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The estimated cities’ contribution to climate change varies depending on the methods chosen by a given city for compiling its greenhouse gas (GHG) emission inventory. This study provides an interpretative synthesis of existing research to explore the differences of three emerging approaches to city-level GHG emissions accounting, based on methodological dimensions: boundary-setting, the categorisation of emissions and the type of emissions. The policy relevance and implications of selecting different system boundaries are explored: each approach can reveal important information which the others fail to identify. This suggests the value of using different and complementary approaches to address as many policy questions and relevant actors possible in climate action planning. Next, key methodological considerations that arise in target-setting approaches involving bringing the emissions balance to zero are presented. An analysis of actual ‘net-zero emission’ concepts used by eight cities reveals that their precise meaning and applicability remain ambiguous. Finally, to improve both the transparency about such metrics and their usability for policy and decision-making, this paper synthesises all key considerations occurring from the analysis of inventorying approaches and net-zero targets into a reporting and communication framework.Policy relevanceMany cities are assuming responsibility for measures to mitigate climate change, but they need greater clarity on ‘climate neutral’ or ‘net-zero’ approaches. Each city’s intended purpose needs careful alignment with a choice of methods. The diverse accounting and target-setting landscape and the associated policy implications are elucidated. This can empower more cities to select appropriate methods and set ambitious targets. Calculation of a GHG emission balance is a means to an end and not the end itself. Its purpose is to show the options for action and measure success. Non-transparent methods involve reputational and ethical risks for city governments. A framework to improve transparency is presented. Dual-accounting approaches involving both production and consumption are now the new trend. Individual actors must be able to identify their influence and potential action scope for mitigating climate change. Agreement is needed on how to approach consumption-based accounting and create more city-specific data.

What is embodied carbon and why is it a significant challenge for clients and designers in the real estate and construction sector? It is the sum of greenhouse gas (GHG) emissions that arise in the life cycle of a building during manufacture and construction (upfront), maintenance and replacement of building components (recurrent), as well as dismantling and waste processing (end of life). Currently, the relative and absolute share of embodied carbon in the life cycle of a single building is growing and becoming a dominant factor in the case of energy-efficient buildings. For example, for new buildings, it can represent more than 50% of life-cycle carbon. Against this background, embodied carbon is becoming an object of assessment not just in research but also in design and decision-making. It also becomes a key action to reduce GHG emissions. Embodied carbon assessment and reduction are being increasingly mandated in national regulations. Clients and designers (as key actors in the supply chain) can harness new knowledge and tools to reduce embodied carbon as part of a strategy to reduce overall GHG emissions. Appropriate methods, data, benchmarks and tools are being further developed and operationalised to support the processes for specifying and designing low carbon buildings. An overview is presented of the state of knowledge and current developments. Constructive recommendations are provided for actions that clients and designers can take.Key findings* From the perspective of a single building’s life cycle, the proportion of embodied carbon is around 50% on average for new energy-efficient buildings. From a macro-economic perspective, approximately 10% of global energy-related CO2 emissions are attributable to the embodied emissions of buildings.* Designers can influence and assess embodied carbon according to related design targets in the client’s brief and/or legal requirements.* A trade-off between operational and embodied carbon is typical, but possibilities exist to optimise both sides.* Embodied carbon can be reduced by selecting low carbon construction products and/or reused building components.* Further possibilities are the revitalisation of existing buildings, the extension of their service life, the minimisation of useable areas (sufficiency), as well as the optimisation of buildings and their components.* With good design, it is possible to construct low embodied carbon buildings with little or no additional costs, and even generate economic benefits.

The urgent need to reduce greenhouse gas emissions and the increasing share of embodied carbon in life-cycle impacts underscore the necessity of mitigating construction and demolition impacts to align with the Paris Agreement. Urban planning significantly influences material flows, with a substantial portion of construction occurring in planned urban development areas (UDAs), such as 76% in Copenhagen, Denmark. However, research on UDAs is limited, with most life-cycle assessments (LCAs) focusing on individual buildings. This study examines the embodied CO2e emissions from buildings and infrastructure in a newly developed UDA, using an archetype-based LCA approach that combines both on-site and average data, which can serve as a stepping stone for a more comprehensive analysis. The study shows that most emissions in the studied UDA occur upfront and are attributed to new building construction. The studied UDA featured several refurbished buildings, repurposed into housing and offices, but their reuse only made a small difference when considering embodied emissions for the entire UDA. Other UDAs may exhibit a different emission profile. Lastly, the study compares neighbourhood and city-scale impacts to absolute environmental boundaries, highlighting the significant climate impacts of urban planning, particularly in UDAs. Policy relevance Urban planning has a significant influence on climate impacts. The substantial amounts of embodied CO2e attributed to planned UDAs, particularly emissions occurring upfront and relative to absolute environmental boundaries, suggest the need to rethink current urban planning frameworks to better align with absolute environmental boundaries and the goals of the Paris Agreement. The results offer insights for developing contextual mitigation measures; the large share of CO2e emitted by new buildings underscores the potential of low-carbon technologies and materials and the broader impact of regulatory targets. Moreover, the limited relative impact of reuse in the studied UDA suggests the need for planning models that prioritise existing building inventories over new construction. Ultimately, the findings may also suggest the need to reconsider the overall scale of permissible building rights altogether.

PURPOSE: Environmental life cycle assessment (LCA) is today an important methodology to quantify the life cycle based environmental impacts of products, services or organisations. Since the very first LCA studies, the cumulative energy demand CED (also called ‘primary energy consumption’) has been one of the key indicators being addressed. Despite its popularity, there is no harmonised approach yet and the standards and guidelines define the cumulative energy demand differently. In this paper, an overview of existing and applied life cycle based energy indicators and a unifying approach to establish characterisation factors for the cumulative energy demand indicator are provided. The CED approaches are illustrated in a building’s LCA case study. METHODS: The five approaches are classified into two main concepts, namely the energy harvested and the energy harvestable concepts. The two concepts differ by the conversion efficiency of the energy collecting facility. A unifying ‘energy harvested’ approach is proposed based on four theses, which ensure consistent accounting among renewable and non renewable energy resources. RESULTS AND DISCUSSION: The indicator proposed is compared to four other CED indicators, differing in the characterisation factors of fossil and biomass resources (upper or lower heating value), the characterisation factor of uranium and the characterisation factors of renewable energy resources (amount harvested or amount harvestable). The comparison of the five approaches is based on the cumulative energy demand of a newly constructed building of the city of Zürich covering the whole life cycle, including manufacturing and construction, replacement and use phase, and end of life. The cumulative energy demand of the life cycle of the building differs between 336 MJ oil-eq/m²a (‘CED uranium low’) and 836 MJ oil-eq/m²a (‘CED energy statistics’). The main differences occur in the use phase. The main reason for the large differences in the results are the different concepts to determine the characterisation factors for renewable and nuclear energy resources. CONCLUSIONS: The energy harvested approach ‘CED standard’ is a consistent approach, which quantifies the energy content of all different (renewable and non-renewable) energy resources. The ‘CED standard’ approach and the impact category indicator results computed with this approach reflect the safeguard subject ‘energy resources’ but not (no other) environmental impacts. The energy harvested approach proposed in this paper can readily be implemented in different contexts and applied to various data sets.

Buildings are major contributors of carbon emissions and related global warming. Emissions occur along all building stages, from a whole-life perspective, including material production, construction processes, building operations, maintenance and end-of-life processes. Upfront emissions include processes before building operations. They can be influenced immediately and will have a positive effect today. However, mitigation potentials during the construction stage are often overseen in research. This study presents an analysis of the carbon emissions of 61 Danish construction sites based on their energy consumption, waste production (module A5) and transport to site (A4). The results show carbon emissions for A4 of 0.28 and for A5 of 1.00 kgCO2e/m2 gross floor area per year over 50 years. This is 13.47% of the Danish whole-life carbon reference of 9.50 kgCO2e/m2y, which includes the product stage (A1–3), replacements (B4), operational energy use (B6) and waste processes and disposal (C3–4). Almost half of the emissions are related to construction waste followed by electricity, heat and fuel. Floor area and building use have not shown to be influential for carbon emissions, suggesting other parameters are more important. The significance of modules A4 and A5 suggests implementing them in future whole-life carbon assessments and related policies. This paper also demonstrates the development of generic emission coefficients, which are suited to increase the feasibility for application in the building industry. Finally, the usability of module A4 and A5 in environmental product declarations is discussed.

In light of the urgent need for climate change mitigation in the construction and real estate sectors, it is crucial to implement effective measures that will drive meaningful progress. Digital tools that support the assessment of buildings’ whole-life carbon emissions play a key role in this effort. However, the successful implementation of these tools relies on their effective and efficient use by various stakeholder groups, each of which has different decision-making needs and workflows. Notably, integrating diverse perspectives into tool quality and service, particularly those of users and developers, remains an under-explored area. This study presents key findings from an international survey conducted across participating countries as part of the IEA EBC Annex 89 project, which focuses on implementing net-zero whole-life carbon buildings. The survey, which is part of a broader set of Annex activities, maps existing tools and analyses aspects such as their capabilities (e.g. the environmental indicators assessed by the tool), information management (e.g. databases) and practical integration (e.g. the format of the data output). This paper presents the survey methodology and focuses on analysing a subset of the results in order to evaluate whether current tools meet the needs of stakeholders and address the challenges of integrating them into design and decision-making processes.

Recent research highlights buildings as significant contributors to greenhouse gas (GHG) emissions, entailing the implementation of legally binding CO2 limits for several countries and a widespread adoption of environmental product declarations (EPDs). While PDF remains the common EPD format, the emergence of the digital ILCD+EPD format introduces start to play a more significant role. The format introduces complexities, posing uncertainties and challenges in effectively managing product data and integrating them into LCA software applications. Despite this, persistent challenges in transparency and comparability underscore the need for robust methodologies to ensure reliable material assessments. Limited literature exists on the applicability and comprehension of the ILCD+EPD format, prompting this study’s exploration, using the Web API from the European umbrella organization, the ECO Platform Portal. By compiling digital EPD files into a standard schema, the study aims to scrutinize the format for enhanced reliability and usability. The study assesses a total of 12,962 datasets from the ECO Platform Portal, revealing discrepancies in compliance and documentation, with adjustments made to ensure accuracy. Notably, 17 datasets were removed due to unknown compliance with EN15804, 2097 datasets were expired, 330 datasets were lacking important information of expiration and functional unit, and 66 datasets were removed due to invalid units unsuitable for building-LCAs This resulted in a total of 10,452 datasets, with 29% allocated to EN15804+A1 and 71% to EN15804+A2. Embracing the ILCD+EPD format enhances EPD effectiveness and improves sustainability practices but requires efforts to address data extraction challenges and inconsistencies.

The environmental performance from the materials used in buildings is pivotal in reducing greenhouse gas (GHG) emissions from the building sector; buildings are in the top three of the world’s most significant contributors of GHG emissions and are responsible for one-fifth of the overall resource consumption. Alongside multiple countries enforcing legal GHG limits and requiring Life Cycle Assessment (LCA) for new buildings, the availability of product-level environmental data, known as Type III Environmental Product Declarations (EPDs) has increased exponentially. EPDs were originally used for Business-to-Business purposes but are now the main data source for building-level LCAs. However, this often comes with a large set of uncertainties, as EPDs are still evolving as a documentation approach, and not always readily applicable in the whole life cycle approach. There are a multitude of complex areas to engage into, this study focuses on how use-stage modules are documented in EPDs, and how varied approaches create further complexity and perils in relation to their use in LCA and regulations, in the sense of, potential leading to high uncertainties and wrongful interpretations. The study aims to address the methodological gaps associated with the use of EPDs as data inputs in legally binding LCA requirements particularly concerning modules B1-5, which constitute the embodied part of the use-stage. The findings reveal a significant margin of error if EPDs are not correctly implemented, underscoring the importance of the Business-to-Business documentation approach.

PurposeThe 71st LCA forum was held on 18 June 2019 in Zurich, Switzerland, to discuss the current status and future plans of environmental benchmarking for buildings in view of the 1.5 °C target stipulated in the Paris Agreement. The Paris Agreement requires a significant reduction in greenhouse gas emissions, in fact net zero by 2050. One of the priority areas is the building stock, as it is an important source of greenhouse gas emissions. COP23, the International Energy Agency (IEA) and an increasing number of countries are extending their consideration from aspects such as energy consumption and emissions from building operation to the manufacture of construction materials and building construction. The event offered an excellent platform to exchange ideas and thoughts on existing and planned environmental benchmarking schemes for buildings.MethodsThe one day event dealt at first with life cycle assessment (LCA) approaches applied in European, Asian, Australasian and American countries to assess the environmental performance of buildings. Within a round robin test, organised within the IEA EBC (Energy in Building and Communities) Annex 72 project, 22 organisations from 21 countries assessed the environmental performance of one identical building, the be2226 office building located in Lustenau, Austria. The materials, the building technologies and the energy consumption were kept constant. This allowed to identify the main differences in LCA data used and LCA methodology applied in the national contexts. In the LCA forum, eight organisations presented the current state or future plans of an environmental benchmarking system in their home country. The systems were characterised in terms of scope, in particular (a) which types of buildings are covered; (b) which life cycle stages are included; (c) which building elements and which operational energy uses are considered; and (d) which environmental impacts are addressed. Furthermore, the default reference service life and the main source of LCA data were specified and the current or planned benchmark values for greenhouse gas emissions of residential buildings were reported.Results and discussionThe round robin test revealed the LCA background data as one major source of difference in assessment results. Methodological and modelling choices were less important except for the Danish assessment, which applies a comparatively long reference study period (80 years for office buildings, 120 years for residential buildings) and considering future changes in the electricity mix towards 100% renewables to describe the operational electricity demand during the lifetime of the building. Most benchmarking systems presented are applied on new and retrofit residential, office and school buildings. Other use types such as shops, restaurants, universities or hospitals are covered only in few or just one country. The greenhouse gas emission benchmark for residential buildings (construction and operation) revealed a significant gap between the current level of the building benchmarks on one hand and the target of net zero CO2-eq emissions derived from the 1.5 °C scenarios of IPCC on the other. An online inquiry carried out among the audience during the event showed a preference for a per capita overall budget of 500 kg CO2-eq per year to derive greenhouse gas emission benchmarks for buildings and that life cycle-based benchmarks for buildings should be legally binding.ConclusionsThe 71st LCA forum on environmental benchmarks for buildings showed that the experts present acknowledge the net zero CO2 emission target derived from the 1.5 °C scenarios. Several countries have expertise and experience in assessing the environmental impacts of buildings. However, the current (mostly voluntary) benchmarking schemes are way too weak to support the building sector in contributing significantly to the required CO2 emission turn off. The outlook given by several speakers showed that the current benchmarks will likely be tightened and oriented on the planetary boundaries and on the scientifically defined CO2 emission budgets rather than on the technical or economic feasibility. Finally, the responsibility of governments for defining environmental requirements and targets was stressed. The event, the exchange of ideas and the discussions helped to nurture and hopefully accelerate the developments in the construction sector of the home countries of the experts and government representatives. These developments will contribute to a society whose environmental impacts remain within the carrying capacity of our planet.

As the built environment accounts for a significant share of global greenhouse gas emissions, achieving whole life cycle net zero carbon buildings has become a pressing objective. Reliable, standardized, and transparent data is critical to support WLC accounting, inform design decisions, and underpin regulatory frameworks. This paper presents the interim findings of collaborative research focusing on the role of GHG emissions databases in supporting WLC assessments of buildings. Building on analysis of data coverage and quality, policy integration and institutional support, the paper delineates a global maturity landscape of existing databases. It also outlines current practices and challenges in data provision and devises a reference framework based on features that highlevel data systems should pursue.