Life cycle assessment (LCA), also called life cycle analysis, is a method used to study the environmental effects of a product, process, or service throughout its entire life. For example, when examining a manufactured product, environmental impacts are studied from the time raw materials are extracted and processed (the beginning), through the product's creation, transportation, and use, to the recycling or final disposal of its materials (the end).

An LCA study carefully lists the energy and materials needed at every stage of a product’s supply chain and value chain. It also calculates the emissions released into the environment. This method helps measure the total environmental effects of a product. The goal is to record and improve the product’s overall environmental impact by providing a complete reference for comparing carbon footprints.

The LCA method follows the ISO 14040 (2006) and ISO 14044 (2006) standards. These standards are part of the ISO 14000 series, which includes widely accepted guidelines for environmental management. ISO 14040 explains the "principles and framework" of LCA, while ISO 14044 outlines the "requirements and guidelines." ISO 14040 is written for managers, and ISO 14044 is designed for people who carry out LCAs. According to ISO 14040, LCA is defined as a process that evaluates environmental impacts across all stages of a product’s life.

Some people have pointed out challenges with the LCA approach. These include issues like inconsistent methods, difficulty in performing LCAs, high costs, concerns about revealing private information, and confusion about what parts of a system should be studied. If the proper LCA method is not followed, results may depend on the opinions of the person conducting the study or the goals of the organization funding it. This can lead to different results when multiple groups perform the same LCA. The ISO LCA Standard aims to make results more consistent, but the guidelines are not strict enough to ensure identical outcomes every time.

Definition, synonyms, goals, and purpose

Life cycle assessment (LCA) is sometimes called life cycle analysis in reports and studies by scholars and agencies. Because an LCA looks at the environmental effects of a product from the start (cradle) to the end (grave), it is also called "cradle-to-grave analysis."

According to the National Risk Management Research Laboratory of the EPA, LCA is a method used to study the environmental effects of a product, process, or service. This method involves:
• Making a list of all energy, materials, and environmental releases involved
• Evaluating the environmental effects of these inputs and releases
• Interpreting the results to help people make better decisions

LCA studies all stages of a product’s life, including getting raw materials, processing materials, making the product, distributing it, using it, repairing or maintaining it, and finally disposing of it or recycling it. The results help decision-makers choose products or processes that harm the environment the least by looking at the whole system instead of just one part.

The goal of LCA is to compare the environmental effects of products and services by measuring all materials used and how they affect the environment. This information helps improve processes, support policies, and make better decisions.

The term "life cycle" means that a fair and complete assessment must include all steps, such as making raw materials, manufacturing, distributing, using, and disposing of a product, along with any transportation needed.

Even though there are rules to standardize LCA, results from different LCAs can often be different. This means it is not always possible to get the same answer or a completely objective result. Instead, LCA is a group of methods that try to measure results from different viewpoints. Two main types of LCA are Attributional LCA and Consequential LCA.

Attributional LCA looks at the environmental effects of a product or process during a specific time period. Consequential LCA looks at the future effects of a decision or change in a system and considers how markets and economics might be affected. In short, Attributional LCA asks, "How are materials and pollution moving during a certain time?" while Consequential LCA asks, "How will changes in the system affect the environment in the future?"

A third type of LCA, called "social LCA," is still being developed. It focuses on the social and economic effects of a product or service on people, such as workers, communities, and customers. Social LCA follows guidelines from UNEP/SETAC, ISO 26000, and the Global Reporting Initiative (GRI).

LCA focuses only on environmental effects, not economic or social ones, which makes it different from methods like product line analysis (PLA). This focus was chosen to keep the method simple, but it is important to consider other factors when making product decisions.

Some common LCA methods are found in the ISO 14000 series of environmental standards, especially ISO 14040 and 14044. Greenhouse gas (GHG) life cycle assessments can also follow rules like Publicly Available Specification (PAS) 2050 and the GHG Protocol Life Cycle Accounting and Reporting Standard.

Main ISO phases of LCA

According to the ISO 14040 and 14044 standards, a Life Cycle Assessment (LCA) is completed in four steps. These steps are connected, meaning the results from one step help guide how the other steps are done. None of the steps should be considered finished until the entire study is complete.

An LCA study starts with defining the goal and scope. This includes details about the product’s purpose, the functional unit (a clear measure of what is being studied), the product system and its boundaries, assumptions, data categories, allocation methods, and the review process. The ISO LCA Standard requires specific parameters to be described both quantitatively and qualitatively, called study design parameters (SPDs). The two main SPDs are the goal and scope, which must be clearly stated.

The goal of the study should be clearly explained. It should describe the study’s purpose, the reasons for conducting it, the audience, and whether the results will be used in public comparisons. The goal must be agreed upon with the person or group commissioning the study, and a detailed explanation of why the study is being done should be recorded.

The scope defines the study’s details. Unlike the goal, which is short, the scope often requires many pages. It describes how detailed the study will be and ensures the goal can be met within the study’s limits. The scope must include the following:

• Product system: A group of processes (activities that change inputs into outputs) needed to complete a specific task and included in the study’s boundaries. It represents all processes in a product’s life cycle.
• Functional unit: A precise measure of what is being studied, used to compare different products or services. It should be quantifiable, include units, and answer questions like: What? How much? For how long? Where? How well?
• Reference flow: The amount of product or energy needed to achieve the functional unit. This may vary between products or systems.
• System boundary: The limits of which processes are included in the study, including whether co-products (products made alongside the main product) are accounted for.
• Assumptions and limitations: Any decisions or assumptions made during the study that could affect results. These must be clearly documented to avoid misunderstandings.
• Data quality requirements: Details about the types of data used, including time, location, technology, and data accuracy.
• Allocation procedure: A method to divide inputs and outputs for processes that produce multiple products. ISO 14044 outlines steps to handle this, such as separating processes or expanding the system to avoid conflicts.
• Impact assessment: A list of environmental impact categories (e.g., global warming, water use) and the methods used to calculate them.
• Data documentation: A clear record of all inputs and outputs used in the study, explaining why specific data was chosen.

Life Cycle Inventory (LCI) analysis lists all materials, energy, and waste flows related to a product’s life cycle. It involves quantifying resources used, emissions released, and other environmental impacts. To create the inventory, a flow model of the technical system is often used, showing inputs and outputs in a supply chain. This helps define the study’s boundaries and processes.

LCA uses

LCA was mainly used to compare products, showing useful information about their environmental effects and how they compare to other choices. Over time, it was also used for marketing, designing products, creating new products, planning strategies, teaching consumers, labeling products for environmental benefits, and helping governments make policies.

ISO has three types of environmental labels:

• Type I labels require a group not connected to the product to check if it meets certain rules, as described in ISO 14024.
• Type II labels are claims made by the product’s company about its environmental benefits, as described in ISO 14021.
• Type III labels, also called environmental product declarations (EPDs), use LCA to report how a product affects the environment, following ISO standards 14040 and 14044.

EPDs help show information clearly, which is now required by many policies and rules worldwide. They are used in construction and buildings to help experts study the full life of a building more easily, because they provide details about the environmental effects of individual products.

Data analysis

A life cycle analysis is only as accurate and valid as the data it uses. There are two main types of LCA data: unit process data and environmental input-output (EIO) data. Unit process data collects information about a single industrial activity and its product(s), including resources used from the environment and other industries, as well as emissions created throughout the product’s life. EIO data are based on national economic input-output data.

In 2001, ISO published a technical standard for documenting data, describing the format for life cycle inventory data (ISO 14048). The format includes three areas: process details, modeling and validation methods, and administrative information.

When comparing LCAs, the data used in each analysis should be of similar quality. Comparisons cannot be fair if one product has much more accurate and valid data than another.

Sensitivity analysis in LCA helps identify which factors most affect the results and can reveal sources of uncertainty. Parametric LCA workflows use models where certain inputs are treated as adjustable values instead of fixed numbers. These values can change systematically during repeated calculations. For example, some parameters are discrete, like choosing a specific dataset, while others are continuous, such as process temperature, production yield, or electricity use. Connecting these parameters to a computational model allows many scenarios to be tested efficiently within the same model structure. This setup supports systematic sensitivity analysis and uncertainty analysis, such as through Monte Carlo simulation.

Data used in LCAs often come from large databases. Common sources include:

As mentioned earlier, an LCA typically considers several stages, such as material extraction, processing and manufacturing, product use, and disposal. When an LCA covers all stages of a product, the stage with the greatest environmental impact can be identified and addressed. For example, an LCA of a woolen garment examined its environmental effects during production, use, and disposal. It found that fossil fuel energy use was mainly caused by wool processing, and greenhouse gas emissions were mainly caused by wool production. However, the most significant factor was how often the garment was worn and how long it lasted, showing that consumer behavior has the biggest effect on the product’s overall environmental impact.

Variants

Cradle-to-grave is a full life cycle assessment that includes all stages of a product's life, starting with resource extraction (called the "cradle"), followed by manufacturing, use, maintenance, and ending with disposal (called the "grave"). For example, trees are used to make paper, which can be recycled into a type of insulation made from fibers. This insulation is used in a home's ceiling for 40 years and saves 2,000 times the energy used to make it. After 40 years, the old insulation is replaced and disposed of, possibly by burning. Every input and output is considered for all stages of the product's life.

Cradle-to-gate is a partial life cycle assessment that includes resource extraction and manufacturing but stops at the factory gate (before the product is sent to the consumer). It does not include the use or disposal stages. Cradle-to-gate assessments are sometimes used to create environmental product declarations (EPDs) for businesses. These assessments help collect data about the resources used up to the point of purchase, allowing companies to add transportation and manufacturing steps to calculate their own cradle-to-gate values for their products.

Cradle-to-cradle is a type of cradle-to-grave assessment where the end-of-life stage involves recycling the product. This method aims to reduce environmental harm by using sustainable production, use, and disposal practices. It also includes social responsibility in product development. Recycled materials can be used to make new products of the same type (e.g., old asphalt pavement made into new asphalt pavement) or different products (e.g., glass bottles made into insulation).

Tracking environmental impacts for products in open-loop systems is challenging for life cycle assessments. Methods like the "avoided burden approach" have been suggested to address these challenges.

Gate-to-gate is a partial life cycle assessment that focuses only on one step in the production process. These steps can later be connected to form a complete cradle-to-gate evaluation.

Well-to-wheel (WtW) is a specific type of life cycle assessment used for transport fuels and vehicles. It is divided into stages: "well-to-station" or "well-to-tank" (fuel production and delivery) and "station-to-wheel" or "tank-to-wheel" (vehicle operation). This method is used to evaluate energy use, efficiency, and emissions from marine vessels, aircraft, and motor vehicles, including their carbon footprints and the fuels they use. WtW analysis helps compare the efficiency and emissions of different energy technologies and fuels at both the fuel production and vehicle operation stages.

The WtW method is based on a model developed by Argonne National Laboratory called GREET. This model evaluates the impacts of new fuels and vehicle technologies by using a well-to-wheel approach for fuel use and a traditional cradle-to-grave method for vehicle impacts. It reports energy use, greenhouse gas emissions, and six other pollutants: volatile organic compounds (VOCs), carbon monoxide (CO), nitrogen oxide (NOx), particulate matter (PM10 and PM2.5), and sulfur oxides (SOx).

Greenhouse gas emissions calculated using well-to-wheel (WtW) or life cycle assessment (LCA) methods can differ because LCA considers more sources of emissions. For example, comparing a battery electric vehicle to a traditional gasoline car, WtW estimates that the electric vehicle saves about 50–60% in greenhouse gas emissions. However, using a combined LCA-WtW method, which includes emissions from battery manufacturing and disposal, the savings are 10–13% lower.

Economic input–output LCA (EIOLCA) uses data about how much environmental impact each economic sector causes and how much each sector buys from others. This method can track long chains of production (e.g., building a car requires energy, but producing energy requires vehicles, and so on). While this helps simplify some challenges in traditional LCA methods, EIOLCA uses averages for entire sectors, which may not reflect the specific impacts of a particular product. It is not suitable for evaluating the environmental impacts of individual products. Additionally, converting economic data into environmental impacts is not fully validated.

A traditional LCA uses similar methods to Eco-LCA, but Eco-LCA considers a broader range of ecological effects. Developed by Ohio State University’s Center for Resilience, Eco-LCA evaluates the direct and indirect impacts of human activities on ecosystems and natural resources. It includes four types of ecosystem services: supporting, regulating, provisioning, and cultural services.

Exergy is the maximum useful work a system can produce when it reaches equilibrium with a heat reservoir. Exergy analysis connects to resource accounting and has led to methods like Exergetic Material Input per Unit of Service (EMIPS). This approach uses the second law of thermodynamics to calculate both resource input and service output in terms of exergy. EMIPS has been applied to transport technology, considering factors like total mass transported, distance, mass per transport, and delivery time.

Life cycle energy analysis

Life cycle energy analysis (LCEA) is a method that tracks all energy used to create a product, including not only energy directly used during manufacturing but also energy needed to produce materials, parts, and services required for manufacturing. LCEA helps calculate the total energy used throughout a product’s entire life.

It is known that producing energy sources, such as nuclear power, solar electricity, or refined petroleum, requires significant energy. Net energy content is the total energy in a product after subtracting the energy used to extract and process it. Early LCEA studies suggested that making solar cells used more energy than they could recover. However, solar cell efficiency improved over time, and today, solar panels typically recover their energy use in a few months to several years. Recycling solar panels could reduce this time to about one month. Another concept from LCEA is energy cannibalism, which occurs when rapid growth in an energy-heavy industry uses so much energy that it cancels out the energy produced by existing power plants. During such growth, the industry may not generate net energy because new energy is used to build future power plants. Studies in the UK have examined the life cycle energy impacts of various renewable technologies.

When materials are burned during disposal, the energy released can be used to generate electricity. This method is less harmful to the environment than using coal or natural gas. Although incineration produces more greenhouse gases than landfills, pollution control systems in waste plants reduce these emissions. A study found that incineration with energy recovery is better than landfills without energy recovery in most cases, except when landfill gas is used for electricity.

Energy efficiency is one factor in choosing an energy process, but it should not be the only consideration. For example, energy analysis does not account for whether energy sources are renewable or how harmful waste products are. Using "dynamic LCAs," which consider future improvements in renewable energy systems, may help address these issues.

Recent research on energy technology life cycle assessments has highlighted how current and future energy systems interact. Some studies focus on energy use, while others examine carbon dioxide and other greenhouse gas emissions. A key point is that the growing size of the electrical grid must be considered when evaluating energy technologies. If not, a technology may produce more carbon emissions over its lifetime than expected, as seen in some wind energy studies.

A challenge in energy analysis is that different energy forms, such as heat, electricity, and chemical energy, are not easily compared because they have different qualities and values. This is because the first law of thermodynamics measures energy changes, while the second law measures energy loss. Alternatives like cost analysis or exergy may be used instead of energy as a metric for life cycle assessments.

LCA dataset creation

There are organized sets of data used for life cycle assessments (LCAs).

A 2022 dataset included standardized calculations of environmental effects for more than 57,000 food items sold in supermarkets. This information could help consumers or policymakers make decisions. There is also at least one database where people can share data about LCAs for food products.

Some datasets include options, activities, or methods instead of products. For example, one dataset evaluates ways to manage PET bottle waste in Bauru, Brazil. Other datasets focus on buildings, which are complex products. A 2014 study compared these types of datasets.

Efforts are being made to create, combine, improve, and maintain these datasets or LCAs. Examples include:

• The LCA Digital Commons Project by the U.S. National Agricultural Library aims to create a database and tools to provide data for LCAs of food, biofuels, and other bioproducts.
• The Global LCA Data Access network (GLAD), part of the UN's Life Cycle Initiative, is a platform that helps users search, convert, and download datasets from various LCA providers.
• The BONSAI project seeks to create a shared resource where the community can help generate, check, and manage data for "product footprinting." Its first goal is to create an open dataset and open-source tools to support LCA calculations. Product footprinting refers to providing reliable, unbiased information about the sustainability of products.

Datasets that are not accurate or have missing information can be temporarily or permanently improved using methods such as selecting datasets that better represent the missing data or using machine learning.

Integration in systems and systems theory

Life cycle assessments can be used regularly as part of systems, as information for future economic and social plans, or in broader discussions (like general situations).

For example, a study looked at the environmental benefits of using microbial protein in a future economic and social plan. It found that replacing 20% of per-person beef with microbial protein by 2050 could reduce deforestation by 56% and help reduce climate change effects.

Life cycle assessments, including those that examine products or technologies, can also be used to analyze opportunities, challenges, and ways to change or control how things are made or used.

The life cycle approach also helps consider how long rare goods and services last in the economy. For example, as of 2022, many rare metals used in technology are not used for long periods. This information can be combined with traditional life cycle assessments to help analyze material and labor costs over time, or to design more sustainable systems. One study from 2013 said that in life cycle assessments, resource availability is studied using models based on how quickly resources are used up or how much energy is available.

In general, different types of life cycle assessments (or creating them) can be used in many ways to help society make decisions. This is especially important because financial markets in the economy usually do not consider the long-term effects of life cycle choices or the problems they may cause in the future or present—these are called "externalities" to the current economy.

Critiques

Life cycle assessment is a method used to study different parts of systems that can be measured. However, not all parts of a system can be turned into numbers for use in models. Setting strict limits on what is included in a study can make it hard to account for changes in the system. This issue is sometimes called the boundary critique in systems thinking. The quality and availability of data can also affect how accurate a study is. For example, data from general processes might be based on averages, samples that do not represent the whole, or old results. This is especially true for the use and end-of-life stages in life cycle assessments. Social effects of products are often not included in these studies. Comparative life cycle analysis is used to compare products or processes and find the better option. However, differences in how systems are defined, the data used, and how products are used can lead to different results in different studies. Guidelines exist to help reduce these differences, but researchers still have choices about what is important, how products are usually made, and how they are used.

A detailed review of 13 life cycle studies on wood and paper products found that the methods and assumptions used to track carbon during the product’s life varied widely. This led to different and sometimes conflicting results, especially when studying how carbon is stored in forests, how methane is created in landfills, and how carbon is counted during product use.

Recent research has raised concerns about the reliability of Life Cycle Inventory (LCI) data for composite materials. Problems include incomplete data, lack of transparency, and differences in how methods are applied, which can affect the results of life cycle assessments. A comparison of 20 databases showed large differences in LCI values for the same materials across different sources. Other studies have shown how much numbers can vary between databases. More recently, studies using Benford’s law on LCI data found more inconsistencies, with differences seen not only in different regions but also within specific environmental areas.

The accuracy of life cycle assessments can also vary because some data may not be included, especially in early studies. For example, studies that ignore regional information about emissions might underestimate the environmental impact of a product’s life cycle.