How can we estimate carbon emissions and reduction of buildings at the local government level in South Korea?

Study site and conditions

Jeollanam-do is located in the southwestern part of the Korean Peninsula (34.8679° N, 126.9910° E), comprising mountainous and plain regions (inland) and island regions (coastal), as shown in Fig. 1. Its total population is 1.8 million, and its climate is characterized as humid temperate. Jeollanam-do has more than 50% of buildings older than 30 years, of which household buildings account for over 80%. Among household buildings, single houses are mainly located in old towns in urban/suburban areas while apartment buildings are in urban areas. Buildings for business and public buildings are mainly located in urbanized areas in cities. Each year, about 115,000 buildings are newly constructed and about 70,000 buildings are remodeled. The total number of certified GBs is 205, with the number increasing every year. As of 2022, the number of ZEB is 122. The ZEB buildings are for public use (such as institutes, kinder gardens, government offices, community centers, public health centers and etc.) and located in urban areas. With the rise of retrofitting of public buildings, this number is increasing every year. The final energy consumption of Jeollanam-do was the highest in the country in 2020; cities within Jeollanam-do with high GHG emissions include Yeosu, Suncheon, and Mokpo, which show high electricity and city gas consumption.

Fig. 1

Study site (Jeollanam-do, South Korea) including 5 cities (-sis) and 17 counties (-guns). Note: retrieved from www.jeonnam.go.kr and edited by authors.

Projecting buildings’ gross floor area

Estimation of GHG emissions from the building sector in Jeollanam-do from 2022 to 2050 was carried out by estimating the buildings’ gross floor area (GFA) and then estimating emissions according to the GFA (Fig. 2). The premise of this analysis is that there is a positive correlation between the buildings’ GFA and GHG emissions (Welegedara et al., 2021). Estimation of the GFA of all buildings, including demographic prospects, was first conducted, followed by estimation by building use (household, business, and public use). The reason for the latter estimation is that GBs targets are mainly classified into household, business, and public use (2050 Carbon Neutrality Commission, 2021a; 2021b), while the former estimation is for ease of including the demographic prospects.

Fig. 2

Research flow chart. GHG: greenhouse gas; GFA: ground floor area.

Estimation of the GFA of all buildings from 2022 to 2050 was made through a linear regression of the GFA of the buildings in Jeollanam-do for the past 10 years (MOLIT, 2012–2021), calculating the estimated values using the regression equation for the concerned period (Fig. 2). The GFA of all buildings in Jeollanam-do was extracted from the national statistics on the total floor area of buildings by province. For demographic prospects, the total population growth rate (-3.1%) of the population projections of Jeollanam-do for the period of 2015–2045, prepared by Statistics Korea (2017), was divided by the number of years between 2022 and 2050. The total estimated GFA by year was then classified as under 10 years old and over 10 years old. This was done because buildings under 10 years old are subject to ZEB standards (Perlova et al., 2015; Saman, 2013; Stefanović et al., 2014), while over-10-year-old-buildings are subject to retrofitting (Arikan et al., 2005; McArthur and Jofeh, 2015).

Estimation of the GFA by building use was based on the estimated GFA data of all buildings. The trend of GFA increase/decrease over the past 10 years was modeled. The building sector was classified according to household, business, or public use. Household use includes detached houses and apartments; business use includes neighborhood living, sales, transportation, lodging, and recreational facilities; public use consists of education and research, business, elderly, cultural assembly, religious, and medical facilities. Buildings for industrial, agricultural, and fishery uses are excluded from this study, because they do not belong to the building sector in carbon-neutral scenarios: industrial buildings belong to the industrial sector, and buildings for agriculture and fisheries belong to the agriculture and fisheries sector.

Projecting GHG emissions at the building level

The GFA of each building use is estimated by year, and estimated annual GHG emissions increase as the GFA increases. In order to calculate GHG emissions corresponding to the GFA, this study utilized data from the Korea Real Estate Board for the period of 2018–2021, which provides energy consumption per GFA (unit: TOE, the ton of oil equivalent). Data on energy consumption by building use in Jeollanam-do from 2018 to 2021, were obtained from Green Together, which has been providing a web-based information service on energy consumption by building use across the country since 2018. The estimated emissions were classified into household, business, and public use, similar to the estimated GFA. Although the Green Together data is highly useful because it provides the energy consumption according to the GFA of ides the energy it is limited to 4-year data. Therefore, this dataset was compared with the statistical data on 10-year building use (2012–2021) presented in the Yearbook of Energy Statistics by region. Between 2018 and 2021, the values provided by Green Together were confirmed to be similar to those from the Yearbook of Energy Statistics, justifying the use of Green Together data for this study. The energy consumption from 2022 to 2050 was estimated by applying the linear regression model to the GFAs for household, business, and public building use. Finally, the estimated building energy consumption was converted into GHG emission estimates, following the formula from the Guidelines for Local Government Greenhouse Gas Inventories (Korea Environment Corporation, 2016). In order to increase the accuracy of GHG emission estimates, the emission factor in the calculation formula was applied differently for household, business, or public use, as well as for different energy sources such as electricity, city gas, and district heating.

Calculation of CO₂ mitigation at the building level

Carbon neutrality by 2050 is impossible according to the calculated emissions; therefore, a GHG emissions reduction target was required. Korea’s national target in the building sector for GHG emissions reduction is to reduce emissions by 88.4% of the 2018 level by 2050 (2050 Carbon Neutrality Commission, 2021b), and by 40% of the 2018 level by 2030 (2050 Carbon neutrality commission, 2021a). This study calculated GHG emission reduction in Jeollanam-do by 2030 and 2050, according to the above-noted reduction targets. In addition, by applying the back-casting approach (Ministry of Environment, 2021), the reduction targets were initially set, and then scenarios were used to establish paths to achieve them. Two scenarios were set, and both aimed to realize an 88.4% reduction in emissions compared to 2018 by 2050 corresponding to the carbon neutrality target through the path following the P1 scenario of the IPCC Special Report on the impacts of global warming of 1.5 °P (IPCC, 2018) (Fig. 3). Emission reduction is to be realized through the transition to ZEB for the GFA of under 10 year-old-buildings, and through retrofitting for the GFA of over 10 year-old-buildings. In Scenario 1, the conversion rate for ZEBs and retrofitting increases with a linear slope from 2023 to 2050, reducing GHG emissions. In Scenario 2, the period from 2023 to 2027 is set to as a preparatory period for institutional and business foundation for the actual conversion through two reduction means from 2028, followed by a steep decrease in GHG emissions until 2035, and then a gradual decrease in GHG emissions from 2036 until 2050.

Fig. 3

P1 scenario for global net-zero (IPCC, 2018).

Projection of total GFA and the GFA by building use

The total GFA, taking geographic projections into account, is estimated to increase to 177 million m² in 2021, 180 million m² in 2023, 198 million m² in 2027, 212 million m² in 2030, and 300 million m² in 2050 (Fig. 4). This means that in 29 years from 2021, the total GFA will increase by 1.69 times. For the period of the 2nd action plan Jeollanam-do GBs (2023–2027), the total GFA is expected to increase by 18 million m², with an annual increase of 4.5 million m².

Fig. 4

Total projected GFA (2012 – 2050) and total observed GFA (2012 – 2021). GFA: ground floor area.

The GFA of household buildings is expected to increase from 88 million m² to 95 million m² in the period of 2023–2027 (the period for the 2nd action plan Jeollanam-do GBs), to 99 million m² by 2030 (the target year for 2030 NDC of the Republic of Korea), and to 129 million m² by 2050 (the target year for 2050 carbon neutrality scenarios), as shown in Fig. 5. Of the total GFA of household buildings, buildings under 10-year-old accounted for 23–31%, and buildings over 10-year-old accounted for 69–77%. The GFA of business buildings is projected to increase from 41 million m² to 45 million m² in the period of 2023–2027, to 48 million m² in 2030, and to 65 million m² in 2050. The proportion of under 10 year-old-buildings was slightly higher than that of household buildings, up to 36%, and the proportion of over 10 year-old-buildings was up to 70%. The GFA of public buildings is expected to increase from 19 million m² to 21 million m² in the period of 2023–2027, to 22 million m² in 2030, and to 28 million m² in 2050. The continually increasing trend of GFA of Jeollanam-do, regardless of the decreasing trend of the population, is because the −3% reduction in the total population was applied to the increase in total GFA divided by year. In terms of GFA projections by building sector in Jeollanam-do, household buildings showed the steepest increase, while business and public buildings showed a very modest increase (Fig. 5). Dividing the GFA by years of usage, household and business buildings accounted for about 30% of under 10-year-old-buildings while about 70% were over 10 year-old-buildings. For public buildings, those over 10-year-old were estimated to account for about 90%. This suggests the importance of buildings that are over 10-year-old in the effort to increase the effectiveness of GB policies.

Fig. 5

Projected GFA and GHG emissions by building use (2018 – 2050). GHG: greenhouse gas; HBE: household building emissions; BBE: business building emissions; PBE: public building emissions; over 10 yrs: over 10 year-old-buildings; under 10 yrs: under 10 year-old-buildings.

GHG emission projection in buildings

GHG emissions based on the GPA were projected to be 3.7 to 3.9 million TOE in 2023–2027, 4.0 million TOE in 2030, and 5.0 million TOE in 2050 (Fig. 5). This is an increase of 0.1–0.3 million TOE in 2030 from 2023, and an increase of 1.1–1.3 million TOE in 2050 from 2023. Household building emissions are projected to be 1.8 million TOE in 2018, 2.0 to 2.2 million TOE in 2023–2027, 2.3 million TOE in 2030, and 3.2 million TOE in 2050. GHG emissions from business use are estimated to be 1.1 million TOE in 2018, 1.11 million TOE in 2023–2027, 1.12 million TOE in 2030, and 1.14 million TOE in 2050. Public building emissions are expected to be 0.58 million TOE in 2018, 0.58 to 0.59 million TOE in 2023–2027, 0.59 million TOE in 2030, and 0.61 million TOE in 2050. That is, out of the total building emissions, 52% to 62% would be from household buildings, 23% to 31% from business buildings, and 12% to 16% from public buildings. Emissions from household and business buildings account for 83% to 85% of the total. Reflecting the trend of the estimated GFA by building use, household buildings show a remarkable increase until 2050, while business and public buildings show a very slow increase. In addition, GHG emissions of under 10 year-old-buildings account for 30% while over 10 year-old-buildings account for 70%, showing a direct proportional relationship to the ratio of the calculated GFA by the year of use.

Towards 2050, the proportion of household and business buildings of under-10-year-old and over-10-year-old is relatively fixed, but the quantity of over 10 year-old public buildings is expected to decrease towards 2050. Accordingly, public building emissions are also expected to decrease.

GHG reduction projection in buildings by scenarios

The proposal to raise the 2030 National GHG Reduction Target (2050 Carbon Neutrality Commission, 2021a) aims to have a 40% reduction in 2018 emissions by 2030, and the 2050 Carbon Neutral Scenario (2050 Carbon Neutrality Commission, 2021b) proposes an 88.1% reduction in 2018 emissions by 2050. By applying the national policy goal as the target for the building sector in Jeollanam-do, the GHG reduction target was calculated as 2.4 million TOE by 2030 (1.2 million TOE reduction) and 0.4 million TOE by 2050 (3.2 million TOE reduction) in 2050. This means that the building sector in Jeollanam-do aims to reduce GHG emissions from 3.6 million TOE in 2018 to 0.1 million TOE in 2030, and to 0.7 million TOE in 2050.

GHG reduction goal and its pathways by scenarios

The GHG reduction targets for the building sector were calculated as 1.4 million TOE for household buildings, 0.7 million TOE for business buildings, and 0.35 TOE for public buildings by 2030 (Fig. 6). The pathways in Scenarios 1 and 2 show emissions increase at the same rate from 2018 to 2022, and then follow different trends from 2023 onwards. Scenario 1 shows a straight line path with a negative slope from 2023, and Scenario 2 shows an increase in emissions after 2023, then the trend breaks and starts to decrease from 2028, showing a sharp decline until 2035, then a very modest decline until 2050 (Fig. 6).

Fig. 6

GHG emissions by GHG reduction scenarios (2018 – 2050) by building use. GHG: greenhouse gas, HBE: household building emissions, BBE: business building emissions, PBE: public building emissions.

In Scenario 1, it appears that the reduction targets can be achieved with no problem as long as the annually set reduction is faithfully performed. If the practical means of GB construction-the application of ZEB construction to under 10 year-old-buildings and retrofitting to over 10 year-old-buildings-are continuously applied, it is expected that the GHG reduction target in the building sector can be achieved. Meanwhile, timing is a challenge in implementation, as the institutional and technological foundations should be well established to reduce GHG emissions from 2023 according to the presented path. However, applying ZEB construction to under 10 year-old-buildings present feasibility issues. In Jeollanam-do, ordinances by city and county have not yet been completed, and the overall technical competency is inadequate for ZEB. Therefore, it is questionable whether ZEB will induce any GHG reduction effect from 2023. Retrofitting for over-10-year-old buildings may create a greater GHG reduction effect than zero-energy construction, because the retrofitting projects for public buildings in Jeollanam-do have been actively carried out. However, retrofitting for old private buildings, which make up most of the old buildings, is still scarce. Therefore, considering the realistic aspects, the possibility of achieving the GHG reduction targets through this scenario appears to be low.

Scenario 2 is characterized by maintaining the current level of emission growth until 2027, then a sharp drop in emissions follows from 2028. The most important period for GHG reduction is 2028–2035. ZEB construction and retrofitting-the practical means of GB construction-must be done at a large scale during this period, particularly for household buildings. In order to secure a large-scale quantity of GBs, it is necessary to secure compulsory quality through legal systems. Through municipal ordinances and guidelines, new houses must be made into ZEBs, and a legal foundation must be created to improve energy efficiency for old houses. In parallel, support measures must be devised and sufficient manpower dedicated to support must be secured in order to induce smooth implementation. If sufficient time and effort are spent to secure the foundation for and raise awareness of the green constriction policy, through pilot projects, voluntary GB construction in the private sector is anticipated. If the basis for accelerating policy implementation is established and needed capacity is built up over the next five years, the reduction path in Scenario 2 will increase the possibility of achieving the targets.