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6.1 Background

The objective of the United Nation Framework Convention on Climate Change (UNFCCC) is to stabilise greenhouse gas concentrations to avoid dangerous anthropogenic interference with the climate system. This target is formulated in Article 2 of the UNFCCC [UNFCCC 1992], which is accepted by nearly all countries in the world.

Several countries, including the European Union (EU), and many environmental non-governmental organisations have agreed that global average temperature increase should be limited to 2°C above pre-industrial levels to avoid such dangerous interference. As early as 1996, the Council of Ministers of the EU agreed that “global average temperatures should not exceed 2 degrees Celsius above pre-industrial level and that therefore concentration levels lower than 550 ppm CO2 should guide global limitation and reduction efforts” [EU Council 1996]. The target of 2°C has been reaffirmed subsequently as the EU’s submissions to the international negotiation processes in 2006 ([UNFCCC 2006a, 2006b]). The EU states that it “will require global greenhouse gas emissions to peak within the next two decades, followed by substantial reductions in the order of at least 15% and perhaps by as much as 50% by 2050 compared to 1990 levels.

”The reduction of global emissions by 2050 will have to be achieved differentiated between countries based on their different responsibilities for climate change and different mitigation capabilities. Developed countries that have contributed most to historical emissions will have to reduce emissions substantially. Developing countries may increase emissions for a defined period and would later also reduce emissions. Accordingly, industrialised countries’ will have to reduce emission by -70% to -90% in 2050 compared to their 1990 emissions to meet the 2°C target ([den Elzen and Meinshausen 2005]; [Höhne et al. 2005]).

It is likely that emissions in the building sector will have to be reduced more than the average over all sectors. Emission reduction costs and capabilities differ among sectors. The International Panel on Climate Change (IPCC) is the most important scientific advisory body to the UNFCCC. Its third assessment report [IPCC 2001] identified emission reduction costs until 2020. For many developed countries these costs were estimated to be up to 200 US $ per ton of carbon avoided for a number of sectors, e.g. transport, energy supply and agriculture. Especially for the building sector estimated emission reduction costs are mainly negative which means that they can save up to 400 US $ per ton of carbon avoided until 2020 [IPCC 2001]. The cost effectiveness of the CO2 mitigation measures in the building stock were confirmed in several reports ([Ecofys 2004], [Ecofys 2005]). The high reduction potentials and the cost efficient reduction measures require the building sector to realise an emission reduction share above average compared to the other sectors. Assuming that the target for the industrial countries should be 80% and taking into account that the EU-building stock will further increase in the next years, it is assumed that the building sector has to contribute with 85% CO2-emission-savings until 2050 referred to 1990.

At the same time, the foreseen development of the fuel mix for space heating purposes (for example switching from coal and oil to gas and increasing the share of biomass and other renewables, see Figure 37) and the increase in system efficiency compared to 1990 (e.g. condensing boilers) will result in an improvement of the CO2-emission factor for households of about 19%. This leads to an average of 82% to be saved on energy demand for space heating (7).

The fuel mix according to the PRIMES-scenario is shown in the graph below.

 

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7 The assumed improvement of the CO2 emission factor results in a relatively small change of the saving target from 85% to 82%. This is caused by the application of the improved emission factor on a high overall saving objective. Mathematically it results from following calculation: 1 - (1-85%)/(1-18.8%) = 81,53%