|Working Group III: Mitigation|
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This section addresses greenhouse gas emissions and emissions reduction opportunities for residential and commercial (including institutional) buildings, often called the residential and service sectors. Carbon dioxide emissions from fossil fuel energy used directly or as electricity to power equipment and condition the air (including both heating and cooling) within these buildings is by far the largest source of greenhouse gas emissions in this sector. Other sources include HFCs from the production of foam insulation and for use in residential and commercial refrigeration and air conditioning, and a variety of greenhouse gases produced through combustion of biomass in cookstoves.3.3.2 Summary of the Second Assessment Report
The Second Assessment Report (SAR) reviewed historical energy use and greenhouse gas emissions trends as well as mitigation options in the buildings sector in Chapter 22, Mitigation Options for Human Settlements (Levine et al., 1996a). This chapter showed that residential and commercial buildings accounted for 19% and 10%, respectively, of global carbon dioxide (CO2) emissions from the use of fossil fuels in 1990. More recent estimates increase this percentage to 21% for residential buildings and 10.5% for commercial buildings, both for 1990 and 1995, as shown in Table 3.1. Globally, space heating is the dominant energy end-use in both residential and commercial buildings. Developed countries account for the vast majority of buildings-related CO2 emissions, but the bulk of growth in these emissions over the past two decades was seen in developing countries. The SAR found that many cost-effective technologies are available to reduce energy-related CO2 emissions, but that consumers and decision-makers often do not invest in energy efficiency for a variety of reasons, including existing economic incentives, levels of information, and conditions in the market. The SAR concluded that under a scenario with aggressive adoption of energy-efficiency measures, cost-effective energy efficiency could likely cut projected baseline growth in carbon emissions from energy use in buildings by half over the next two decades.3.3.3 Historic and Future Trends
CO2 from energy use is the dominant greenhouse gas emitted in the buildings sector, followed by HFCs used in refrigeration, air conditioning, and foam insulation, and cookstove emissions of methane and nitrous oxide (see Table 3.2). Developed countries have the largest emissions of CO2 and HFCs, while developing countries have the largest emissions of greenhouse gases from non-renewable biomass combustion in cookstoves (Smith et al., 2000). It is noted, however, that the biomass energy source is being replaced with non-renewable carbon-based fuels (Price et al., 1998). This trend is expected to continue.
Energy use in buildings exhibited a steady growth from 1971 through 1990 in all regions of the world, averaging almost 3% per year. Because of the decline in energy use in buildings in the former Soviet Union after 1989, global energy use in buildings has grown slower than for other sectors in recent years. Growth in commercial buildings was higher than growth in residential buildings in all regions of the world, averaging 3.5% per year globally between 1971 and 1990. Energy-related CO2 emissions also grew during this period. By 1995, CO2 emissions from fuels and electricity used in buildings reached 874MtC and 858MtC, respectively, for a total of 1732MtC, or 98% of all buildings-related GHG emissions. Growth in these CO2 emissions was slower than the growth in primary energy in both the developed countries and the rest-of-world region, most likely the result of fuel switching to lower carbon fuels in these regions. In contrast, growth in energy-related CO2 emissions in the developing countries Asia Pacific region was 6.3% per year between 1971 and 1995, greater than the 5.5% per year growth in primary energy use, reflecting a growing reliance on more carbon-intensive fuels in this region.6
Non-CO2 greenhouse gas emissions from the buildings sector are hydrofluorocarbons (HFCs)7 used or projected to be used in residential and commercial refrigerators, air conditioning systems, and in open and closed cell foam for insulation. HFCs in the building sector were essentially zero in 1995, but are projected to grow as they replace ozone-depleting substances (see Appendix to this chapter). In addition, methane (CH4), nitrous oxide (N2O), carbon monoxide (CO), and nitrogen oxides (NOx) (along with CO2) are produced through combustion of biomass in cookstoves (Levine et al., 1996b; Smith et al., 2000). It is estimated the biomass cookstoves emit about 40MtCeq, 2% of total buildings-related GHG emissions (Smith et al., 2000). These emissions are concentrated in developing countries, where biomass fuels can account for more than 40% of the total energy used in residences (UNDP, 1999).8
Key drivers of energy use and related GHG emissions in buildings include activity (population growth, size of labour force, urbanization, number of households, per capita living area, and persons per residence), economic variables (change in GDP and personal income), energy efficiency trends, and carbon intensity trends. These factors are in turn driven by changes in consumer preferences, energy and technology costs, settlement patterns, technical change, and overall economic conditions.
Urbanization, especially in developing countries, is clearly associated with increased energy use. As populations become more urbanized and commercial fuels, especially electricity, become easier to obtain, the demand for energy services such as refrigeration, lighting, heating, and cooling increases. The number of people living in urban areas almost doubled between 1970 and 1995, growing from 1.36 billion, or 37% of the total, in 1970 to 2.57 billion, or 45% of the total, in 1995 (UN, 1996).
Driving forces influencing the use of HFCs include both its suitability as a replacement for CFCs and HCFCs, as well as an awareness of the contribution of HFCs to global climate change. It is expected that this awareness will continue to drive decisions to use HFCs only in highest value applications. Some countries have enacted regulations limiting emissions of HFCs while others have established voluntary agreements with industry to reduce HFC use (see Appendix to this chapter).
Global projections of primary energy use for the buildings sector show a doubling, from 103EJ to 208EJ, between 1990 and 2020 in a baseline scenario (WEC, 1995a). The most rapid growth is seen in the commercial buildings sector, which is projected to grow at an average rate of 2.6% per year. Increases in energy use in the EITs are projected to be as great as those in the developing countries, as these countries recover from the economic crises and as the growth in developing countries begins to slow. Under a scenario where state-of-the-art technology is adopted, global primary energy consumption in the buildings sector will only grow to about 170EJ in 2020. A more aggressive ecologically driven/advanced technology scenario, which assumes an international commitment to energy efficiency as well as rapid technological progress and widespread application of policies and programmes to speed the adoption of energy-efficient technologies in all major regions of the world, results in primary energy use of 140EJ in 2020 (WEC, 1995a).
The IPCCs IS92a scenario projected baseline global carbon dioxide emissions from the buildings sector to grow from 1900 MtC to 2700MtC between 1990 and 2020. An analysis of the potential reductions from implementation of energy-efficient technologies found that annual global carbon dioxide emissions from the buildings sector could be reduced by an estimated 950MtC in 2020 compared to the IS92a baseline scenario (Acosta Moreno et al., 1996). Over 60% of these projected savings are realized through improvements in residential equipment and the thermal integrity of buildings globally. Carbon dioxide emissions from commercial buildings grow from 37% to 41% of total buildings emissions between 1990 and 2020 as a result of expected increases in commercial floor space (which implies increases in heating, ventilation, and air conditioning systems (HVAC)) as well as increased use of office and other commercial sector equipment (Acosta Moreno et al., 1996; WEC, 1995a).
The B2 scenario from the IPCCs Special Report on Emissions Scenario projects buildings sector carbon dioxide emissions to grow from 1,790MtC in 1990 to 3,090MtC in 2020. The most rapid growth is seen in the developing countries, which show an average growth in buildings-related carbon dioxide emissions of over 3% per year. In contrast, this scenario envisions that the emissions from buildings in the EIT region continue to decline, at an average annual rate of 1.3% (Nakicenovic et al., 2000).
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