1 -1.4 -2.9 -2.0
Asia . . . 11.6 9.5 8.9 5.9 4.7 -1.3 -3.1 -1.5
Central and South America . . . . 7.2 7.2 6.9 5.6 4.4 0.0 -1.7 -1.5
Output per capita (2005 U.S. dollars of GDP per person)
OECD . . . . 22,889 29,440 30,745 36,416 47,292 1.7 1.4 1.8
North America . . . 26,887 34,472 35,554 42,032 54,766 1.7 1.3 1.8
Europe . . . 20,280 26,030 27,427 31,923 41,234 1.7 1.4 1.7 Asia . . . 21,909 27,697 29,140 35,078 43,460 1.6 1.6 1.4 Non-OECD . . . . 2,907 4,282 4,897 8,085 12,654 2.6 4.3 3.0
Europe/Eurasia . . . 9,266 8,722 10,227 14,719 22,978 -0.4 3.5 3.0
Asia . . . 1,537 3,452 4,063 7,917 13,419 5.5 5.7 3.6
Central and South America . . . . 6,370 8,001 8,757 11,827 16,998 1.5 2.6 2.4
Population (millions)
OECD . . . . 1,025 1,167 1,183 1,267 1,342 0.9 0.6 0.4
North America . . . 359 432 441 500 569 1.2 1.0 0.9
Europe . . . 479 535 541 565 577 0.7 0.4 0.1
Asia . . . 187 200 201 202 196 0.4 0.1 -0.2
Non-OECD . . . . 4,253 5,332 5,467 6,343 7,127 1.5 1.2 0.8
Europe/Eurasia . . . 347 341 340 336 324 -0.1 -0.1 -0.2
Asia . . . 2,780 3,446 3,525 4,021 4,398 1.4 1.0 0.6
Central and South America . . . . 358 451 464 538 606 1.6 1.2 0.8
36Simply summing the rates of change over time often introduces an error factor of 0.1 to 0.2 percentage points.
percent per year—lower than in non-OECD econo-mies—but because OECD output per capita increases by 1.4 percent per year and population growth averages 0.5 percent per year, the net result is that OECD carbon dioxide emissions decline by an average of 0.2 percent per year.