Life-cycle assessment

Life-cycle assessment or LCA (also known as life-cycle analysis) is a methodology for assessing environmental impacts associated with all the stages of the life-cycle of a commercial product, process, or service. For instance, in the case of a manufactured product, environmental impacts are assessed from raw material extraction and processing (cradle), through the product's manufacture, distribution and use, to the recycling or final disposal of the materials composing it (grave).
An LCA study involves a thorough inventory of the energy and materials that are required across the industry value chain of the product, process or service, and calculates the corresponding emissions to the environment. LCA thus assesses cumulative potential environmental impacts. The aim is to document and improve the overall environmental profile of the product.
Widely recognized procedures for conducting LCAs are included in the 14000 series of environmental management standards of the International Organisation for Standardisation (ISO), in particular, in ISO 14040 and ISO 14044. ISO 14040 provides the 'principles and framework' of the Standard, while ISO 14044 provides an outline of the 'requirements and guidelines'. Generally, ISO 14040 was written for a managerial audience and ISO 14044 for practitioners. As part of the introductory section of ISO 14040, LCA has been defined as the following:LCA studies the environmental aspects and potential impacts throughout a product's life cycle (i.e. cradle-to-grave) from raw materials acquisition through production, use and disposal. The general categories of environmental impacts needing consideration include resource use, human health, and ecological consequences.Criticisms have been leveled against the LCA approach, both in general and with regard to specific cases (e.g. in the consistency of the methodology, particularly with regard to system boundaries, and the susceptibility of particular LCAs to practitioner bias with regard to the decisions that they seek to inform). Without a formal set of requirements and guidelines, an LCA can be completed based on a practitioner's views and believed methodologies. In turn, an LCA completed by 10 different parties could yield 10 different results. The ISO LCA Standard aims to normalize this; however, the guidelines are not overly restrictive and 10 different answers may still be generated.
Definition, synonyms, goals, and purpose.
Life-cycle assessment (LCA) is sometimes referred to synonymously as life-cycle analysis in the scholarly and agency report literatures. Also, due to the general nature of an LCA study of examining the life cycle impacts from raw material extraction (cradle) through disposal (grave), it is sometimes referred to as "cradle-to-grave analysis".
As stated by the National Risk Management Research Laboratory of the EPA, "LCA is a technique to assess the environmental aspects and potential impacts associated with a product, process, or service, by:
Hence, it is a technique to assess environmental impacts associated with all the stages of a product's life from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling. The results are used to help decision-makers select products or processes that result in the least impact to the environment by considering an entire product system and avoiding sub-optimization that could occur if only a single process were used.
Therefore, the goal of LCA is to compare the full range of environmental effects assignable to products and services by quantifying all inputs and outputs of material flows and assessing how these material flows affect the environment. This information is used to improve processes, support policy and provide a sound basis for informed decisions.
The term "life-cycle" refers to the notion that a fair, holistic assessment requires the assessment of raw-material production, manufacture, distribution, use and disposal including all intervening transportation steps necessary or caused by the product's existence.
Despite attempts to standardize LCA, it is not realistic to assume LCAs will deliver a unique, objective result. Consequently, it should not be considered a single, unique method, but rather a family of methods attempting to quantify results through a different point-of-view. Among these methods are two main types: Attributional LCA and Consequential LCA. Attributional LCAs seek to attribute the burdens associated with the production and use of a product, or with a specific service or process, for an identified temporal period. Consequential LCAs seek to identify the environmental consequences of a decision or a proposed change in a system under study, and thus are oriented to the future and require that market and economic implications must be taken into account. In other words, Attributional LCA "attempts to answer 'how are things (i.e. pollutants, resources, and exchanges among processes) flowing within the chosen temporal window?', while Consequential LCA attempts to answer 'how will flows beyond the immediate system change in response to decisions?"
A third type of LCA, termed "social LCA", is also under development and is a distinct approach to that is intended to assess potential social and socio-economic implications and impacts. Social Life Cycle Assessment (SLCA) is a useful tool for companies to identify and assess potential social impacts along the lifecycle of a product or service on various stakeholders (for example: workers, local communities, consumers). SLCA is framed by the UNEP/SETAC’s Guidelines for social life cycle assessment of products published in 2009 in Quebec. The tool builds on the ISO 26000:2010 Guidelines for Social Responsibility and the Global Reporting Initiative (GRI) Guidelines.
The limitations of LCA to focus solely on the ecological aspects of sustainability, and not the economical or social aspects, distinguishes it from product line analysis (PLA) and similar methods. This limitation was made deliberately to avoid method overload, but recognizes these factors should not be ignored when making product decisions. 
Some widely recognized procedures for LCA are included in the ISO 14000 series of environmental management standards, in particular, ISO 14040 and 14044. Greenhouse gas (GHG) product life cycle assessments can also comply with specifications such as Publicly Available Specification (PAS) 2050 and the GHG Protocol Life Cycle Accounting and Reporting Standard.
Main ISO phases of LCA.
According to standards in the ISO 14040 and 14044, an LCA is carried out in four distinct phases, as illustrated in the figure shown at the above right (at opening of the article). The phases are often interdependent, in that the results of one phase will inform how other phases are completed. Therefore, none of the stages should be considered finalized until the entire study is complete.
Goal and Scope.
The ISO LCA Standard requires a series of parameters to be quantitatively and qualitatively expressed, which are occasionally referred to as study design parameters (SPDs). The two main SPDs for an LCA are the Goal and Scope, both which must be explicitly stated. It is recommended that a study uses the keywords represented in the Standard when documenting these details (e.g. "The goal of the study is...") to make sure there is no confusion and ensure the study is being interpreted for its intended use.
Generally, an LCA study begins with an explicit statement of the goal, which sets out the context of the study and explains how and to whom the results are to be communicated. Per ISO guidelines, the goal must unambiguously state the following items:
The goal should also be defined with the commissioner for the study, and it is recommended a detailed description for why the study is being carried out is acquired from the commissioner.
Following the goal, the scope must be defined by outlining the qualitative and quantitative information included in the study. Unlike the goal, which may only include a few sentences, the scope often requires multiple pages. It it set to describe the detail and depth of the study and demonstrate that the goal can be achieved within the stated limitations. Under the ISO LCA Standard guidelines, the scope of the study should outline the following:
Life Cycle Inventory (LCI).
Life Cycle Inventory (LCI) analysis involves creating an inventory of flows from and to nature (ecosphere) for a product system. It is the process of quantifying raw material and energy requirements, atmospheric emissions, land emissions, water emissions, resource uses, and other releases over the life cycle of a product or process. In other words, it is the aggregation of all elementary flows related to each unit process within a product system.
To develop the inventory, it is often recommended to start with a flow model of the technical system using data on inputs and outputs of the product system. The flow model is typically illustrated with a flow diagram that includes the activities that are going to be assessed in the relevant supply chain and gives a clear picture of the technical system boundaries. Generally, the more detailed and complex the flow diagram, the more accurate the study and results. The input and output data needed for the construction of the model is collected for all activities within the system boundary, including from the supply chain (referred to as inputs from the technosphere).
According to ISO 14044, an LCI should be documented using the following steps:
As referenced in the ISO 14044 standard, the data must be related to the functional unit, as well as the goal and scope. However, since the LCA stages are iterative in nature, the data collection phase my cause the goal or scope to change. Conversely, a change in the goal or scope during the course of the study may cause additional collection of data or removal or previously collected data in the LCI.
The output of an LCI is a compiled inventory of elementary flows from all of the processes in the studied product system(s). The data is typically detailed in charts and requires a structured approach due to its complex nature.
When collecting the data for each process within the system boundary, the ISO LCA standard requires the study to measure or estimate the data in order to quantitatively represent each process in the product system. Ideally, when collecting data, a practitioner should aim to collect data from primary sources (e.g. measuring inputs and outputs of a process on-site or other physical means). Questionnaire are frequently used to collect data on-site and can even be issued to the respective manufacturer or company to complete. Items on the questionnaire to be recorded may include:
Often times, the collection of primary data may be difficult and deemed proprietary or confidential by the owner. An alternative to primary data is secondary data, which is data that comes from LCA databases, literature sources, and other past studies. With secondary sources, it is often you find data that is similar to a process but not exact (e.g. data from a different country, slightly different process, similar but different machine, etc.). As such, it is important to explicitly document the differences in such data. However, secondary data is not always inferior to primary data. For example, referencing another work's data in which the author used very accurate primary data. Along with primary data, secondary data should document the source, reliability, and temporal, geographical, and technological representativeness.
When identifying the inputs and outputs to document for each unit process within the product system of an LCI, a practitioner may come across the instance where a process has multiple input streams or generate multiple output streams. In such case, the practitioner should allocate the flows based on the "Allocation Procedure" outlined in the previous "Goal and Scope" section of this article.
One area where data access is likely to be difficult is flows from the technosphere. The technosphere is more simply defined as the human-made world. Considered by geologists as secondary resources, these resources are in theory 100% recyclable; however, in a practical sense, the primary goal is salvage. For an LCI, these technosphere products (supply chain products) are those that have been produced by human and unfortunately those completing a questionnaire about a process which uses a human-made product as a means to an end will be unable to specify how much of a given input they use. Typically, they will not have access to data concerning inputs and outputs for previous production processes of the product. The entity undertaking the LCA must then turn to secondary sources if it does not already have that data from its own previous studies. National databases or data sets that come with LCA-practitioner tools, or that can be readily accessed, are the usual sources for that information. Care must then be taken to ensure that the secondary data source properly reflects regional or national conditions.
LCI methods include "process-based LCAs", economic input–output LCA (EIOLCA), and hybrid approaches. Process-based LCA is a bottom-up LCI approach the constructs an LCI using knowledge about industrial processes within the life-cycle of a product, and the physical flows connecting them. EIOLCA is a top-down approach to LCI and uses information on elementary flows associated with one unit of economic activity across different sectors. This information is typically pulled from government agency national statistics tracking trade and services between sectors. Hybrid LCA is a combination of process-based LCA and EIOLCA.
Life Cycle Impact Assessment (LCIA).
Life Cycle Inventory analysis is followed by a life-cycle impact assessment (LCIA). This phase of LCA is aimed at evaluating the potential environmental and human health impacts resulting from the elementary flows determined in the LCI. The ISO 14040 and 14044 standards require the following mandatory steps for completing an LCIA:
Mandatory
In many LCAs, characterization concludes the LCIA analysis, as it is the last compulsory stage according to ISO 14044. However, the ISO Standard provides the following optional steps to be taken in addition to the aforementioned mandatory steps:
Optional
Life cycle impacts can also be categorized under the several phases of the development, production, use, and disposal of a product. Broadly speaking, these impacts can be divided into first impacts, use impacts, and end of life impacts. First impacts include extraction of raw materials, manufacturing (conversion of raw materials into a product), transportation of the product to a market or site, construction/installation, and the beginning of the use or occupancy. Use impacts include physical impacts of operating the product or facility (such as energy, water, etc.), and any maintenance, renovation, or repairs that are required to continue to use the product or facility. End of life impacts include demolition and processing of waste or recyclable materials.
Interpretation.
Life-cycle interpretation is a systematic technique to identify, quantify, check, and evaluate information from the results of the life cycle inventory and/or the life cycle impact assessment. The results from the inventory analysis and impact assessment are summarized during the interpretation phase. The outcome of the interpretation phase is a set of conclusions and recommendations for the study. According to ISO 14043, the interpretation should include the following:
A key purpose of performing life cycle interpretation is to determine the level of confidence in the final results and communicate them in a fair, complete, and accurate manner. Interpreting the results of an LCA is not as simple as "3 is better than 2, therefore Alternative A is the best choice". Interpretation begins with understanding the accuracy of the results, and ensuring they meet the goal of the study. This is accomplished by identifying the data elements that contribute significantly to each impact category, evaluating the sensitivity of these significant data elements, assessing the completeness and consistency of the study, and drawing conclusions and recommendations based on a clear understanding of how the LCA was conducted and the results were developed.
Specifically, as voiced by M.A. Curran, the goal of the LCA interpretation phase is to identify the alternative that has the least cradle-to-grave environmental negative impact on land, sea, and air resources.
LCA uses.
At the time of a survey of LCA practitioners in 2006, LCA was being used to support business strategy and R&D (18% each, of total applications surveyed); other uses included LCA as an input to product or process design (15%), its use in education (13%), and its use for labeling or product declarations (11%).
It has been suggested that LCA will be continuously integrated into building practices through the development and implementation of appropriate tools—e.g., the European ENSLIC Building project guidelines—that guide practitioners in applying LCI data methods to planning, design, and construction.
Major corporations all over the world are either undertaking LCA in house or commissioning studies, while governments support the development of national databases to support LCA. Of particular note is the growing use of LCA for ISO Type III labels called Environmental Product Declarations, defined as "quantified environmental data for a product with pre-set categories of parameters based on the ISO 14040 series of standards, but not excluding additional environmental information". Third-party certification plays a major role in today's industry, and third-party certified LCA-based labels provide an increasingly important basis for assessing the relative environmental merits of competing products. In particular, such independent certification is described as indicating a company's dedication to providing clients with safe and environmentally friendly products.
LCA also has major roles in environmental impact assessment, integrated waste management and pollution studies. Important recent studies applying LCA include:
Data analysis.
A life cycle analysis is only as accurate and valid as is its basis set of data. There are two fundamental types of LCA data–unit process data, and environmental input-output (EIO) data. Unit process data are derived from direct surveys of companies or plants producing the product of interest, carried out at a unit process level defined by the system boundaries for the study. EIO data are based on national economic input-output data.
Data validity is an ongoing concern for life cycle analyses. If LCA conclusions are to be valid, data used in the LCA inventory must accurate and valid, and so, with regard to validity, recent. Moreover, when comparing a pair of LCAs for different products, processes, or services, it is crucial that data of "equivalent" quality are available for the pair being compared. If one of the pair, e.g., a product, has a much higher availability of accurate and valid data, it cannot be justly compared to another product which has lower availability of such data.
With regard to the timeliness of data, it has been noted that data validity can be at odds with the time that data-gathering takes. Due to globalization and the pace of research and development, new materials and manufacturing methods are continually being introduced to the market, making it both important and difficult to identify and apply up-to-date information. For instance, in the consumer electronics sector, products such as cell phones may be redesigned as often as every 9 to 12 months, creating a need for rapid, ongoing data collection.
As noted above, the inventory in the LCA usually considers a number of stages including: materials extraction, processing and manufacturing, product use, and product disposal. If the most environmentally harmful of these stages can be determined, then impact on the environment can be efficiently reduced by focusing on making changes for that particular phase. For example, the most energy-intensive stage in the LCA of an aircraft or automobile product is during its use, as a result of fuel consumption during the product lifetime. An effective ways to increase fuel efficiency is to decrease vehicle weight; hence, aircraft and automobile manufacturers can decrease environmental impact through replacement of heavier materials with lighter ones (e.g., aluminium or carbon fiber-reinforced elements), all specifications and other costs being equal.
Data sources used in LCAs are typically large databases. It is not appropriate to compare two options if different data sources have been used to source the data. Common data sources include:
Calculations for impact can then be done by hand, but it is more usual to streamline the process by using software. This can range from a simple spreadsheet, where the user enters the data manually to a fully automated program, where the user is not aware of the source data.
Variants.
Cradle-to-grave.
Cradle-to-grave is the full Life Cycle Assessment from resource extraction ('cradle') to use phase and disposal phase ('grave'). For example, trees produce paper, which can be recycled into low-energy production cellulose (fiberised paper) insulation, then used as an energy-saving device in the ceiling of a home for 40 years, saving 2,000 times the fossil-fuel energy used in its production. After 40 years the cellulose fibers are replaced and the old fibers are disposed of, possibly incinerated. All inputs and outputs are considered for all the phases of the life cycle.
Cradle-to-gate.
Cradle-to-gate is an assessment of a "partial" product life cycle from resource extraction ("cradle") to the factory gate (i.e., before it is transported to the consumer). The use phase and disposal phase of the product are omitted in this case. Cradle-to-gate assessments are sometimes the basis for environmental product declarations (EPD) termed business-to-business EPDs. One of the significant uses of the cradle-to-gate approach compiles the life cycle inventory (LCI) using cradle-to-gate. This allows the LCA to collect all of the impacts leading up to resources being purchased by the facility. They can then add the steps involved in their transport to plant and manufacture process to more easily produce their own cradle-to-gate values for their products.
Cradle-to-cradle or closed loop production.
Cradle-to-cradle is a specific kind of cradle-to-grave assessment, where the end-of-life disposal step for the product is a recycling process. It is a method used to minimize the environmental impact of products by employing sustainable production, operation, and disposal practices and aims to incorporate social responsibility into product development. From the recycling process originate new, identical products (e.g., asphalt pavement from discarded asphalt pavement, glass bottles from collected glass bottles), or different products (e.g., glass wool insulation from collected glass bottles).
Allocation of burden for products in open loop production systems presents considerable challenges for LCA. Various methods, such as the avoided burden approach have been proposed to deal with the issues involved.
Gate-to-gate.
Gate-to-gate is a partial LCA looking at only one value-added process in the entire production chain. Gate-to-gate modules may also later be linked in their appropriate production chain to form a complete cradle-to-gate evaluation.
Well-to-wheel.
Well-to-wheel is the specific LCA used for transport fuels and vehicles. The analysis is often broken down into stages entitled "well-to-station", or "well-to-tank", and "station-to-wheel" or "tank-to-wheel", or "plug-to-wheel". The first stage, which incorporates the feedstock or fuel production and processing and fuel delivery or energy transmission, and is called the "upstream" stage, while the stage that deals with vehicle operation itself is sometimes called the "downstream" stage. The well-to-wheel analysis is commonly used to assess total energy consumption, or the energy conversion efficiency and emissions impact of marine vessels, aircraft and motor vehicles, including their carbon footprint, and the fuels used in each of these transport modes. WtW analysis is useful for reflecting the different efficiencies and emissions of energy technologies and fuels at both the upstream and downstream stages, giving a more complete picture of real emissions.
The well-to-wheel variant has a significant input on a model developed by the Argonne National Laboratory. The Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model was developed to evaluate the impacts of new fuels and vehicle technologies. The model evaluates the impacts of fuel use using a well-to-wheel evaluation while a traditional cradle-to-grave approach is used to determine the impacts from the vehicle itself. The model reports energy use, greenhouse gas emissions, and six additional pollutants: volatile organic compounds (VOCs), carbon monoxide (CO), nitrogen oxide (NOx), particulate matter with size smaller than 10 micrometre (PM10), particulate matter with size smaller than 2.5 micrometre (PM2.5), and sulfur oxides (SOx).
Quantitative values of greenhouse gas emissions calculated with the WTW or with the LCA method can differ, since the LCA is considering more emission sources. In example, while assessing the GHG emissions of a battery electric vehicle in comparison with a conventional internal combustion engine vehicle, the WTW (accounting only the GHG for manufacturing the fuels) finds out that an electric vehicle can save the 50–60% of GHG, while an hybrid LCA-WTW method, considering also the GHG due to the manufacturing and the end of life of the battery gives GHG emission savings 10-13% lower, compared to the WTW.
Economic input–output life cycle assessment.
Economic input–output LCA (EIOLCA) involves use of aggregate sector-level data on how much environmental impact can be attributed to each sector of the economy and how much each sector purchases from other sectors. Such analysis can account for long chains (for example, building an automobile requires energy, but producing energy requires vehicles, and building those vehicles requires energy, etc.), which somewhat alleviates the scoping problem of process LCA; however, EIOLCA relies on sector-level averages that may or may not be representative of the specific subset of the sector relevant to a particular product and therefore is not suitable for evaluating the environmental impacts of products. Additionally the translation of economic quantities into environmental impacts is not validated.
Ecologically based LCA.
While a conventional LCA uses many of the same approaches and strategies as an Eco-LCA, the latter considers a much broader range of ecological impacts. It was designed to provide a guide to wise management of human activities by understanding the direct and indirect impacts on ecological resources and surrounding ecosystems. Developed by Ohio State University Center for resilience, Eco-LCA is a methodology that quantitatively takes into account regulating and supporting services during the life cycle of economic goods and products. In this approach services are categorized in four main groups: supporting, regulating, provisioning and cultural services.
Exergy-based LCA.
Exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. Wall clearly states the relation between exergy analysis and resource accounting. This intuition confirmed by DeWulf and Sciubba lead to Exergo-economic accounting and to methods specifically dedicated to LCA such as Exergetic material input per unit of service (EMIPS). The concept of material input per unit of service (MIPS) is quantified in terms of the second law of thermodynamics, allowing the calculation of both resource input and service output in exergy terms. This exergetic material input per unit of service (EMIPS) has been elaborated for transport technology. The service not only takes into account the total mass to be transported and the total distance, but also the mass per single transport and the delivery time.
Life cycle energy analysis.
Life cycle energy analysis (LCEA) is an approach in which all energy inputs to a product are accounted for, not only direct energy inputs during manufacture, but also all energy inputs needed to produce components, materials and services needed for the manufacturing process.
An earlier term for the approach was "energy analysis". With LCEA, the "total life cycle energy input" is established.
Energy production.
It is recognized that much energy is lost in the production of energy commodities themselves, such as nuclear energy, photovoltaic electricity or high-quality petroleum products. "Net energy content" is the energy content of the product minus energy input used
during extraction and conversion, directly or indirectly. A controversial early result of LCEA claimed that manufacturing solar cells requires more energy than can be recovered in using the solar cell . The result was refuted. Currently, energy payback time of photovoltaic solar panels range from a few months to several years. Another new concept that flows from life cycle assessments is energy cannibalism. Energy cannibalism refers to an effect where rapid growth of an entire energy-intensive industry creates a need for energy that uses (or cannibalizes) the energy of existing power plants. Thus during rapid growth the industry as a whole produces no energy because new energy is used to fuel the embodied energy of future power plants. Work has been undertaken in the UK to determine the life cycle energy (alongside full LCA) impacts of a number of renewable technologies.
Energy recovery.
If materials are incinerated during the disposal process, the energy released during burning can be harnessed and used for electricity production. This provides a low-impact energy source, especially when compared with coal and natural gas While incineration produces more greenhouse gas emissions than landfills, the waste plants are well-fitted with regulated pollution control equipment to minimize this negative impact. A study comparing energy consumption and greenhouse gas emissions from landfills (without energy recovery) against incineration (with energy recovery) found incineration to be superior in all cases except for when landfill gas is recovered for electricity production.
Criticism.
Energy efficiency is arguably only one consideration in deciding which alternative process to employ, and should not be elevated as the only criterion for determining environmental acceptability. For example, a simple energy analysis does not take into account the renewability of energy flows or the toxicity of waste products. Incorporating "dynamic LCAs", e.g., with regard to renewable energy technologies—which use sensitivity analyses to project future improvements in renewable systems and their share of the power grid—may help mitigate this criticism.
In recent years, the literature on life cycle assessment of energy technology has begun to reflect the interactions between the current electrical grid and future energy technology. Some papers have focused on energy life cycle, while others have focused on carbon dioxide (CO2) and other greenhouse gases. The essential critique given by these sources is that when considering energy technology, the growing nature of the power grid must be taken into consideration. If this is not done, a given class energy technology may emit more CO2 over its lifetime than it initially thought it would mitigate, with this most well documented in wind energy's case.
A problem that energy analysis method cannot resolve is that different energy forms—heat, electricity, chemical energy etc.—have different quality and value as a consequence of the two main laws of thermodynamics. According to the first law of thermodynamics, all energy inputs should be accounted with equal weight, whereas by the second law, diverse energy forms should be accounted for using different values. The conflict may be resolved in one of several ways: the value differences between the energy inputs might be ignored, a value ratio may be arbitrarily assigned (e.g., that an input joule of electricity is 2.6-times more valuable than a joule of heat or fuel), the analysis may be supplemented by economic/cost analysis, or exergy, a thermodynamic measure of the quality of energy, may be used as the metric for the LCA (instead of energy).
Critiques.
Life cycle assessment is a powerful tool for analyzing commensurable aspects of quantifiable systems. Not every factor, however, can be reduced to a number and inserted into a model. Rigid system boundaries make accounting for changes in the system difficult. This is sometimes referred to as the boundary critique to systems thinking. The accuracy and availability of data can also contribute to inaccuracy. For instance, data from generic processes may be based on averages, unrepresentative sampling, or outdated results. This is especially the case for the use and end of life phases in the LCA. Additionally, social implications of products are generally lacking in LCAs. Comparative life-cycle analysis is often used to determine a better process or product to use. However, because of aspects like differing system boundaries, different statistical information, different product uses, etc., these studies can easily be swayed in favor of one product or process over another in one study and the opposite in another study based on varying parameters and different available data. There are guidelines to help reduce such conflicts in results but the method still provides a lot of room for the researcher to decide what is important, how the product is typically manufactured, and how it is typically used.
An in-depth review of 13 LCA studies of wood and paper products found a lack of consistency in the methods and assumptions used to track carbon during the product lifecycle. A wide variety of methods and assumptions were used, leading to different and potentially contrary conclusions – particularly with regard to carbon sequestration and methane generation in landfills and with carbon accounting during forest growth and product use.