Triptych sectoral CO2 emissions	Triptych sectoral per capita CO2 emissions
		unit: Mg C/yr (Megagram (1000 kg) of C per capita per year) dimension: region, triptych sectors
	unit: Pg C/yr (Petagram of C per year) dimension: region, triptych sectors

The Triptych approach is a sector-oriented approach used for supporting decision-making on international burden sharing or differentiation of future commitments in the European Union (EU) prior to Kyoto (COP-3) (Blok et al., 1997).

In this bottom-up approach different rules for differentiation of future commitments are applied to different sectors (e.g., convergence of per capita emissions in the domestic sector, efficiency and de-carbonization targets for the industrial and the power generation sector as described by den Elzen et al. (1999)).

In the triptych approach three sectors are distinguished:

1. Domestic sectors, which comprise the residential sector, the commercial sector, and sectors for transportation, light industry and agriculture.
2. Industrial sectors, which comprise internationally oriented industries where competitiveness is determined by the costs of energy and of energy efficiency measures. These are heavy industry, which comprises the building materials industry, and the chemical, iron and steel industry, non-ferrous metals, pulp and paper industries, refineries, coke ovens, gasworks and other energy transformation industries (excluding electricity generation). Compared to other economic sectors the industrial sector, especially the heavy industry, has a relatively high energy : value added ratio, and in most countries also a high ratio CO2 emission : value added. Hence, countries and regions with a high share of heavy industry have higher CO2 emissions per unit of GDP than countries that focus primarily on light industry and services. Setting CO2 emission targets on a per capita basis would therefore be a disadvantage for countries with a high share of such industries. Specific de-carbonization target rules for this sector could take these considerations into account.
3. Electricity generation sectors. There are important differences between regions and countries in the (fossil)-fuel mix and in the share of power production techniques such as nuclear power and renewables. The potential for renewable energy is different for each region, just like the public acceptance of nuclear energy.

In our calculations the emissions from light-industry are included in the industrial emissions. This is not in line with the original definition. However, the difference is minor because the contribution of light industry to the CO2 emissions of the industry-sector is small.

The triptych approach is also implemented in the FAIR model (Framework to Assess International Regimes for differentiation of future commitments). This interactive model was designed to quantitatively explore a range of alternative climate policy options for international differentiation of future commitments and link these to targets for global climate protection (den Elzen et al., 2001) and can be downloaded from http://www.rivm.nl/FAIR/.