The forest and building sector is of major importance in climate change mitigation and therefore construction materials based on forest products are of great interest. While energy efficiency has had a large focus in climate change mitigation in the building sector, the carbon footprint of the construction material is gaining relevance. The carbon footprint of construction materials can vary greatly from one type to another, the building sector is consequently demanding documentation of the carbon footprint of the materials used. Using an environmental product declaration (EPD) is an objective and standardised solution for communicating the environmental impacts of construction products and especially their carbon footprint. Nevertheless, it is challenging to include the features of forest products as pools of carbon dioxide. There is currently a focus on research into methods for the accounting of sequestered atmospheric carbon dioxide and also implementation of these methods into technical standards. This paper reviews the recent research and technical standards in this field to promote a common understanding and to propose requirements for additional information to be included in EPDs of forest-based products. The main findings show the need for reporting the contribution of biogenic carbon to the total on greenhouse gas emissions and removals over the product’s lifecycle. In order to facilitate the implementation of more advanced methods from research, the EPD should also include more detailed information of the wood used, in particular species and origin.
There is an increasing use of carbon footprinting and Environmental Product Declaration (EPD) for communicating the environmental performance of construction products (
The question is: how can carbon storage benefit be measured and reported in the calculation of the carbon footprint of products using LCA? Carbon accounting refers to processes used to measure and track the flows of carbon atoms through technological systems and how these interact with the environment. Methodologies for carbon accounting are assuming greater importance due to concerns regarding the impact of the release of fossil carbon into the atmosphere, primarily as carbon dioxide and methane (
The objective of this paper is to propose requirements for additional information to be included in EPDs of forest-based products (
Which data are needed in emerging research methods for climate change modelling of forest products?
What is required in standards, TR, TS and guidelines for a more complete carbon footprinting of forest products?
What additional information should be included in carbon footprinting of forest products to facilitate the use of emerging methods?
The review includes research methods relevant for dealing with biogenic carbon flows and storage in forest products under the scope of LCA and carbon footprint. We used ISI Web of Knowledge® as well as Google Scholar® for identification of the scientific publications. The literature research was done with the following criteria:
Peer-review papers in English were selected where the biogenic carbon accounting for forest products used in construction was the main objective and including at least the impact category global warming.
Published literature on methodologies needed for accounting of carbon flows of biofuels were excluded, as the focus of the paper is the long-term utilisation of forest products in construction.
Most recent published research methods were considered, starting from 2010.
Publications were selected when methods were described in detail.
Former methods (before 2010) were not considered as they are already integrated into standards, or not used in calculations anymore.
The term technical standards is used as an overall term for international and regional standards, TS, TR, and guidelines which have the purpose of being a formal document giving guidelines and requirements for methods used in carbon footprint of products. This review includes technical standards guidelines that are relevant for LCA, EPD and carbon footprinting with regard to forest products. As EPDs are based on Product Category Rules (PCRs), technical standards focusing on PCRs are also addressed in this review. A PCR is a set of specific rules, requirements and guidelines for developing EPD for one or more product categories (
The section presents the results of the study in three parts: (i) a literature review of emerging methods in research; (ii) a review of technical standards; and (iii) a systematic comparison of the technical standards.
Four recent methods for dealing with biogenic carbon were found in research literature and are presented here.
The methodology developed in
The approach proposed by
The GWPbio methods was first presented by
The data needed for applying the emerging research methods in this review are presented in
There are many technical standards for LCA and carbon footprint available and the one relevant to forest based building materials and biogenic carbon are reviewed. These can be separated into those dealing with only building materials (ISO-21930, EN-15804, CEN/TR-16970, EN-16485) and those which covers all products (PAS-2050, ISO/ TS-14067, PEF). Another distinction is the geographic coverage, where some are international standards (ISO-21930, PAS-2050, ISO/TS-14067), while others are European specific (EN-15804, CEN/TR-16970, EN-16485, PEF) and which would have stronger links to government regulation. These are explained separately in this section and key issues in comparison in the next section.
The
The
The EN-15804:2012+A1:2013 (
As some rules set in EN-15804 are defined in a very general way, the
The
The
In case carbon storage is included in a GHG assessment, the data source and the carbon storage profile shall be recorded. For the calculation of the weighting factor, emissions arising more than one year up to 25 years after formation of the product shall be taken into account. The calculation of delayed emissions represents a simplification of the IPCC approach. However, effects of delayed emissions can only be applied for biogenic carbon, since stored CO2 has to be removed from the atmosphere before the product is created. Moreover, a prerequisite is that the product must be derived from sustainably managed forests. Otherwise, land use change would have occurred and native forests would have been used.
For a delayed single release of GHG emissions within 25 years, a simple equation is given, taking the number of years between formation of the product and the release of the emissions into account. A different equation is provided for GHG emissions arising over several years. In that case, the weighted average impact is provided.
This TS gives guidelines for the quantification of GHG emissions and removals. The TS builds largely on existing ISO standard for LCA (ISO-14040/44) and EPD (
The European Commission is developing an approach similar to EPD called Product Environmental Footprint (PEF) and the goal is a single market for green products. PEF covers all kind of products with a common LCA guidance (
These shall always be reported as total climate change, which is the sum of the three sub-indicators. When “biogenic” and “land use and land transformation” contributes each to more than 5 % of the total score, these shall also be reported.
There are also two options for modelling biogenic carbon. In option 1 all biogenic carbon uptake and releases are modelled. In option 2 a simplified approach can be used, where only biogenic CH4 emissions are modelled.
Each methodological aspect for accounting of biogenic carbon in carbon footprinting and EPDs are here addressed separately and summarised in
During manufacturing of materials containing biogenic carbon, transformation processes often lead to several products and co-products where some kind of allocation method is needed. If economic allocation is applied, the input of biomass raw material will not be the same as the amount of biomass in the final product. Hence, several standards require that, when such allocation is used, economic allocation shall not be applied to biogenic carbon.
The biogenic carbon flows can be accounted as removal of carbon dioxide from the atmosphere during plant growth with negative impacts on the climate impacts of the considered life cycle stage. The term “negative impacts” means that there is a reduction in overall radiative forcing because of the removal of atmospheric carbon dioxide. This is reported as negative carbon dioxide equivalents. If the biogenic carbon is later emitted to the atmosphere, it will have a positive impact on the climate change indicator (an increase in radiative forcing). This is reported as positive carbon dioxide equivalents.
If the emission from biogenic carbon or other carbon takes place a long time into the future, this will have a lower impact on GWP than the same emissions today. This was first considered in the calculations in
Growth of biomass usually affects not only the amount of biogenic carbon in the product harvested, but also in soil, above-ground and below-ground biogenic carbon in forests or agricultural land. These can be defined as part of forest carbon pools as defined by IPCC (2006, cited in
This section compiles the main findings in the results and discuss them in relation to the research questions of the study. First discussing the data needed on emerging methods and then secondly the data required by the technical standards for EPD. Lastly, these findings answers to what should be required in future developments of technical standards (
What is common for most methods is that they include rotation periods and flows from and to the atmosphere at the time the emissions occur. There are however, some differences if only the carbon contained in the harvested stem is included or if other pools like below-ground carbon are included.
The data and information required in technical standards are not consistent and this shows a need for further work on this subject.
The methods of dynamically assessing carbon flows of forests based on information in an EPD for a forest product is dependent on the availability of sufficient information in the EPD additionally to what is currently required. This information however has to be possible to obtain for companies and LCA practitioners with a reasonable effort. It also has to be concise so that it will not take up unnecessary space in an EPD. This information and parameters should be sufficient in order to calculate:
biogenic emissions from biomass within life cycle modules;
rotation period of the biomass;
growth state of the harvested forests on national level.
The
The species of wood or other biomass will contribute to the estimation of the rotation period. For wood, dividing into softwood and hardwoods would not be sufficient as the parameters for instance in
The country or region of origin in combination with the species will enable an estimation of rotation period. In addition, it will also contribute to product specific information necessary to obtain data on the state of national forest inventories. Both species and origin are required to be documented by companies trading timber in the EUTR (
The results of this research highlight the need for more sophisticated modelling of biogenic carbon in LCA, but the different approaches give different results and can be time consuming. Also, there is currently no scientific consensus on which method is the most appropriate for use LCA applied in EPD. The results of the review of technical standards shows that there are difference between those for all products and those covering construction materials. For many products, they are final and the end use is given, in addition to a short lifetime. Construction materials, however, are only intermediate products and the construction is the final product with a long service life. For assessing construction materials based on forest products, the product footprint is often further used as data for construction level assessments. For these reasons modularity in results are important so that adjustments can be made to the specific construction case. In these cases, LCA commissioners might demand that biogenic carbon is assessed with the more sophisticated methods and therefore EPD and PEF should include information facilitating this. In addition to the requirements of
The following abbreviations have been used throughout the manuscript:
CEN: European Committee for Standardisation;
CML-IA: Centre of Environmental Science of Leiden University - Impact assessment method;
DIS: Draft international standard;
EN: European Standard;
EPD: Environmental product declaration;
EUTR: European Union Timber Regulation;
GHG: Greenhouse gas;
GWP: Global warming potential;
ILCD: The International Life cycle Data System;
IPCC: Intergovernmental Panel on Climate Change;
ISO: International Organisation for Standardisation;
LCA: Life cycle assessment;
LCI: Life cycle inventory;
LCIA: Life cycle impact assessment;
PAS: Publicly Available Specification;
PEF: Product environmental footprint;
PEFCR: Product environmental footprint category rules;
PCR: Product category rules;
TR: Technical report;
TS: Technical Specification.
The authors acknowledge COST Action FP1407 in supporting networking activities that resulted in the cooperation behind this publication. Also specifically for supporting a Short Scientific Mission (STSM) with reference code COST-STSM-ECOST-STSM-FP1407-020117-081905 where a large part of this work was performed. Ana Dias acknowledges the project Sustainfor (PTDC/AGR-FOR/1510/2014) funded under the project 3599-PPCDT by FCT (Science and Technology Foundation, Portugal) and by FEDER (European Regional Development Fund). Edwin Zea acknowledges the Chair of Sustainable Construction ETHZ for their support. Callum Hill acknowledges the European Commission Horizon 2020 project ISOBIO (project no. 636835) for financial support.
Data needed for each emerging research method for biogenic carbon accounting. (*): Yes, but reference values are available.
Data needed | DynamicLCA | Approach basedon global carbon cycle | Flexible parametric model for forests | Characterisationfactors for biogenic CO2 emissions with atmospheric decay |
---|---|---|---|---|
Wood species | No | No | Yes | No |
Rotation time | Yes | No | Yes | Yes |
forestry practice (sustainable or not) | Yes | No | No | No |
Biomass annual increment | Yes | Yes | Yes | No |
Biogenic carbon emissions per year over complete life cycle | Yes | Yes | No | Yes |
Biogenic carbon removals per year over complete life cycle | Yes | No | No | Yes |
Basic wood density | Yes | No | Yes | No |
Carbon content of wood | Yes | Yes | Yes | No |
Ratio below-ground/ above-ground biomass | Yes | Yes | Yes* | No |
Biomass conversion and expansion factor | No | No | Yes* | No |
Share of above ground and below-ground slashes | No | Yes | Yes* | No |
Percent woody debris harvested | No | No | Yes* | No |
Summary of methodological aspects related to biogenic carbon accounting in technical standards for carbon footprint of products and EPDs.
Criteria | EN-15804(2012) | ISO/DIS-21930(2015) | EN-15804(2012)+A1:2013 | CEN/TR-16970(2016) | EN-16485(2014) | PEF PilotGuide v2.2February2016 | ISO/TS-14067(2013) | PAS-2050(2011) |
---|---|---|---|---|---|---|---|---|
Instant oxidation allowed | Not specified | Not specified | Not specified | Not specified | Not specified | Yes | Compulsory for emissions less than 10 years | For food |
Considers biogenic carbon in by-product allocation | Yes | Yes | Yes | Not specified | Yes | Not specified | Yes | Not specified |
Consider biogenic carbon flows on GWP | Not directly, but by reference to ILCD method | Yes | Not specified | Yes | Yes | Yes | Yes | Yes |
Modular approach to emissions required | Yes | Yes | Yes | Yes | Yes | No | Yes | Not specified |
Criteria for separate biogenic carbon flows in inventory | Not specified | Yes | Not specified | Yes | Yes | Yes | Yes | Not specified |
Considers sustainable harvest of biomass | Not specified | Yes | Not specified | Yes | Yes | - | Yes, but with land use change | Not specified |
Possible to include effectof delayed emissions on GWP | Not specified | No | Not specified | Not specified | No | No | No | No |
Possible to include effect of delayed emissions separately | Not specified | Yes | Not specified | Not specified | Yes | Yes | Yes | Yes |
Final storage | Not directly, but sets a limit for 100 years | Yes | Not directly, but sets a limit for 100 years | Yes, for landfill | No | Yes | No | Yes |
Land use change | Not specified | Separate, when significant | Not specified | Yes, with impacts on GWP or separate? | Yes, but separate | Yes, but separate | Yes | Yes, on GWP |
Soil organic carbon | Not specified | Not specified | Not specified | Not specified | Yes, but in land use change | Yes, but in land transformation. Soil carbon uptake excluded | Yes, but within land use change. Ongoing research is pointed out | No soil carbon change |
Requires additional information relevant to biogenic carbon | Not specified | Biogenic carbon in materials leaving the product system as technical scenario information | Not specified | Not specified | Apparent density and moisture content of wood, amount of biogenic carbon stored | - | Not specified | Use phase removals and emissions included shall be recorded, carbon storage, land use change |