Decomposition and Decoupling Analysis of Life-Cycle Carbon Emission in China ’ s Building Sector

With accelerating urbanization, building sector has been becoming more important source of China’s total carbon emission. In this paper, we try to calculate the life-cycle carbon emission, analyze influencing factors of carbon emission, and assess the delinking index of carbon emission in China’s building sector. The results show: (i) Total carbon emission in China’s building industry increase from 984.69 million tons of CO2 in 2005 to 3753.98 million tons of CO2 in 2013. The average annual growth rate is 18.21% per year. Indirect carbon emission from building material consumption accounted to 96–99% of total carbon emission. (ii) The indirect emission intensity effect was leading contributor to change of carbon emission. The following was economic output effects, which always contributed to increase in carbon emission. Energy intensity effect and energy structure effect took negligible role to offset carbon emission. (iii) Delinking index show the status between carbon emission and economic output in China’s building industry during 2005–2006 and 2007–2008 was weak decoupling; during 2006–2007 and during 2008–2010 was expansive decoupling; and during 2010–2013 was expansive negative decoupling.


Introduction
According to National Economical Industry Classification (GB/T4754-2012) [1], the building industry includes: construction of buildings, civil engineering, renovation and decoration four categories.The energy consumption of building industry includes the energy consumed during occupancy in the various buildings.The sources of carbon emissions are distinguished as two scopes: (i) direct emissions, which refer to the CO 2 emissions from the consumption of energy of building industry; and (ii) indirect emissions, which refer to CO 2 emissions from the consumption of construction materials.Buildings accounted for 32% of total global final energy use (equal to 117 ExaJoules), 19% of energy-related GHG emissions, 51% of global electricity consumption, 33% of black carbon emissions, and an eighth to a third of F-gases emission (large differences in F-gases data are due to differing accounting conventions) [2][3][4].In particular, the building energy consumption in China recently surpassed the US building consumption, and it is expected to increase significantly in the next decades, pushed by the demand for new residential buildings [5][6][7][8].In 2009, the building sector was responsible for one fifth of China's total primary energy consumption and 18% of the overall Chinese GHG emissions.
China has experienced urbanization with an excessively large number of building projects in the past decades [9,10].Even more, China's urbanization is projected to be accelerating in the future [11][12][13].
The accelerating urbanization will lead to a rapid growth of energy usage and material consumption, and a commensurate increase in carbon emission, which means carbon emission from building industry will become more important source of China's total carbon emission.Thus, curbing China's building sector carbon emission, and even China's total carbon emission, requires a better understanding of carbon emission from China's building industry.
Growth in building energy use poses a challenge for the Chinese government; in recent years, to curb energy consumption in buildings, the Chinese government has undertaken many actions at national level, as shown in Table 1.Other countries also face this problem and issue building codes and regulations for energy efficiency [8,[14][15][16][17], as presented in Table 2.
In this paper, we try to calculate carbon emission in China's building industry, to explore its influencing factors, and to assess its decoupling status.To be more specific, we firstly estimate direct (fossil fuel combustion) and indirect (building material consumption) carbon emission in building industry, using China's official data and carbon emission coefficient from IPPCC.Then, we conduct a quantitative analysis of the key influencing factors of carbon emission in China's building industry, using the combination method of kaya identity and logarithmic mean Divisia index (LMDI) model.Finally, we assess the decoupling status between economic output and carbon emission in China's building industry, using Tapio method and decoupling effort index.Given that many developing countries have experienced, or will experience urbanization, which lead to building industry booming, and a commensurate rapidly increase in carbon emission [12,35], our work would bring some implications for carbon emission of building industry in some other developing countries.

Interim Measures for the administration of financial subsidies for renewable energy efficient building materials
To support the Wenchuan earthquake construction waste treatment and recycling, national finance will arrange special funds to support the production of energy-saving building materials and recycling utilization.

December 2010
"National Green Building Innovation Award" and "National Green Building Innovation Award" To do a good job in the management and evaluation of the National Green Building Innovation Award, and guide the healthy development of green building in China.

Italy and Europe
The building energy codes in the U.S. become more stringent Provide an overview on EPBD implementation in Europe and a Geocluster Italian distribution of BERCs in order to show their geographical distribution and their influence on the construction sector practices, focusing in particular on the region of Lombardy, describe the methodology followed for the definition of BERCs in nine municipalities in the same region and present the practical application of one of the nine BERCs to a NZEB residential case study as an example of what the EBPD recast define as NZEB.

Method for Calculating CO 2 Emission
According to National Economical Industry Classification (GB/T4754-2012), the building industry includes: construction of buildings, civil engineering, and renovation and decoration four categories.Based on the previous studies [29,[37][38][39][40][41] and the IPCC method of carbon emission inventories [2], we build the CO 2 emission calculation model for China's building industry.The CO 2 emission calculation of building industry includes two parts: first part is the direct CO 2 emissions and second part is indirect CO 2 emissions shown in the following equation: where C represents total carbon emissions in China's building industry; C dir represents the direct CO 2 emissions, which refer to the CO 2 emissions from the consumption energy of building industry; and C ind represents indirect CO 2 emissions, which refer to CO 2 emissions from the consumption construction materials.
where E i is the i-th energy consumption, and F i (kgCO 2 /kg or kgCO 2 /m 3 or kgCO 2 /kWh) indicates the total energy consumption and the total CO 2 emission coefficient of i-th energy, which is shown in Tables 3 and 4.
where M j is the quantity of j-th kind of consumption construction materials, and β j represents the CO 2 emission coefficient of j-th kind of consumption construction materials, which is shown in Table 5 [42].

Logarithmic Mean Divisia Index Technique
IDA is an analytical tool originated from energy studies.Based on IDA, many specific decomposition methods can be developed and the LMDI approach introduced by Ang and Choi [43] has become the most popular IDA (Index Decomposition Analysis) methodology in the last decade among researchers [44].The reasons are clear: its theoretical and practical advantages (demonstrated by Ang et al. [45]) make it superior to other alternatives.LMDI is an exhaustive (or refined) decomposition method, which ensures decompositions with identically null residual terms.The LMDI can be expressed as an extended Kaya identity, which was first proposed by Kaya [46].Assume that V is an aggregate composed of n factors (x1, . . ., xn), i.e., V = ∑ i V i and V i = x 1,i x 2,i • • • x n,i Further assume that from period 0 to T the aggregate changes from V 0 to V T .The objective is to derive the contributions of the n factors to the change in the aggregate which can be expressed as [47]: Additive form General Formulae of LMDI )) where L(a, b) = (a − b)/(ln a − ln b) is the logarithmic mean of a and b, and L(a, b) = a Because Additive form is easy to understand and calculate, this article uses this form.The extended Kaya identity and LMDI is combined shown in the following formula: (8)     Sustainability 2017, 9, 793 7 of 18 In this expression, we define the following variables, where C t represents the carbon emissions in the t year, the subscript i represents energy type; the superscript t represents year; C it is the carbon emissions from the i-th energy in the t year; E it is the consumption of the i-th energy in the t year; E t is total energy consumption in the t year; Q t is the economical outputs of building industry; F it = C it E it denotes the carbon coefficient of i-th energy; S it = E it E t illustrates the energy structure effect of i-th energy; I t = E t Q t represents energy intensity; and is the effects of intensity of indirect carbon emission.
According to the LMDI method, the change of carbon consumption between a base year 0 and a target year t, is denoted by ∆C, and we use the additive decomposition to make further decomposition of Equation ( 8) to get the following formula: In this expression, we can consider the F it is basically unchanged, so ∆C Ft is 0. Thus, ∆C can be decomposed into the following determinant factors: (10) where ∆C refers to the total changes in carbon emissions, which can be further decomposed into the following indictors: ∆C St (the effect of energy structure: changes in the amount of CO 2 emissions caused by changes in the proportion of nine energy consumption in total energy consumption), ∆C It (the effect of energy intensity: changes in the amount of CO 2 emissions caused by changes in the proportion of total energy consumption in the gross industrial output value), ∆C Qt (the effect of industrial scale: changes in the amount of CO 2 emissions caused by changes in gross output value of construction industry;), and ∆C Pt (the effect of indirect carbon emission intensity: changes in the amount of CO 2 emissions caused by the changes in the proportion of indirect carbon emissions and gross industrial output value).Equations ( 11)-( 17) are used to calculate the changes in the amount of CO 2 emissions caused by the change of the factors of decomposition; based on the LMDI method, ∆C St , ∆C It , ∆C Qt , ∆C Pt can be expressed as follows: ∆C Pt = w ind ln P t P o ( 14)

Decoupling Elasticity Model
The decoupling model is proposed by the Tapio model, which has been developed the OECD decoupling model, which has been widely used to analyze the relationship between economic growth and carbon emission [48,49].In this paper, based on the additive decomposition results of CO 2 emission changes [50], the decoupling elasticity e can be formulated as follows: In this expression, e is the decoupling elasticity, %C is the percent change in carbon emissions, and %GDP is the percent change of economic output of building industry.Carbon emission is the carbon emission of construction for the current year, ∆carbon is the variation of carbon emission at the current time compared with the base period, GDP is the economic output of building industry in the current year, and ∆GDP is the variation of economic output of building industry at the current time compared with the base period.According to the values of e, there are eight logical possibilities [51,52], including weak decoupling, expansive decoupling, expansive negative decoupling, strong negative decoupling, weak negative decoupling, recessive coupling, recessive decoupling, and strong decoupling.

Decoupling Effort Index
In this paper, we identify the factors contributing to carbon emission of building industry in China using the Kaya identity and LMDI techniques; however, they cannot specifically and objectively measure the actual effects of energy conservation and pollution reduction efforts on CO 2 emissions.Effort is a general term referring to the actions that decrease the carbon emissions, both directly and indirectly, such as reducing energy intensity, improving energy efficiency, as well as optimizing the energy structure and excluding the expansion of economical outputs [53].Thus, the effort in absolute terms or absolute effort during the period starting from the base year 0 to year t can be represented as the sum of the three factors identified [54]: The decoupling effect index D from a base year 0 to a target year t takes the following values and is evaluated according to the standards below [54]: D t ≤ 0, denotes no decoupling effort, carbon emissions increase faster than economic outputs because of inefficient emission reduction efforts [55].0 < D t < 1 denotes weak decoupling effort, the efforts of carbon emission reduction have only compensated for a small part of the carbon emissions from economic outputs growth.D t ≥ 1 denotes strong decoupling effort, the emission reduction achieved through various efforts was three or two times higher than the carbon emission increase.

Data Sources and Definition
The data of economic output and energy consumption in China's building industry are from China Energy Statistical Yearbook for the different sectors [56][57][58].The unit of economic output is RMB (Yuan) at constant price of 2005.The unit of energy consumption is ton of coal equivalent (tce).The data of consumption of building materials and building industry output data are from China Statistical Yearbook on Construction [59][60][61].The default value of carbon content, carbon oxidation rate, average lower heating value, and carbon coefficient for different kinds of energy are shown in Tables 3 and 4, based on the GHG Protocol Tool for Energy Consumption in China [62].It should be noted that the carbon coefficients of power sector vary due to the china's energy structure for power generation varying every year.The default value of the ratio of thermal power (%), the ratio of other (water, nuclear, and wind) (%), consumption standard of power and carbon coefficient is represented in Table 4 [17,63].Carbon emission coefficients of building materials are shown in Table 5, according to the reference [64,65].

Estimation of CO 2 Emissions from China's Building Industry
Based on previous studies [17,29,[37][38][39][40], carbon emissions from the building industry should include two parts: one is direct carbon emission from direct fossil fuel combustion in building industry and the other is indirect carbon from building material consumption.

Estimated Direct Carbon Emission
Using Equation ( 2) and carbon emission coefficients shown in Tables 3 and 4, we computed the direct carbon emission of China's building industry (see Figure 1). in Table 4 [17,63].Carbon emission coefficients of building materials are shown in Table 5, according to the reference [64,65].

Estimation of CO2 Emissions from China's Building Industry
Based on previous studies [17,29,[37][38][39][40], carbon emissions from the building industry should include two parts: one is direct carbon emission from direct fossil fuel combustion in building industry and the other is indirect carbon from building material consumption.

Estimated Direct Carbon Emission
Using Equation ( 2) and carbon emission coefficients shown in Tables 3 and 4, we computed the direct carbon emission of China's building industry (see Figure 1).Total direct carbon emission of China's building industry increased from 32.06 million tons of CO2 in 2005 to 50.12 million tons of CO2 in 2013.The compound annual growth rate of direct carbon emission in China's industry was 5.74% during 2005-2013.
As shown in Figure 1, the direct carbon emission includes carbon emission from eight type of fuels (coal, coke, crude oil, fuel oil, gasoline, kerosene, diesel oil and natural gas) and electricity of building industry.The main sources of direct carbon emission in China's building industry are diesel oil coal, gasoline, and electricity.In 2005, burning diesel oil, coal, gasoline, and electricity consumption contributions to total direct carbon emission in China's building industry were 37.34%, 37.29%, 15.70% and 5.62%, respectively.In 2013, burning diesel oil, coal, gasoline, electricity consumption contributions to total direct carbon emission in China's building industry were 34.41%, 32.07%, 19.05% and 8.72%, respectively.Thus, burning diesel oil is the biggest source of direct carbon emission in China's building industry, followed by coal, gasoline, and electricity between 2005 and 2013.

Estimated Indirect Carbon Emission
Using Equation (3) and carbon emission coefficients shown in Table 5, we calculated the indirect carbon emission of China's building industry (see Figure 2).Total direct carbon emission of China's building industry increased from 86.61 million tons of CO2 to 370.37  As shown in Figure 1, the direct carbon emission includes carbon emission from eight type of fuels (coal, coke, crude oil, fuel oil, gasoline, kerosene, diesel oil and natural gas) and electricity of building industry.The main sources of direct carbon emission in China's building industry are diesel oil coal, gasoline, and electricity.In 2005, burning diesel oil, coal, gasoline, and electricity consumption contributions to total direct carbon emission in China's building industry were 37.34%, 37.29%, 15.70% and 5.62%, respectively.In 2013, burning diesel oil, coal, gasoline, electricity consumption contributions to total direct carbon emission in China's building industry were 34.41%, 32.07%, 19.05% and 8.72%, respectively.Thus, burning diesel oil is the biggest source of direct carbon emission in China's building industry, followed by coal, gasoline, and electricity between 2005 and 2013.

Estimated Indirect Carbon Emission
Using Equation (3) and carbon emission coefficients shown in Table 5, we calculated the indirect carbon emission of China's building industry (see Figure 2).Total direct carbon emission of China's building industry increased from 86.61 million tons of CO 2 to 370.37 million tons of CO 2 between 2005 and 2013.The compound annual growth rate of direct carbon emission was 18.50% for this period.It should be noted that direct carbon emission was not always rising.Instead, direct carbon emission decreased from 518.56 million tons of CO 2 in 2012 to 370.37 million tons of CO 2 in 2013.The indirect carbon emission includes five types of building materials: cement, steel, wood, aluminum and glass.As shown in Figure 2, the dominant source of indirect carbon emission in China's building industry is the carbon emission from cement.Because the consumption of building materials is large and their carbon emission coefficient is high, the proportion of indirect carbon emissions is large.

Estimated Total Carbon Emission
Total carbon emission in China's building industry was calculated using Equation (3).As shown in Figure 3, total carbon emission in China's building industry increased from 984.69 million tons of CO2 in 2005 to 3753.83 million tons of CO2 in 2013.The compound annual growth rate of total carbon emission was 18.21%, which was close to the compound annual growth rate of direct carbon emissions.The overwhelming dominant source of total carbon emission was indirect carbon emission, which accounted for 96%-99% of total carbon emission from China's building industry during 2005-2013.Million tons of CO2 The indirect carbon emission includes five types of building materials: cement, steel, wood, aluminum and glass.As shown in Figure 2, the dominant source of indirect carbon emission in China's building industry is the carbon emission from cement.Because the consumption of building materials is large and their carbon emission coefficient is high, the proportion of indirect carbon emissions is large.

Steel carbon emission Wood carbon emission Cement carbon emission Aluminum carbon emission Glass carbon emission
In 2005, carbon emission from cement, steel, wood, aluminum and glass consumption produced 56.64%, 33.69%, 7.08%, 2.36% and 0.24% of total indirect carbon emission in China's building industry, respectively.In 2013, carbon emission from cement, steel, wood, aluminum and glass consumption contributed to total direct carbon emission in China's building industry were 52.80%, 35.91%, 6.86%, 3.62%, and 0.81%, respectively.

Estimated Total Carbon Emission
Total carbon emission in China's building industry was calculated using Equation (3).As shown in Figure 3, total carbon emission in China's building industry increased from 984.69 million tons of CO 2 in 2005 to 3753.83 million tons of CO 2 in 2013.The compound annual growth rate of total carbon emission was 18.21%, which was close to the compound annual growth rate of direct carbon emissions.The overwhelming dominant source of total carbon emission was indirect carbon emission, which accounted for 96-99% of total carbon emission from China's building industry during 2005-2013.

Decomposition Analysis
Inspired by earlier studies [66][67][68][69][70][71][72][73][74][75], the total changes in carbon emissions ∆C is decomposed into the four indictors: ∆C (the effect of energy structure), ∆C (the effect of energy intensity), ∆C (the effect of industrial scale), and ∆C (the effect of indirect carbon emission intensity).Using Equations ( 11)-( 17), we qualify effects of energy structure, energy intensity, economy, and indirect emission on change in total carbon emission from China's building industry between 2005 and 2013.The results are shown in Figure 4.

Economic Effects
As shown in Figure 4, economic effects (economic output from building industry) were the biggest contributor to the increase in carbon emission.During 2005-2013, economic effect contributed to increase carbon emission by 71.22%.Economic effects have always taken a positive role in increasing carbon emission.However, it should also be noted that economic effects became the second biggest contributor after indirect emission intensity since 2009.

Decomposition Analysis
Inspired by earlier studies [66][67][68][69][70][71][72][73][74][75], the total changes in carbon emissions ∆C is decomposed into the four indictors: ∆C St (the effect of energy structure), ∆C It (the effect of energy intensity), ∆C Qt (the effect of industrial scale), and ∆C Pt (the effect of indirect carbon emission intensity).Using Equations ( 11)-( 17), we qualify effects of energy structure, energy intensity, economy, and indirect emission on change in total carbon emission from China's building industry between 2005 and 2013.The results are shown in Figure 4.

Economic Effects
As shown in Figure 4, economic effects (economic output from building industry) were the biggest contributor to the increase in carbon emission.During 2005-2013, economic effect contributed to increase carbon emission by 71.22%.Economic effects have always taken a positive role in increasing carbon emission.However, it should also be noted that economic effects became the second biggest contributor after indirect emission intensity since 2009.

Decomposition Analysis
Inspired by earlier studies [66][67][68][69][70][71][72][73][74][75], the total changes in carbon emissions ∆C is decomposed into the four indictors: ∆C (the effect of energy structure), ∆C (the effect of energy intensity), ∆C (the effect of industrial scale), and ∆C (the effect of indirect carbon emission intensity).Using Equations ( 11)-( 17), we qualify effects of energy structure, energy intensity, economy, and indirect emission on change in total carbon emission from China's building industry between 2005 and 2013.The results are shown in Figure 4.

Economic Effects
As shown in Figure 4, economic effects (economic output from building industry) were the biggest contributor to the increase in carbon emission.During 2005-2013, economic effect contributed to increase carbon emission by 71.22%.Economic effects have always taken a positive role in increasing carbon emission.However, it should also be noted that economic effects became the second biggest contributor after indirect emission intensity since 2009.

Indirect Emission Intensity Effects
Generally, indirect emission intensity (indirect carbon emission economic output of building industry) effects are the second contributor to increase in total carbon emission of China's building industry.From 2005 to 2013, the accumulated contributing rate of indirect emission effects to increase total carbon emission reached 29.66%.However, the contribution from indirect emission intensity was not always positive.Indeed, indirect emission intensity effects offset the increase in carbon emission during 2005-2008, 2009-2010, and 2012-2013.During 2010-2012, indirect emission intensity offset became the leading contributor to increase in carbon emission.The change of indirect emission intensity effects might be related to the massive RMB 4 trillion (~US$0.6trillion) infrastructure plan, which was proposed to deal with the 2008 global finance crisis in November 2008.Such rapid large-scale infrastructure investment might lead to inefficient material consumption.Indirect carbon emission intensity (indirect carbon emission per unit of GDP) increased from 0.96 kgCO 2 /Yuan in 2009 to 1.07 kg CO 2 /Yuan in 2010, to 1.66 kg CO 2 /Yuan in 2011, and further to 2.05 kg CO 2 /Yuan in 2012.Fortunately, the indirect carbon emission intensity decreased to 1.34 kg CO 2 /Yuan in 2013.The indirect carbon emission intensity was reversed to leading contributor to offset the increase in carbon emission between 2012 and 2013.

Energy Intensity Effects and Energy Structure Effects
Both energy intensity effects and energy structure effects contributed to offset carbon emission.The accumulated contributing rate of energy intensity effects and energy structure effects to increase in carbon emission from 2005 to 2013 were −0.66% and −0.22%, respectively.This is closely related to the energy consumption structure in China's building industry.Coal and oil were the overwhelming dominant sources of energy consumption in China's building industry, whereas clean energy remained a smaller proportion.Given the energy consumption structure has not changed, the energy structure effects and energy intensity effects were minimal.

Decoupling Analysis
Based on former studies [49,54,[76][77][78][79][80][81][82][83][84][85][86][87], we develop decoupling elasticity model and decoupling efforts model.Using Equations ( 18)-( 20), we calculated the decoupling elasticity and decoupling efforts index.As illustrated in Figure 5 The accelerating urbanization and industrialization led to booming of building industry, which means more energy were consumed and more building materials were used.Especially the indirect carbon emission from the building materials is the leading contributor of carbon emission, which is consistent with the estimated indirect carbon emission analysis.We can see in Figure 6 that the change of decoupling effort indexes is consistent with the change of decoupling elasticity of carbon emissions.In addition, it is concluded that the reducing of intensity of indirect carbon emissions is a key factor in decoupling from the construction industry, however, the efforts of the energy structure effect and energy intensity are rarely small, which indicates the current status of unreasonable energy structure and energy intensive industry, and the energy supply is still dominated by high-carbon energy supply when the demand of energy is increasing while the supply of clean low-carbon energy supply cannot keep up with the economic development.

Conclusions
In this paper, we calculated the direct and indirect carbon emission in China's building industry from 2005 to 2013, then analyzed the drivers of carbon emission in China's building industry, and finally estimated the decoupling status of China's building industry.The main conclusions are as follows.
Using data of energy consumption and materials in China's building industry from China's official statistics, and carbon emission coefficient from IPCC, we calculated that the total carbon emission in China's building industry increased from 984.69 million tons of CO2 in 2005 to 3753.98We can see in Figure 6 that the change of decoupling effort indexes is consistent with the change of decoupling elasticity of carbon emissions.In addition, it is concluded that the reducing of intensity of indirect carbon emissions is a key factor in decoupling from the construction industry, however, the efforts of the energy structure effect and energy intensity are rarely small, which indicates the current status of unreasonable energy structure and energy intensive industry, and the energy supply is still dominated by high-carbon energy supply when the demand of energy is increasing while the supply of clean low-carbon energy supply cannot keep up with the economic development.We can see in Figure 6 that the change of decoupling effort indexes is consistent with the change of decoupling elasticity of carbon emissions.In addition, it is concluded that the reducing of intensity of indirect carbon emissions is a key factor in decoupling from the construction industry, however, the efforts of the energy structure effect and energy intensity are rarely small, which indicates the current status of unreasonable energy structure and energy intensive industry, and the energy supply is still dominated by high-carbon energy supply when the demand of energy is increasing while the supply of clean low-carbon energy supply cannot keep up with the economic development.

Conclusions
In this paper, we calculated the direct and indirect carbon emission in China's building industry from 2005 to 2013, then analyzed the drivers of carbon emission in China's building industry, and finally estimated the decoupling status of China's building industry.The main conclusions are as follows.
Using data of energy consumption and materials in China's building industry from China's official statistics, and carbon emission coefficient from IPCC, we calculated that the total carbon emission in China's building industry increased from 984.69 million tons of CO2 in 2005 to 3753.98

Conclusions
In this paper, we calculated the direct and indirect carbon emission in China's building industry from 2005 to 2013, then analyzed the drivers of carbon emission in China's building industry, and finally estimated the decoupling status of China's building industry.The main conclusions are as follows.
Using data of energy consumption and materials in China's building industry from China's official statistics, and carbon emission coefficient from IPCC, we calculated that the total carbon emission in China's building industry increased from 984.69 million tons of CO 2 in 2005 to 3753.98 million tons of CO 2 in 2013.The average annual growth rate is 18.21% per year.Indirect carbon emission from building material consumption accounted for 96-99% of total carbon emission.
Using LMDI technique, we qualify the four key influencing factors for carbon emission in China's building industry.The indirect emission intensity effect was leading contributor to change of carbon emission.It was followed by economic output effects, which always contributed to increase carbon emission.Energy intensity effect and energy structure effect took a negligible role to offset carbon emission.
The status between carbon emission and economic output in China's building industry during 2005-2006 and during 2007-2008 was weak decoupling; during 2006-2007 and during 2008-2010 was expansive decoupling; and during 2010-2013 was expansive negative decoupling.Indirect carbon intensity decoupling index was a leading contributor to the total decoupling index in China's building industry.It was followed by the energy structure and energy intensity decoupling index.

Policy Implication
Based on the above analysis, three policy recommendations are offered to decouple China's building industry from carbon emission (Figure 7).

Policy Implication
Based on the above analysis, three policy recommendations are offered to decouple China's building industry from carbon emission (Figure 7).(1) Reducing the indirect emission intensity: Above all, the reduction of indirect emission intensity is a key to delinking economic output from carbon emission, given that indirect emission is the overwhelming dominant source of carbon emission in China's building industry.The measures to reduction of indirect emission intensity include, but are not limited to: (i) development of new building materials to reduce the consumption of traditional building materials, such as cement, steel, and aluminum; (ii) improving energy efficiency to lower carbon intensity of traditional building materials; and (iii) phasing out the low energy efficient building materials as soon as possible.(2) Reducing energy intensity: As shown in our study, energy intensity effects were leading contributor to offset carbon emission in China's building industry.Improving energy efficiency is a cost-effective approach to decouple between economic output and carbon in China's building industry.The government should introduce policies and establish financial support systems to promote the development of low-carbon technologies, and encourage construction companies to adopt low-carbon construction technology to optimize building design, thereby improving energy efficiency and improving the suppression effect of energy intensity on carbon emission.(3) Optimizing energy structure: We can fully develop the use of hydropower, wind energy, solar energy and other clean energy, reduce dependence on high-carbon energy, and establish a sound energy-saving emission reduction standard building system.
On further deepening the northern heating area of existing residential building heating metering and energy conservation work notice During the Twelfth Five-Year Guideline, the Ministry of finance, and department of housing and urban rural development will further intensify efforts to improve the relevant policies to carry out heating metering and energy conservation work.December 2011 "Housing Ministry of Urban and Rural Construction on the implementation of the" State Council on the issuance of "the Twelfth Five-Year Guideline" energy-saving emission reduction comprehensive work program notice "implementation plan" This program requires all levels of housing urban and rural construction departments to fully understand the housing urban and rural areas in the field of energy conservation and emission reduction work of the importance and urgency, establish a high degree of political responsibility and sense of mission, strengthen cooperation with relevant departments, solid work to ensure Complete the task of energy-saving emission reduction.January Forward the development and reform of the Ministry of Housing and Urban Construction "Green Building Action Program" noticeIn order to thoroughly implement the scientific concept of development, effectively transform the urban and rural construction mode and the development of the construction industry, improve the efficiency of resource utilization, achieve energy conservation and emission reduction targets, and actively respond to global climate change, build a resource-saving and environment-friendly society, Civilized level, improve people's quality of life.
The compound annual growth rate of direct carbon emission was 18.50% for this period.It should be noted that direct carbon emission was not always rising.Instead, direct carbon emission decreased from 518.56 million tons of CO2 in 2012 to 370.37 million tons of CO2 in 2013.

Figure 3 .
Figure 3. Direct, indirect and total carbon emission from China's building industry between 2005 and 2013.

Figure 3 .
Figure 3. Direct, indirect and total carbon emission from China's building industry between 2005 and 2013.
, the growth rate of carbon emission and economical outputs, and the decoupling elasticity values of economic outputs are positive during the whole period.The values of Decoupling elasticity (e) is less than 0.8 in 2006 and 2008; the e is between 0.8 and 1.2 in 2007 and 2010; and the e is more than 1.2 in 2009 and 2011-2013.Consequently, the economic outputs decoupling states exhibit weak decoupling in 2006 as well as 2008, expansive decoupling in 2007 as well as 2010, and turn into expansive negative decoupling in 2009 and during 2011-2013.That means the growth rate of carbon emission is slower than the growth rate of economical outputs in 2006, 2008 and 2010, however, the growth rate of carbon emission is faster than the growth rate of economical outputs in 2007, 2009 and during 2011-2013, which is mainly attributed to the economy increase in China mainly depending on the infrastructure.The 2008-2009 Chinese economic stimulus plan is a US$586 billion stimulus package announced by the State Council of the People's Republic of China as an attempt to minimize the impact of the global financial crisis; in addition, China has experienced urbanization and industrialization.Its urbanization and industrialization has been accelerated in the past decade.

Figure 5 .
Figure 5.The change of decoupling elasticity of carbon emissions during 2006-2013.

Figure 5 .
Figure 5.The change of decoupling elasticity of carbon emissions during 2006-2013.
CO2 in 2013.The average annual growth rate is 18.21% per year.Indirect carbon emission from building material consumption accounted for 96-99% of total carbon emission.Using LMDI technique, we qualify the four key influencing factors for carbon emission in China's building industry.The indirect emission intensity effect was leading contributor to change of carbon emission.It was followed by economic output effects, which always contributed to increase carbon emission.Energy intensity effect and energy structure effect took a negligible role to offset carbon emission.The status between carbon emission and economic output in China's building industry during 2005-2006 and during 2007-2008 was weak decoupling; during 2006-2007 and during 2008-2010 was expansive decoupling; and during 2010-2013 was expansive negative decoupling.Indirect carbon intensity decoupling index was a leading contributor to the total decoupling index in China's building industry.It was followed by the energy structure and energy intensity decoupling index.

Figure 7 .
Figure 7.The suggestions based on the data analysis.

Figure 7 .
Figure 7.The suggestions based on the data analysis.

Table 2 .
The buildings code and regulation for energy efficiency in different countries.National supervision and random in section is one method of maintaining product quality by the State.Regular supervision and random inspections are conducted every quarter, and irregular supervision and inspections are conducted according to the status of the product quality.
Product certifications adopt the principal of voluntarism.The method stipulates certification conditions, procedures, usage of energy conservation marks, and treatment after certification.It promotes key energy conservation sectors during the "11th Five-Year Plan": industry, traffic and transportation, commercial and civil applications.The Plan also puts forward the organization and implementation of key energy conservation projects, such as modification of industrial coal-burning boilers, regional combined heat and power generation, utilization of excessive heat and pressure, saving and replacing oil, energy conservation of buildings, a green lighting project, establishment of energy conservation monitoring and a technical service system, etc.

Table 3 .
The carbon coefficients of different kinds of energy.

Table 4 .
The carbon coefficients of electricity.

Table 5 .
The carbon coefficients of consumption construction materials.
Total direct carbon emission of China's building industry increased from 32.06 million tons of CO 2 in 2005 to 50.12 million tons of CO 2 in 2013.The compound annual growth rate of direct carbon emission in China's industry was 5.74% during 2005-2013.