### Trend (KAYA)

#### Indicators:

KAYA Population GDP per Capita Energy intensity Carbon factor CO2 emissions from energy use | Energy determinants

The Kaya indicators consist of the four factors of the so-called Kaya identity. In the Kaya identity, carbon emissions are formulated as the product of population, GDP per capita, energy use per unit of GDP (i.e., energy-intensity) and carbon emission per unit of energy (i.e., carbon factor) as follows:

In the User Support System, the four factors and the resulting carbon dioxide emissions have been indicated in the same way as indicated in the above formula. The upper set of five graphs shows the factors in absolute numbers. The lower set shows the annual changes in each of them. The latter show the moving average values, which have been determined independently - which means that adding the changes in each of the factors not always gives the exact changes in carbon emissions for each year. Long-term trends are correct, however.

| #### Population
| unit: million persons dimension: region

The population view shows the historical (1971-2000) and projected (2000-2100) human population for each of the 24 regions and for the world. Historical population data are based on the United Nations. The scenario projections are based on the Special Report on Emissions Scenarios (SRES) (see also the population indicators).

| #### Gross domestic product per capita
| unit: 1000 US$ (1995)/yr (thousand 1995-US$ per year) dimension: region

Gross domestic product (GDP) per capita is the ratio of regional gross domestic product (GDP) and population. It is presented for the historical (1971-2000) and projected (2000-2100) periods for each of the 24 regions and for the world. Historical data are based on the World Bank and aggregated interregional data. The scenario projections are based on simulations with the WorldScan-model (see also economic indicators).

| #### Energy intensity
| unit: GJ/US$ (1995) (Gigajoule per 1995-US dollars) dimension: region

Energy intensity is the ratio between primary energy use and gross domestic product (GDP). It is presented for each region and the world. For the industrialized regions it tends to decline for the time period considered. This is the result of, among others, the structural change from industrial to service- and information-oriented activities, efficiency improvements and saturation tendencies. In the less industrialized regions this decline is also expected also on the long-run but possibly only after an initial rise as a result of ongoing industrialization.

Energy intensity should not be confused with energy efficiency. The relationship between monetary economic activities as measured in GDP and physical energy flows is a complex one. If basic industrial processes such as mining, steel and petrochemicals manufacturing and freight transport make up a large part of GDP, energy intensity will be high. If knowledge and information-intensive sectors contribute strongly to GDP, energy intensity is lower - partly because the energy incorporated in the non-energy imports is not accounted for .

| #### Carbon factor
| unit: kg C /GJ (kilogram C per Gigajoule) dimension: region

The carbon factor indicates the amount of carbon released per unit of primary energy consumption (where 1.0 kg Carbon equals 3.7 kg carbon dioxide) for each region and the world. The higher the share of high-carbon content fuels in total energy consumption, the higher the carbon factor. In case of a full transition to renewable energy sources, such as wind and hydropower, the carbon factor will be equal to zero.

The amount of carbon dioxide (CO2) emitted per GJ of energy consumption strongly differs among the various energy carriers. In the TIMER model, the carbon factor is calculated on the basis of information contained in the matrix 'total primary energy supply', using the following carbon-contents:

- coal: 25.5 kg C/GJ
- crude oil: 19.3 kg C/GJ
- natural gas 15.3 kg C/GJ

With regard to biofuels (both traditional and modern) it is assumed that net carbon emissions to the atmosphere are zero.

| #### CO2 emissions from energy use
| unit: Pg C/yr (Petagram C per year) dimension: region

CO2 emissions from energy use specify the energy-related CO2 emissions for each region and the world as a whole. Energy use forms one of the most important sources of CO2 emissions (see also emission indicators).

| #### Energy determinants
| unit: none (1971=0) dimension: region, sector, energy function, determinants

The energy determinants indicate for each sector and energy function how the demand for secondary energy carriers is built up in a region. The graph has to be read as a sequence of curves, showing how activity leads to useful energy demand, is influenced by sectoral changes, is lowered by conservation and changed by fuel switches. Each of the determinants has been expressed as the power-10 logaritm of the index between its value and its value in 1971.This gives a good indication of the changes of this determinant since 1971. The determinants of secondary energy use are:

- increase of activity levels. Activity levels in the model are measured in monetary units. Several proxies are used to determine changes in activity levels for each sector. For the industrial sector, the activity indicator is industrial value added; for the transport sector it is GDP; for the residential sectors it is private consumption; for the services sector it is services value added; for the other sectors it is GDP; and, finally, for the economy as a whole it is GDP.
- sectoral change (only relevant for the economy as a whole). Sectoral change indicates the impacts of changes in the shares of the five sectors in total energy use for the 'energy intensity' of the economy as a whole.
- effect from structural change (intersectoral shifts) and life-style changes. Structural change indicates the impact of changes in the mix of products/processes in each sector, such as shifts from light to heavy industry or from road truck to train in freight transport.
- energy conservation (energy efficiency improvement). Energy conservation accounts for investments in energy efficiency improvement and includes price-induced and autonomous trends.
- fuel switch. The changes shown for 'fuel switch' reflect the different end-use efficiencies of different fuels. For example, most energy services can be provided with less GJ/unit by natural gas than by coal.

The last four factors together determine energy intensity. Sectoral energy demand in the form of secondary fuels and electricity is the product of energy intensity and sectoral activity.