Reduction In Life-cycle Emissions Research Articles

Eco-Energetical analysis of circular economy and community-based virtual power plants (CE-cVPP): A systems engineering-engaged life cycle assessment (SE-LCA) method for sustainable renewable energy development

Amidst the escalating complexity of energy demands and climate concerns, natural calamities, and the Black Swan phenomenon have all presented formidable obstacles to the advancement and implementation of renewable energy sources. In light of the present backlog of studies in energy technology, the three primary issues identified and resolved in this study are inadequate analysis of the actual situation, absence of evidence of sustainable development, and flawed systematic methodology. This study proposes a novel renewable energy development initiative known as the circular economy and community-based virtual power plant (CE-cVPP). By integrating community participation and circular economy principles, this initiative aims to foster sustainable development and facilitate resilient progress. The principal focuses of the model are community renewable energy supply, energy demand, and community participation management. The sustainable framework is constructed upon the principles of circular economy theory. The systems engineering-based life cycle assessment (SE-LCA) method is proposed as an innovative approach to whole life cycle assessment that is grounded in systems engineering. Its purpose is to facilitate a systematic implementation and empirical evaluation of the sustainability of energy, the environment, and the economy. On the basis of disparities in renewable energy sources and a variety of spatiotemporal dimensions, CE-cVPP is categorised into four representative groups. We present a business community model for energy and environmental analysis that is based on a hospital in Harbin. The results suggest that the overall lifecycle primary energy conservation rate is 67.21%, which is an exceptional outcome that significantly promotes sustainable development in comparison to conventional methods. This improves environmental and human health protection as the full lifecycle emission reduction ratios for atmospheric pollutants are 53.50% (SO2-eq.), 51.69% (PM2.5-eq.), and 74.85% (CO2-eq.). Consideration is given to raw materials, equipment construction, equipment operation, tariffs on six pollutants, and material recycling when calculating the total cost. The annual total cost savings ratio for the full lifecycle is 54.21% when compared to the traditional system. This research possesses methodological and theoretical applicability to the energy and power sectors.

Economic and environmental comparison of emerging plastic waste management technologies

Recovery of plastics may need to move beyond traditional mechanical methods and adopt emerging recycling processes including dissolution/precipitation, solvolysis, and pyrolysis. We investigate the costs and climate impacts of optimal solid waste management (SWM) strategies when deploying emerging recycling processes. Introducing a mix of emerging recycling technologies can reduce SWM system costs, increase plastic recycling rates, and potentially help SWM systems achieve net reductions in life cycle emissions. Recycling programs that rely solely on traditional mechanical recycling incur higher system costs, but can achieve the lowest life cycle emissions, regardless of whether the rejected plastic streams are landfilled or treated in waste-to-energy. In a future with increased recycling, SWM systems that utilize fully commercialized dissolution/precipitation and chemical recycling can further improve the cost advantage and the emission reduction potential. The sensitivity analysis demonstrates that enhancing waste collection and refining emerging recycling technologies can considerably increase the economic and environmental performance of SWM.

Full life cycle emission reduction potential of ultra-low emission transformation in China's cement industry

China accounts for more than 50% of the global total cement production, the emission of pollutants in the cement industry occupies a large proportion of the industries. Some provinces have first carried out in-depth treatment of the cement industry, and the national level will also introduce an implementation plan for ultra-low emission transformation of the cement industry to promote continuous improvement of China's air quality. In this work, a pollutant emission inventory covering the full life cycle of the cement industry, including organized emission, unorganized emission and transportation, was established based on pollutant discharge permit, Continuous Emission Monitoring System (CEMS) database and field investigation. And, the emission reduction potential of particulate matter (PM), sulfur dioxide (SO2) and nitrogen oxide (NOx) after the implementation of ultra-low emission transformation in cement industry was evaluated. The results show that the existing dedusting, desulphurization and denitration technologies can control the concentrations of PM, SO2 and NOx below 10 mg/m3, 35 mg/m3 and 50 mg/m3, respectively. The emission reduction potential of PM, SO2 and NOx in cement industry is 259.54 kt, 14.98 kt and 607.04 kt, corresponding emission reduction ratio is 37%, 24% and 64%, respectively. In addition, this work reveals the spatial characteristics of pollutant emission level and emission reduction potential of the cement industry, which is conducive to the rational layout of ultra-low emission transformation, and push forward the transformation task by area and stage.

Life Cycle Greenhouse Gas Emissions of CO2-Enabled Sedimentary Basin Geothermal.

The expansion of renewable energy and the large-scale deployment of carbon dioxide (CO2) capture and storage (CCS) can decarbonize the power sector. The use of CO2 to extract geothermal heat from naturally porous and permeable sedimentary basins to generate electricity (CO2-plume geothermal (CPG) system) presents an opportunity to simultaneously generate renewable energy and geologically store CO2. In this study, we estimate the life cycle greenhouse gas (GHG) impacts of CPG systems through 12 scenarios in which CPG systems are combined with one of six CO2 sources (e.g., bioenergy with carbon capture and storage (BECCS) and iron and steel facilities) and operate in two geological settings. We find the life cycle GHG emissions of CPG systems ranging from -0.25 to -6.18 kg CO2eq/kWh. CPG systems can achieve the highest emissions reductions when utilizing the CO2 captured from BECCS. We evaluate uncertainty through a Monte Carlo simulation, demonstrating consistent net reductions in life cycle emissions and a local, one-parameter-at-a-time sensitivity analysis that identifies the CO2 capture capacity as the high-impact parameter of the results. Through the production of electricity, CPG systems can provide additional environmental benefits to the deployment of large-scale CCS.

Comparative life cycle greenhouse gas analysis of clean hydrogen pathways: Assessing domestic production and overseas import in South Korea

The development of a Clean Hydrogen Standard based on life-cycle greenhouse gas (GHG) emissions is gaining prominence on the international agenda. Thus, a framework for assessing life-cycle GHG emissions for clean hydrogen pathways is necessary. In this study, the comprehensive datasets and effects of various scenarios encompassing hydrogen production, carriers (liquid hydrogen, ammonia, methylcyclohexane), carbon capture and storage (CCS), target analysis year (2021, 2030) to reflect trends of greening grid electricity and potential import countries on aggregated life-cycle GHG emissions were presented. South Korea was chosen as a case study region, and the low-carbon alternatives were suggested for reducing aggregated emissions to meet the Korean standard (5 kgCO2e/kgH2). First, capturing and storing nearly entire (>90%) CO2 from fossil- and waste-based production pathways is deemed essential. Second, when repurposing the use of hydrogen that was otherwise used internally, applying a penalty for substitution is appropriate, leading to results notably exceeding the standard. Third, for electrolysis-based hydrogen, using renewable or nuclear electricity is essential. Lastly, when hydrogen is imported, in a well-to-point-of-delivery (WtP) perspective, using renewable electricity during hydrogen conversion into a carrier and reusing the produced hydrogen for endothermic reconversion reaction are recommended. By implementing the developed calculation framework to other countries' cases, it was observed that importing hydrogen to regions having scope of WtP or above (e.g., well-to-wheel) might not meet the threshold due to additional emissions from importation processes. Additionally, for hydrogen carriers undergoing the endothermic reconversion, the approach to reduce WtP emissions (reusing produced hydrogen) may conflict with the approach to reduce well-to-gate (WtG) emission (using external fossil-based fuel). The discrepancy highlights the need to set a broader scope of emissions assessment to effectively promote the life-cycle emission reduction efforts of hydrogen importers. This study contributes to the field of clean hydrogen GHG emission assessment, offering a robust database and calculation framework while addressing the effects of greening grid electricity and CCS implementation, proposing low-carbon alternatives and GHG assessment scope to achieve global GHG reduction.

Research on the Whole Lifecycle Emission Reduction Effect of Buildings with Different Structures in Severely Cold Regions—A Case Study in China

Since the construction industry is one of China’s high carbon emission industries, to achieve China’s carbon neutrality target by 2060, CO2 emissions in cold regions must be reduced. At the same time, forests have excellent carbon sequestration abilities, so this paper takes residential buildings in severely cold regions as the object of carbon emission reduction research. A model of a two-story building in Changchun was constructed, and the life-cycle carbon emissions of reinforced concrete and wood structures were measured using the life-cycle evaluation method as the basis for calculation and simulation with DesignBuilderVer.7 software. The results show that the life-cycle carbon emission of a wood structure house is 61.46 t less than that of a reinforced concrete house, and the life-cycle carbon emission reduction rate of a wood structure house is 43.39%. Based on the data, it has been proven that wooden structures effectively reduce carbon dioxide emissions during the building life cycle while enhancing building performance, given the same structural conditions.

Carbon footprint of low-energy buildings in the United Kingdom: Effects of mitigating technological pathways and decarbonization strategies

There is a limited comprehensive analysis of the effectiveness of adopted carbon mitigation strategies for buildings over their life cycle, that are concerned with temporal perspectives of emissions. Accordingly, this paper explores a life cycle assessment (LCA) to address the concerns regarding mitigating the carbon footprint of a UK timber-frame low-energy dwelling. In particular, it aims to investigate the potential greenhouse gas (GHG) emission reduction in terms of three different heating and ventilation options, and to analyze the influence of decarbonization of electricity production as well as the technological progress of the waste treatment of timber on the building's environmental performance. Thus, the whole life‑carbon of the building case studies was evaluated for a total of eight investigated prospective scenarios, and they were compared to the LCA results of the baseline scenario, where the existing technology and context remained constant over time. Results show that using a compact heat pump would lead to a significant whole life-cycle emission reduction of the dwelling, by 19 %; while GHG emission savings can be reinforced if the assessed systems are employed simultaneously with grid decarbonization, exhibiting a 25 %–60 % reduction compared to the baseline scenario. Moreover, technological changes in the waste treatments of timber products could substantially reduce the buildings' embodied emissions, representing 3 %–23 %. From these emission-saving measures, the contribution of material efficiency strategies to achieve more embodied carbon savings should be highlighted in future construction practices.

Benefit analysis of multi-approach biomass energy utilization toward carbon neutrality

To reduce greenhouse gas (GHG) emissions, biomass has been increasingly developed as a renewable and clean alternative to fossil fuels because of its carbon-neutral characteristics. China has been investigating the rational development and use of bioenergy for developing its clean energy and achieving carbon neutrality. Substituting fossil fuels with multi-source and multi-approach utilized bioenergy and corresponding carbon reduction in China remain largely unexplored. Here, a comprehensive bioenergy accounting model with a multi-dimensional analysis was developed by combining spatial, life cycle, and multi-path analyses. Accordingly, the bioenergy production potential and GHG emission reduction for each distinct type of biomass feedstock through different conversion pathways were estimated. The sum of all available organic waste (21.55 EJ yr-1) and energy plants on marginal land (11.77 EJ yr-1) in China produced 23.30 EJ of bioenergy and reduced 2,535.32 Mt CO2-eq emissions, accounting for 19.48% and 25.61% of China's total energy production and carbon emissions in 2020, respectively. When focusing on the carbon emission mitigation potential of substituting bioenergy for conventional counterparts, bioelectricity was the most effective, and its potential was 4.45 and 8.58 times higher than that of gaseous and liquid fuel alternatives, respectively. In this study, life cycle emission reductions were maximized by a mix of bioenergy end uses based on biomass properties, with an optimal 78.56% bioenergy allocation from biodiesel, densified solid biofuel, biohydrogen, and biochar. The main regional bioenergy GHG mitigation focused on the Jiangsu, Sichuan, Guangxi, Henan, and Guangdong provinces, contributing to 31.32% of the total GHG mitigation potential. This study provides valuable guidance on exploiting untapped biomass resources in China to secure carbon neutrality by 2060.

Analyzing the evolution trend of energy conservation and carbon reduction in transportation with promoting electrification in China

Promoting electrical transition in vehicle industry has become one of the main objectives for transportation sectors nowadays. However, no consensus has been reached as to whether the penetration of electric vehicles (EVs) have superiority in energy conservation and carbon reduction with life-cycle thinking. Consequently, this paper applies network evolutionary game theory to investigate the evolution trend of industry energy conservation and carbon reduction with promoting electrification in China. To fit the real decision-making environment faced by manufacturers, the greenness competition interactions, competitive strategy invasion, and market uncertainty are further considered under the impact of dual credit policy. Results show that implementing dual credit policy makes electrical transition an irreversible trend for manufacturers, but it does not mean that internal combustion engine vehicle will disappear, rather, it coexists with EVs in a certain proportion, which is negatively related to consumer's acceptance toward EVs. Meanwhile, to address energy conservation and carbon reduction, manufacturers should be encouraged to choose a fuel reduction strategy to decelerate the industry electrification trend, thus acquiring better energy conservation performances. And before increasing consumer's acceptance toward EVs, increasing the proportion of renewable source in primary energy warrants greater urgency and effectiveness to achieve life-cycle emission reduction advantage of EVs.

Energy, economic and environmental (3E) analysis for the renewable jet fuel production process

Blending conventional petroleum jet fuel with renewable fuel obtained from hydro-processing of cooking oil wastes can significantly reduce the carbon footprint of the aviation sector. Renewable jet fuel (RJF) remains for the most part more expensive than conventional jet fuel and the life-cycle emissions reduction depends on the feedstock. For promoting mass production of used cooking oil (UCO) based jet fuel, a 3E (energy/exergy, environmental and economic) analysis of a simulated processing plant is carried out. Hydrogen is the main component in the two-step process: hydro-processing and hydro-cracking/isomerization. Hydrogen production and exergy destruction in the process significantly influence the life-cycle emissions of the RJF. The low exergy efficiency of the process units where significant heat transfer occurs generates an increase in the price of the products. Results show a life-cycle carbon dioxide emissions reduction from 41 % to 81 % when combusting the hydro-processed jet fuel instead of conventional jet fuel. The minimum fuel selling price could be very close to conventional jet fuel (about 18 % more expensive) if an effective cooking oil wastes collection system is in place. Moreover, when implementing a carbon tax above $37/tCO 2 the price becomes equal to conventional jet fuel. UCO is the most sustainable feedstock as there is no competition with the food market and the environmental benefits justify government spending for promoting mass production.

Beyond Operational Energy Efficiency: A Balanced Sustainability Index from a Life Cycle Consideration

Most deep energy renovation projects focus only on an operating energy reduction and disregard the added embodied energy derived from adding insulation, window/door replacement, and mechanical system replacement or upgrades. It is important to study and address the balance and trade-offs between reduced operating energy and added embodied energy from a whole life cycle perspective to reduce the overall building carbon footprint. However, the added embodied energy and related environmental impact have not been studied extensively. In response to this need, this paper proposes a holistic sustainability index that balances the trade-off between reduced operating energy and added embodied energy. Eight case projects are used to validate the proposed method and calculation. The findings demonstrate that using a balanced sustainability index can reveal results different from a conventional operating energy-centric approach: (a) operating energy savings can be offset by the embodied energy gain, (b) the operating energy savings do not always result in a life cycle emissions reduction, and (c) the sustainability index can vary depending on the priorities the decision makers give to operating carbon, embodied carbon, and operating cost. Overall, the proposed sustainability score can provide us with a more comprehensive understanding of how sustainable the renovation works are from a life cycle carbon emissions perspective, providing a more robust estimation of global warming potential related to building renovation.

A generalized framework for analyzing car lifetime effects on stock, flow, and carbon footprint

AbstractThis study proposes a new framework for estimating the effects of changes in the physical lifespan (PHL) of cars and the possession lifespan (POL) of new and used cars on stock, flow, and carbon footprint (CF). Applying this framework to all new and used cars registered in Japan from 1990 to 2016 showed that a 10% extension of the PHL of cars reduced the CF of cars by 30.7 Mt, while a 10% extension of the POL of new cars reduced the CF of cars by 26.4 Mt, and a 10% extension of the POL of used cars produced a 5.2 Mt CF reduction. On the other hand, a 10% lifetime reduction in the three cases increased CF by 42.2, 29.4, and 6.0 Mt, respectively. These results indicate that increasing the lifetime of new and used cars could contribute significantly to the mitigation of global warming. To achieve a large reduction in life cycle emissions, car designers should focus on ways to extend vehicle lifetimes.

Applying the handprint approach to assess the air pollutant reduction potential of paraffinic renewable diesel fuel in the car fleet of the city of Helsinki

Abstract Ambient air pollution is a global environmental challenge, especially in densely populated regions. In urban areas, road traffic is an important source of fine particulate matter (PM2.5) and nitrogen oxide (NOx) emissions, primarily due to exhaust gases. The adoption of paraffinic renewable diesel fuels for urban transportation has been suggested as a more sustainable and less air polluting alternative to conventional fossil fuels. The aim of this study is, therefore, to examine whether the transition from the conventional fossil fuel diesel to paraffinic renewable diesel (hydrotreated vegetable oil [HVO] according to the EN 15940 standard) can reduce PM2.5 and NOx emissions in an urban environment. The life cycle assessment-based handprint approach is utilized to calculate and demonstrate the emissions reduction. The reduction potential is quantified for Euro 4, 5 and 6 passenger diesel cars using actual car fleet, mileage, local temperature, and laboratory emissions measurements for 2018 in Helsinki, Finland. Our study shows that the use of HVO can reduce PM2.5 and NOx emissions in urban areas. According to our results, PM2.5 emissions could be reduced by 49% for the defined location and car fleet by replacing conventional fossil-fuel diesel with HVO. In the case of NOx emissions, the local reduction potential is 7%. Overall life cycle emissions reduction potentials of NOx and PM2.5 emissions are 11% and 44%, respectively, if conventional diesel is replaced by HVO. Thus, the manufacturer of HVO can communicate the air quality handprint, and in particular, the NOx and PM2.5 handprints, that their product can achieve.

Reduction of Environmental Impacts Due to Using Permeable Pavements to Harvest Stormwater

While rainwater harvesting can provide additional water resources, this approach is largely undertaken using water from roofs. More recently, the potential for using stormwater harvested from permeable pavements was recognised as a potential additional water resource. The objective of this study was to estimate the reduction of environmental impacts caused by traditional drainage systems and centralised water utilities if permeable pavement systems were used to harvest stormwater for nonpotable purposes in buildings. The lifecycle environmental impacts and costs associated with the proposed pavements and hydraulic systems were assessed. The city of Glasgow was chosen as a case study. We used the Netuno computer programme to estimate the potential for potable water savings considering the use of stormwater for nonpotable purposes and the SimaPro software to perform a lifecycle assessment (LCA). With the implementation of permeable pavements and stormwater utilisation, great reductions in lifecycle emissions (i.e., CO2-, SO2-, and PM2.5-equivalent emissions) were observed. The proposed system also proved to be economically feasible, i.e., a payback period equal to 16.9 years. The results show the economic and environmental feasibility of permeable pavements when used on a large scale, proving to be an important strategy to reduce water and environmental stresses caused by centralised water utilities and traditional drainage systems.

To retrofit or not? Making energy retrofit decisions through life cycle thinking for Canadian residences

Improving the energy performance of buildings has been a much-discussed topic over the past few decades. With the current focus on climate change mitigation, emissions reduction has also come to the forefront of this discussion. Retrofitting is an option to improve the energy and emissions performance of buildings. However, in the residential building stock, retrofit planning for existing buildings faces many complexities due to variations in climatic conditions and macro-environment as well as the presence of multiple stakeholder groups. Thus, in identifying solutions, it is necessary to take a holistic perspective that covers these different dimensions. In this paper, commonly used building energy retrofits were evaluated through a life cycle thinking approach. The performance of various retrofit options applicable for single family detached housing were evaluated using the HOT2000 energy simulation software package under the varying climatic conditions and energy supply scenarios across Canada. The retrofits were evaluated in terms of the additional investment, energy use and cost reduction achieved over the life cycle, and life cycle emissions reduction. The findings indicate that the provincial energy mix and the heating system of the house (i.e. electric or natural gas) play a major role in determining the effectiveness of a retrofit, and this “effectiveness” changes at different stakeholder levels. However, not all retrofits that reduce emissions make economic sense and vice versa when life cycle thinking comes into play. The findings will be useful for building owners and occupants as well as for policy developers and other decision makers interested in demand side management.

BIM-based life cycle environmental performance assessment of single-family houses: Renovation and reconstruction strategies for aging building stock in British Columbia

The building sector accounts for 40% of the energy use and one-third of the greenhouse gas (GHG) emissions globally. Buildings deteriorate with age, which leads to a decrease in their energy performance. Therefore, it is significant to improve the energy performance of aging building block although it is challenging. The two main decision paths for municipalities are renovation and reconstruction. This study investigated the above options for the older housing stock in a densely populated urban centre in British Columbia, Canada. A scenario-based analysis approach was taken to evaluate the life cycle GHG emissions of six different renovation and reconstruction scenarios. The total life cycle emissions were calculated for each scenario including the embodied and operational emission, and the emissions from building construction and maintenance. A BIM-LCA combined approach was used to assess the embodied GHG emissions with the SimaPro software. HOT2000 software was used to model the operational GHG emissions. The results show that in the reconstruction scenarios, around 40% of the emissions are from the material manufacturing stage. The embodied emissions generated from the reconstruction scenarios are 5–6 times higher than the renovation scenarios. The life cycle GHG emissions of the existing house can be reduced by applying renovations, with the emissions saving gradually increasing with the level of retrofitting. The passive house reconstruction scenario delivers the greatest benefit in terms of life cycle emissions reduction compared to all other scenarios. In terms of the GHG emission intensity per unit area, the newly-built houses in scenarios 5 and 6 also have lower life cycle GHG emission per square meter than the renovated existing houses in scenario 1–4 after 15 and 10 years to breakeven respectively. Based on this, it can be concluded that when considering the older existing building stock, a careful weighing of options must take place before making the decision on replacing them with new construction. However, it is also important to consider the economic and social aspects before making decisions to renovate or replace existing houses. The study outcomes will support city planners and urban development planners to make decisions on BC aging building stock development, especially in high population density neighbourhoods.

By-product hydrogen from steam cracking of natural gas liquids (NGLs): Potential for large-scale hydrogen fuel production, life-cycle air emissions reduction, and economic benefit

Steam crackers convert hydrocarbon feedstock (e.g., natural gas liquids) to light olefins via thermal cracking and produce hydrogen as a by-product during the process. Benefiting from the shale gas boom in recent years, the overall production capacity of U.S. steam crackers, as well as the potential of by-product hydrogen production, is continuously growing. We estimate that 3.5 million tonne/year of by-product hydrogen can be produced from steam crackers, almost doubling the size of the existing U.S. merchant hydrogen market. We also find that producing hydrogen from steam crackers creates less (15%–91%) life-cycle greenhouse gas emissions than the conventional centralized steam methane reforming (SMR) pathway. For criteria air pollutants, life-cycle emissions reduction benefits vary greatly (−75% – +85%), depending on the co-product treatment scenario (substitution or allocation) and air pollutant type. The substitution scenario generally results in an increase of criteria air pollutants emissions, mainly due to the requirement of substitutive natural gas fuel. We estimate that the cost of purified by-product hydrogen fuel from steam crackers is $0.9–1.1/kg, reducing hydrogen production costs by 30% compared to the conventional central SMR pathway. Furthermore, using by-product hydrogen from steam crackers can generate credits of $1.8–2.5/kg under California's low-carbon fuel standard.

Carbon emissions and costs associated with subsidizing New York nuclear instead of replacing it with renewables

We compare the cost of maintaining a proposed subsidy for New York's three upstate nuclear power plants with the cost of replacing the plants with renewable technologies from 2016 to 2050. Keeping nuclear operating with subsidy until 2050 is the most expensive option, costing $32.4 billion (2014 USD) over that period in the base business as usual case. The least expensive option is to shut down nuclear today and replace it with onshore wind, saving $7.9 billion. All analyzed renewable scenarios lead to 20.1 to 27.4 Mt CO2 greater life-cycle emission reductions. In addition, re-investing the cost savings of the renewable scenarios into additional onshore wind increase CO2 savings up to 32.5 Mt.

Carbon Footprints of Urban Residential Buildings: A Household Survey-Based Approach

With China’s rapid urbanization process, massive and extensive construction materials are aggregated as stock in urban areas. Understanding the carbon footprints of residential buildings is crucial for achieving the goal of low-carbon cities. In this study, to reveal the emission characteristics of residential buildings regarding carbon footprint, stratified random sampling was developed, and a face-to-face questionnaire was conducted, to obtain critical information on residential buildings and the socio-economic status of 1092 families from 46 communities in Xiamen City, China. The community buildings’ structures were identified, and carbon emissions from the residential buildings were quantified based on analysis of the entire building life cycle. The building life cycle can be divided into six stages: extraction and production; transportation; construction; operation; demolition; and recycling. The household carbon footprints ranged from 0.37 tCO2/year to 22.45 tCO2/year; the per capita carbon footprints ranged from 0.19 tCO2/year to 11.23 tCO2/year. Overall, for the 46 surveyed communities, the average household and per capita carbon footprints were 4.11 tCO2/year and 1.4 tCO2/year, respectively. The total carbon footprints of urban residential buildings were 4.86 MtCO2/year. Analysis of the extraction and production stage revealed that steel recycling could avoid almost 0.05 MtCO2/year. No significant correlations were found between energy use awareness and energy use. The findings can be used by Chinese energy policymakers to understand the views of various energy users, and to re-attune the efforts against these opinions and interests. However, we consider this study a start and not an end to the importance of gauging opinions on energy security from the population of energy users. Nonetheless, awareness campaigns through print and electronic media could be another tool for life cycle emissions reduction in building sector.

High-resolution techno–ecological modelling of a bioenergy landscape to identify climate mitigation opportunities in cellulosic ethanol production

Although dedicated energy crops will probably be an important feedstock for future cellulosic bioenergy production, it is unknown how they can best be integrated into existing agricultural systems. Here we use the DayCent ecosystem model to simulate various scenarios for growing switchgrass in the heterogeneous landscape that surrounds a commercial-scale cellulosic ethanol biorefinery in southwestern Kansas, and quantify the associated fuel production costs and lifecycle greenhouse gas (GHG) emissions. We show that the GHG footprint of ethanol production can be reduced by up to 22 g of CO2 equivalent per megajoule (CO2e MJ–1) through careful optimization of the soils cultivated and corresponding fertilizer application rates (the US Renewable Fuel Standard requires a 56 gCO2e MJ−1 lifecycle emissions reduction for ‘cellulosic’ biofuels compared with conventional gasoline). This improved climate performance is realizable at modest additional costs, less than the current value of low-carbon fuel incentives. We also demonstrate that existing subsidized switchgrass plantings within this landscape probably achieve suboptimal GHG mitigation, as would landscape designs that strictly minimize the biomass collection radius or target certain marginal lands.