IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change

6.5.1 Recent advances in potential estimations from around the world

Chapter 3 of the TAR (IPCC, 2001) provided an overview of the global GHG emission reduction potential for the residential and commercial sectors, based on the work of IPCC (1996) and Brown et al. (1998). An update of this assessment has been conducted for this report, based on a review of 80 recent studies from 36 countries and 11 country groups, spanning all inhabited continents. While the current appraisal concentrates on new results since the TAR, a few older studies were also revisited if no recent study was located to represent a geopolitical region in order to provide more complete global coverage. Table 6.2 reviews the findings of a selection of major studies on CO2 mitigation potential from various countries around the world that could be characterized in a common framework. Since the studies apply a variety of assumptions and analytical methods, these results should be compared with caution (see the notes for each row, for methodological aspects of such a comparison exercise).

According to Table 6.2, estimates of technical potential range from 18% of baseline CO2 emissions in Pakistan (Asian Development Bank, 1998) where only a limited number of options were considered, to 54% in 2010[8] in a Greek study (Mirasgedis et al., 2004) that covered a very comprehensive range of measures in the residential sector. The estimates of economic potential[9] vary from 12% in EU-15 in 2010[10] (Joosen and Blok, 2001) to 52% in Ecuador in 2030[11] (FEDEMA, 1999). Estimates of market potential[12] range from 14% in Croatia, focusing on four options only (UNFCCC NC1 of Croatia, 2001), to 37% in the USA, where a wide range of policies were appraised (Koomey et al., 2001).

Table 6.2: Carbon dioxide emissions reduction potential for residential commercial sectors

Country/region Reference Type of potential Description of mitigation scenarios Potential Measures with lowest costs Measures with highest potential Notes 
Million tCO2 Baseline (%) 
Case studies providing information for demand-side measures 
EU-15 Joosen and Blok, 2001  Technical 25 options: retrofit (insulation); heating systems; new zero & low energy buildings, lights, office equipment & appliances; solar and geo-thermal heat production; BEMS for electricity, space heating and cooling. 310 21% 1. Efficient TV and peripheries; 2. Efficient refrigerators & freezers; 3. Lighting Best Practice. 1.Retrofit: insulated windows; 2.Retrofit: wall insulation; 3.BEMS for space heating and cooling. [1].4%; [4].Fr-ef.; [5].TY 2010. 
Economic 175 12% 
Canada Jaccard and Associates, 2002 Market Mainly fuel switch in water and space heating, hot water efficiency and the multi-residential retrofit program in households; landfill gas, building shell efficiency actions and fuel switch in commerce. 22 24% n.a. (not listed in the study) 1.Electricity demand reductions; 2.Commercial landfill gas; 3.Furnaces & shell improvements. [1].10%; [5].TY 2010. 
Greece Mirasgedis et al., 2004 Technical 14 technological options: fuel switch, controls, insulation, lights, air conditioning and others. 13 54% 1. Replacement of central boilers; 2. Use of roof ventilators; 3. Replacement of AC. 1.Shell, esp. insulation; 2.Lighting & water heating; 3.Space heating systems. [1].6%; [4].Fr-ef; [5].TY 2010; [7].R only. 
Economic 25% 
UK DEFRA, 2006  Technical 41 options: insulation; low-e double glazing windows; various appliances; heating controls; better IT equipment, more efficient motors, shift to CFLs, BEMS, etc. 46 24% (res. only) 1. Efficient fridge/ freezers; 2. Efficient chest freezers; 3. Effi-cient dishwashers. 1.Efficient gas boilers; 2.Cavity insulation; 3.Loft insulation. [1].7-5%:R/C; [4].BL: Johnston et al., 2005; [5].BY 2005. 
Australia Australian Greenhouse Office, 2005 Market Fridges and other appliances, air conditioners, water heating, swimming pool equipment, chillers, ballasts, standards, greenlight Australia plan, refrigerated cabinets, water dispensers, standby. 18 15% 1.Standby programs; 2.MEPS for appliances 1999; 3.TVs on-mode. 1.Packaged air-conditioners; 2.Ballast program in 2003; 3.Fluorescent bulbs. [1].5%; [4].BL: scenario without measures; [5].BY 2005. 
Estonia Kallaste et al., 1999 Market 4 insulation measures: 3d window glass, new insulation into houses, renovation of roofs, additional attic insulation. 0.4 2.5% of nation. emis. 1. New insulation; 2. Attic insulation; 3. 3d window glass. 1.New insulation; 2.3d window glass; 3.Attic insulation. [1].6%; [5].BY 1995; TY 2025. 
China ERI, 2004 Enhanced market Key policies: energy conservation standards, heat price reform, standards & labelling for appliances, energy efficiency projects, etc. 422 23% n.a. (not listed in the study) n.a. (not listed in the study) [1].N.a. 
New EU Member Statesa) Petersdorff et al., 2005 Technical Building envelope esp. insulation of walls, roofs, cellar/ground floor, windows with lower U-value; and renewal of energy supply. 62 1. Roof insulation; 2. Wall insulation; 3. Floor Insulation. 1. Window replacement; 2. Wall insulation; 3. Roof insulation. [1] 6%; [4] Fr-ef; [5] BY 2006; TY 2015. 
Hungary Szlavik et al., 1999 Technical 25 technological options and measures: building envelope, space heating, hot water supply, ventilation, awareness, lighting, appliances. 22 45% 1. Individual metering of hot water; 2. Water flow controllers; 3. Retrofitted windows. 1. Post insulation; 2. Retrofit of windows; 3. Replacement of windows. [1] 3%; [5] TY 2030.  
Economic 15 31% 
Myanmar Asian Development Bank, 1998 Economic 5 options: shift to CFLs, switch to efficient biomass and LPG cooking stoves, improved kerosene lamps, efficient air conditioners. N.a. 1. Biomass cooking stoves, 2. Kerosene lamps, 3. CFLs. 1. Biomass cooking stoves, 2. LPG cooking stoves, 3. CFLs. [1] 10%. 

Table 6.2b.

Country/region Reference Type of potential Description of mitigation scenarios Potential Measures with lowest costs Measures with highest potential Notes 
Million tCO2 Baseline (%) 
India Reddy and Balachandra, 2006 Market Lighting: mixture of incandescents, fluorescent tubes and CFLs, exchange of traditional kerosene and wood stoves and water heaters for efficient equipment. 17 33% 1. Efficient packages of lighting; 2. Kerosene stoves; 3. Wood stoves. 1. Wood stoves, 2. Efficient packages of lighting; 3. Kerosene stoves. [1] n.a.; [5] TY 2010; [7] R only. 
Republic of Korea Asian Development Bank, 1998 Economic 7 options: heating - condensing gas boilers, solar hot water systems, insulation standards; cooling - air conditioners; improved lights - shift to fluorescents and CFLs; efficient motors and inverters. 20 17% 1. Heating: gas boilers, solar hot water, insulation standards; 2. Air conditioners; 3. Inverters & motors. 1. Improved lights; 2. Motors & inverters; 3. Gas boiler RES, solar hot water system, insulation standards. [1] 8.5%; [5] BY1998.  
Ecuador FEDEMA, 1999 Economic 6 main options: improvements of appliances, lighting systems, electricity end-uses esp. in rural areas and in the services, solar water heating, public lighting. 52% 1. Lights; 2. Electric appliances (esp. rural areas); 3. Electricity end-use in services. 1. Improved electricity end-uses in rural areas; 2. Electric appliances (esp. in rural areas); 3. Light systems. [1] 10%; [5] TY 2030.  
Thailand Asian Development Bank, 1998 Technical 3 technological programs: lighting (shift to fluorescents), refrigerator (insulation and compressors) and air-conditioning. 15 31% 1. Lighting, 2. Efficient refrigerators, 3. Air conditioning. 1. Efficient air-conditioning, 2. Efficient refrigerators, 3 Lighting. [1] 10%; [5] BY 1997; [7] R only. 
Economic 6.1 13% 
Pakistan Asian Development Bank, 1998 Technical Energy efficiency improvements of electric appliances and other end-use devices such as lights, fans, refrigerators, water heaters and improvement of building design. 18% 1. Improved lights, 2. Efficient ceiling fans, 3. More efficient refrigerators. 1. Efficient ceiling fans, 2. Improved lights, 3. Improved building design. [1] 8%; [5] BY 1998.  
Indonesia AIM, 2004 Technical 9 Main technological options: energy efficient appliances such as refrigerator and air conditioners, lights (shift from incandescents to fluorescents), kerosene, electricity and gas water heater, kerosene and gas heater, wall and window insulation and others. 13.5 25% Efficient refrigerator, electricity and gas water heater, kerosene and gas heater, lights, air-conditioners (not ranked). 1. Efficient refrigerators, 2. Fluorescent lamps, 3. Efficient electric water heater (ranking at negative marginal cost). [1] 5%; [2] Integrated Assessment; [4] Fr-ef.; [7] R only. 
   Economic 10.2 19% 
Argentina AIM, 2004 Technical 3.8 22% 
   Economic 3.3 19% 
Brazil AIM, 2004 Technical 5.4 41% 
   Economic 4.8 36% 
Poland Gaj and Sadowski, 1997 Technical 13 options: lights in streets, commerce & households, gas boiler controls, appliances, heat meters, thermal insulation for walls and roofs, window tightening & replacement, fuel switch from coal to gas, solar or biomass, DH boilers. 43 26% 1. Efficient street lighting; 2. Improved controls of small gas boilers; 3. Efficient lighting in commerce. 1. Insulation of walls, 2. Improvement of home appliances, 3. Fuel switching from coal to gas, solar and biomass. [1] n.a.; [4] BL: UNFCCC NC3 of Poland, 2001.  
Economic 30 18% 
Russia Izrael et al., 1999 Technical Downsized thermal generators (boilers and heaters), thermal insulation (improved panels, doors, balconies, windows), heat and hot water meters and controls, hot water distribution devices, electric appliances. 182 47% n.a. (not listed in the study) n.a. (not listed in the study) [1] n.a.; [4] BL: UNFCCC NC3 of Russia, 2002; PNNL & CENEf, 2004; [5] TY 2010. 
Economic 52 13% 

Table 6.2c.

Country/region Reference Type of potential Description of mitigation scenarios Potential Measures with lowest costs Measures with highest potential Notes 
Million tCO2 Baseline (%) 
South Africa De Villiers and Matibe, 2000 De Villiers, 2000 Technical 21 options: light practices; new & retrofits HVAC; stoves, thermal envelope; fuel switch in heaters; standards & labelling; for hot water: improved insulation, heat pumps, efficient use; solar heating. 41 23% 1. Energy star equipment; 2. Lighting retrofit; 3. New lighting systems. 1. Hybrid solar water heaters; 2. New building thermal design; 3. New HVAC systems. [1] 6%; [4] Fr-ef.; [5] BY 2001; TY 2030. 
Economic 37 20% 
Croatia UNFCCC NC1 of Croatia, 2001 Market Electricity savings for not heating purposes (low energy bulbs, more efficient appliances, improved motors), solar energy use increase, thermal insulation improvement. 14% 1. Bulbs & appliances; 2. Solar energy use increase; 3. Insulation improvement 1. Insulation improvement; 2. Solar energy use increase; 3. Bulbs & appliances. [1] n.a. 
Studies providing information about both supply and demand-side options not separating them 
New EU Member Statesa) Lechtenboh-mer et al., 2005 Economic Improvement in space and water heating, appliances and lighting, cooling/freezing, air-conditioning, cooking, motors, process heat, renewable energies, reduced emissions from electricity generation. 81 37% n.a. (not listed in the study) R: 1.Insulation; 2.Heating systems, fuel switch, DH&CHP; C: 1. Energy efficiency, 2. Renewables. [1] 3-5%; [5] BY 2005; [7] C includes agriculture. 
USA Koomey et al., 2001 Market Voluntary labelling, deployment programmes, building codes, new efficiency standards, government procurement, implementation of tax credits, expansion of cost-shared federal R&D expenditures. 898 37% n.a. (The study did not examine a GHG potential supply cost curve). 1. Lighting; 2. Space cooling; 3.Space heating.  [1] 7%; [5] BY 1997. 
Japan Murakami et al., 2006 Technical 15 options: new and retrofit insulation, double glazing window, home appliances (water & space heating/cooling, lighting, cooking), PVs, solar heating, shift to energy efficient living style, low-carbon electricity generation. 46 28% n.a. (not listed in the study) 1. Water heater; 2. Space heater; 3. Home appliances.  [1] n.a.; [7] R only. 
Germany Martinsen et al., 2002 Technical Two options: fuel switch from coal and oil to natural gas and biomass and heat insulation. 31 26% n.a. (not listed in the study) 1.Heat insulation; 2.Fuel switch from coal & oil to gas & biomass.  [1] n.a.; [5] BY 2002; [7] R only. 

Notes specify those parameters which are different from those identified below (the number of a note is the number of the model parameter):

a) Hungary, Slovakia, Slovenia, Estonia, Latvia, Lithuania, Poland and the Czech Republic

1. Discount Rate (DR) belongs to the interval [3%; 10%]. 2. Most models are Bottom-up (BU). 3. All models consider CO2. If a study considered GHGs, CO2 only was analysed, if the study assessed C, potential was converted into CO2. 4. Baseline (BL) is Business-as-Usual Scenario (BAU) or similar (Frozen efficiency scenario is abbreviated as fr-ef). 5. Base year (BY) is 2000; Target year (TY) is 2020. 6. Costs covered: cost of incremental reduction, abatement costs, costs of avoided or saved or mitigated CO2, marginal costs. 7. Estimations are made for Residential (R) and commercial (C) sectors in sum.

Our calculations based on the results of the reviewed studies (see Box 6.1) suggest that, globally, approximately 29% of the projected baseline emissions by 2020[13] can be avoided cost-effectively through mitigation measures in the residential and commercial sectors (high agreement, much evidence). Additionally at least 3% of baseline emissions can be avoided at costs up to 20 US$/tCO2 and 4% more if costs up to 100 US$/tCO2 are considered. Although due to the large opportunities at low-costs, the high-cost potential has been assessed to a limited extent and thus this figure is an underestimate (high agreement, much evidence). These estimates represent a reduction of approximately 3.2, 3.6 and 4.0 billion tonnes of CO2-eq in 2020, at zero, 20 US$/tCO2 and 100 US$/tCO2, respectively. Due to the limited number of demand-side end-use efficiency options considered by the studies, the omission of non-technological options, the often significant co-benefits, as well as the exclusion of advanced integrated highly efficiency buildings, the real potential is likely to be higher (high agreement, low evidence). While occupant behaviour, culture and consumer choice as well as use of technologies are also major determinants of energy consumption in buildings and play a fundamental role in determining CO2 emissions, the potential reduction through non-technological options is not assessed. These figures are very similar to those reported in the TAR for 2020, indicating the dynamics of GHG reduction opportunities. As previous estimates of additional energy efficiency and GHG reduction potential begin to be captured in a new baseline, they tend to be replaced by the identification of new energy-efficiency and GHG-mitigation options. For comparison with other sectors these potentials have been extrapolated to 2030. The robustness of these figures is significantly lower than those for 2020 due to the lack of research for this year. The extrapolation of the potentials to the year 2030 suggests that, globally, at least 31% of the projected baseline emissions can be mitigated cost-effectively by 2030 in the buildings sector. Additionally at least 4% of baseline emissions can be avoided at costs up to 20 US$/tCO2 and 5% more at costs up to 100 US$/tCO2 (medium agreement, low evidence)[14]. This mitigation potential would result in a reduction of approximately 4.5, 5.0 and 5.6 billion tonnes of CO2-eq at zero, 20 US$/tCO2 and 100 US$/tCO2, respectively, in 2030. Both for 2020 and 2030, low-cost potentials are highest in the building sector from all sectors assessed in this report (see Table 11.3). The outlook to the long-term future assuming options in the building sector with a cost up to 25 US$/tCO2 identifies the potential of approximately 7.7 billion tonnes of CO2 in 2050 (IEA, 2006d).

Box 6.1: Methodology for the global assessment of potentials and costs of CO2 mitigation in buildings

This chapter evaluated the potential for GHG mitigation in buildings and associated costs based on the review of existing national and regional potential estimates. For this purpose, over 80 studies containing bottom-up mitigation potential estimates for buildings were identified from 36 countries and 11 country groups covering all inhabited continents. One study (AIM, 2004) covered the entire planet, but it was not suitable for the purposes of this report, as it assessed a very limited number of mitigation options.

To allow the comparison of studies in a common framework, their main results and related assumptions were processed and inserted into a database containing the key characteristics of the methods used and results. To eliminate the major effects of different methodological assumptions, only those studies were selected for further analysis whose assumptions fell into a range of common criteria. For instance, studies were only used for further assessment if their discount rates fell in the interval of 3–10%. For studies which did not report their baseline projections, these were taken from the latest available National Communications to the UNFCCC, or other recent related reports.

Table 6.2 presents the results of a selection of major mitigation studies meeting such criteria for different parts of the world. For definitions of various mitigation potentials see Chapter 2, Section

The next step was to aggregate the results into global and regional potential estimates, as a function of CO2 costs. Only three studies covered a 2030 target year and they were for countries with insignificant global emissions, thus this was only possible for 2020 in the first iteration. Since few studies reported potentials as a function of cost (typically only technical/economic or market potentials were reported), only 17 studies from the remaining subset meeting our other selection criteria could be used. IPCC SRES or WEO scenarios could not be used as a baseline because little information is available for these on the technology assumptions in buildings. In order to make sure the potentials are entirely consistent with the baseline, an average baseline was created from the studies used for the global potential estimates. For the global potential estimates and the baseline construction, the world was split into seven regions[16]. For each such region, two to four studies were located, thus dividing each region into two to four sub-regions represented by these marker countries in terms of emission growth rates and potential as a percentage of baseline. CO2 baseline emissions in the seven regions were estimated starting with 2000 IPCC A1B and B2 (SRES) data and applying the CO2 growth rates calculated for each region as the population weighted average CO2 baseline growth rates of two to four sub-regions. The baseline projections were estimated for 2000–2020 based on mainly 2020 data from the studies; these trends were prolonged for the period 2020–2030. Since three of the seventeen studies used a frozen efficiency baseline, the baseline used in this chapter can be considered a business-as-usual one with some frozen efficiency elements. The resulting baseline is higher than the B2 (SRES) scenario but lower than A1B (SRES) and WEO scenarios.

Analogously, CO2 potentials as a percentage of the baseline in cost categories (US$/tCO2: (<0); (0;20); (20;100)) were calculated based on population weighted average potentials in the sub-regions for each cost category .While the three studies using a frozen efficiency baseline result in a relatively higher potential than in studies using a BAU baseline, this does not compromise the validity of the global potential, since for the regions applying a frozen efficiency baseline, the latter baseline was used in calculating the global total. The results of these estimates are presented in Table 6.3.

As mentioned above, only three studies covered the baseline or mitigation potential for 2030. Therefore these figures were derived by extrapolating the 2020 figures to 2030. Since the simple exponential formula used for such extrapolations by other sectors was found to yield disputably high or low results in some cases, a modified exponential function was used which allows regulating the maximum potential considered theoretically achievable for different regions[17]. The results of the projections are presented in Table 6.4

The literature on future non-CO2 emissions and potentials for their mitigation have been recently reviewed in the IPCC/TEAP report (2005). The report identifies that there are opportunities to reduce direct emissions significantly through the global application of best practices and recovery methods, with a reduction potential of about 665 million tonnes of CO2-eq of direct emissions in 2015, as compared to the BAU scenario. About 40% of this potential is attributed to HFC emission reduction covered by the Kyoto Protocol to the UNFCCC, while HCFCs and CFCs regulated by the Montreal Protocol contribute about 60% of the potential. A key factor determining whether this potential will be realized is the costs associated with the implementation of the measures to achieve the emission reduction. These vary considerably from a net benefit to 300 US$/tCO2-eq. Refrigeration applications and stationary and mobile air conditioning contribute most to global direct GHG emissions. Action in these sub-sectors could therefore have a substantial influence on future emissions of HCFCs and HFCs. The available literature does not contain reliable estimates for non-CO2 mitigation potentials in the long-term future, including the year 2030. Therefore, the 2015 figures can serve as low estimates of the potentials in 2030, taking into account that upcoming progressive policies in many countries have already led to new products with very low non-CO2 emissions as compared to their previous analogues.

  1. ^  Australia, Denmark, Finland, France, Germany, Italy, Japan, Norway, Sweden, the United Kingdom, and the United States.
  2. ^  If the approx. formula of Potential 2020 = 1 - ( 1 - Potential 2010)20/10 is used to extrapolate the potential as percentage of the baseline into the future (2000 is assumed as a start year), this corresponds to approx. 78% CO2 savings in 2020.
  3. ^  In this chapter we refer to ‘cost-effective’ or ‘economic’ potential, to remain consistent with the energy-efficiency literature, considering a zero-carbon price.
  4. ^  Corresponds to an approx. 22% potential in 2020 if the extrapolation formula is used.
  5. ^  Corresponds to an approx. 38% potential in 2020 if the formula is applied to derive the intermediate potential.
  6. ^  For definitions of technical, economic, market and enhanced market potential, see Chapter 2 Section
  7. ^  The baseline CO2 emission projections were calculated on the basis of the reviewed studies, and are a composite of business-as-usual and frozen efficiency baseline.