A life-cycle
assessment (LCA, also known as life-cycle analysis, ecobalance,
and cradle-to-grave
analysis)is a technique to assess environmental impacts associated with all the stages
of a product's life from-cradle-to-grave (i.e., from raw material extraction
through materials processing, manufacture, distribution, use, repair and
maintenance, and disposal or recycling). LCA’s can help avoid a narrow outlook
on environmental concerns by:
- Compiling an inventory of relevant energy and material inputs and environmental releases;
- Evaluating the potential impacts associated with identified inputs and releases;
- Interpreting the results to help you make a more informed decision.[2]
Goals and purpose
The
goal of LCA is to compare the full range of environmental effects assignable to
products and services in order 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.
There
are two main types of LCA. Attributional LCAs seek to establish the burdens
associated with the production and use of a product, or with a specific service
or process, at a point in time (typically the recent past). Consequential LCAs
seek to identify the environmental consequences of a decision or a proposed
change in a system under study (oriented to the future), which means that
market and economic implications of a decision may have to be taken into
account. Social LCA is under development[3]
as a different approach to life cycle thinking intended to assess social
implications or potential impacts. Social LCA should be considered as an
approach that is complementary to environmental LCA.
The
procedures of life cycle assessment (LCA) are part of the ISO 14000
environmental management standards: in ISO 14040:2006 and 14044:2006. (ISO
14044 replaced earlier versions of ISO 14041 to ISO 14043.)
Four main phases
According
to the ISO 14040[4]
and 14044[5]
standards, a Life Cycle Assessment is carried out in four distinct phases as
illustrated in the figure shown to the right. The phases are often
interdependent in that the results of one phase will inform how other phases
are completed.
Goal and scope
An LCA
starts with an explicit statement of the goal and scope of the study, which
sets out the context of the study and explains how and to whom the results are
to be communicated. This is a key step and the ISO standards require that the
goal and scope of an LCA be clearly defined and consistent with the intended
application. The goal and scope document therefore includes technical details
that guide subsequent work:
- the functional unit, which defines what precisely is being studied and quantifies the service delivered by the product system, providing a reference to which the inputs and outputs can be related;
- the system boundaries;
- any assumptions and limitations;
- the allocation methods used to partition the environmental load of a process when several products or functions share the same process; and
- the impact categories chosen.
Life cycle inventory
Life
Cycle Inventory (LCI) analysis involves creating an inventory of flows from and
to nature for a product system. Inventory flows include inputs of water,
energy, and raw materials, and releases to air, land, and water. To develop the
inventory, a flow model of the technical system is constructed using data on
inputs and outputs. The flow model is typically illustrated with a flow chart
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. The
input and output data needed for the construction of the model are collected
for all activities within the system boundary, including from the supply chain
(referred to as inputs from the technosphere).
The
data must be related to the functional unit defined in the goal and scope
definition. Data can be presented in tables and some interpretations can be
made already at this stage. The results of the inventory is an LCI which
provides information about all inputs and outputs in the form of elementary
flow to and from the environment from all the unit processes involved in the
study.
Inventory
flows can number in the hundreds depending on the system boundary. For product
LCAs at either the generic (i.e., representative industry averages) or
brand-specific level, that data is typically collected through survey
questionnaires. At an industry level, care has to be taken to ensure that
questionnaires are completed by a representative sample of producers, leaning
toward neither the best nor the worst, and fully representing any regional
differences due to energy use, material sourcing or other factors. The
questionnaires cover the full range of inputs and outputs, typically aiming to
account for 99% of the mass of a product, 99% of the energy used in its
production and any environmentally sensitive flows, even if they fall within
the 1% level of inputs.
One
area where data access is likely to be difficult is flows from the
technosphere. Those completing a questionnaire will be able to specify how much
of a given input they use from supply chain sources, but they will not usually
have access to data concerning inputs and outputs for those production
processes. 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.
Life cycle impact assessment
Inventory
analysis is followed by impact assessment. This phase of LCA is aimed at
evaluating the significance of potential environmental impacts based on the LCI
flow results. Classical life cycle impact assessment (LCIA) consists of the
following mandatory elements:
- selection of impact categories, category indicators, and characterization models;
- the classification stage, where the inventory parameters are sorted and assigned to specific impact categories; and
- impact measurement, where the categorized LCI flows are characterized, using one of many possible LCIA methodologies, into common equivalence units that are then summed to provide an overall impact category total.
In
many LCAs, characterization concludes the LCIA analysis; this is also the last
compulsory stage according to ISO 14044:2006. However, in addition to the above
mandatory LCIA steps, other optional LCIA elements – normalization, grouping,
and weighting – may be conducted depending on the goal and scope of the LCA
study. In normalization, the results of the impact categories from the study
are usually compared with the total impacts in the region of interest, the U.S. for example.
Grouping consists of sorting and possibly ranking the impact categories. During
weighting, the different environmental impacts are weighted relative to each
other so that they can then be summed to get a single number for the total
environmental impact. ISO 14044:2006 generally advises against weighting,
stating that “weighting, shall not be used in LCA studies intended to be used
in comparative assertions intended to be disclosed to the public”. This advice
is often ignored, resulting in comparisons that can reflect a high degree of
subjectivity as a result of weighting.[citation needed]
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 14040:2006, the interpretation should include:
- identification of significant issues based on the results of the LCI and LCIA phases of an LCA;
- evaluation of the study considering completeness, sensitivity and consistency checks; and
- conclusions, limitations and recommendations.
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"!
Interpreting the results of an LCA starts 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.
Reference test
More
specifically, the best alternative is the one that the LCA shows to have the
least cradle-to-grave environmental negative impact on land, sea, and air
resources.[6]
LCA tools and uses
There
are two basic types of LCA tools:
- dedicated software packages intended for practitioners; and
- tools with the LCA in the background intended for people who want LCA-based results without have to actually develop the LCA data and impact measures.
In the
former category, the principal tools are GaBi Software, developed by PE
International, SimaPro, developed by PRé Consultants, Quantis SUITE 2.0,
developed by Quantis International and umberto,
developed by ifu Hamburg GmbH, and web-based solutions include Earthster and LinkCycle.
In the second category, different tools operate at different levels. At the
product level, the U.S. National Institute of Standards and Technology (NIST)
makes its BEES (Building for Environmental and Economic Sustainability) tool
freely available, Solidworks CAD software (Dassault Systèmes) presents LCA-based
environmental information to the user through an add-on called
SustainabilityXpress, and PTC’s Windchill Product Analytics makes LCA results
an integral part of product development systems.[7]
At the whole building design level, different tools are available in different
parts of the world. For example, the ATHENA® Impact Estimator for Buildings is
capable of modeling 95% of the building stock in North America, Envest has been
developed by the Building Research Establishment to meet UK needs, and EcoQuantum is available in the Netherlands.
For the Netherlands,
extensive databases (open access) are available on the so called eco-costs
and carbon footprint of buildings and its components, see winket.
The European Council of Construction
Economists is planning to develop such open source databases for
other European countries as well. At a building assembly level (e.g., exterior
walls) the free ATHENA® EcoCalculator for Assemblies is an example of a tool
that serves North America and the Whole Building Design Guide is an example of
a tool applicable to the UK.
Based
on a survey of LCA practitioners carried out in 2006[8]
LCA is mostly used to support business strategy (18%) and R&D (18%), as
input to product or process design (15%), in education (13%) and for labeling
or product declarations (11%).
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".[9][10]
These third-party certified LCA-based labels provide an increasingly important
basis for assessing the relative environmental merits of competing products.
Third-party certification plays a major role in today's industry. Independent
certification can show a company's dedication to safer and environmental
friendlier products to customers and NGOs.[11]
LCA
also has major roles in environmental impact assessment, integrated waste
management and pollution studies.
Data analysis
A life
cycle analysis is only as valid as its data; therefore, it is
crucial that data used for the completion of a life cycle analysis are accurate
and current. When comparing different life cycle analyses with one another, it
is crucial that equivalent data are available for both products or processes in
question. If one product has a much higher availability of data, it cannot be
justly compared to another product which has less detailed data.[12]
There
are two basic types of LCA data – unit process data and environmental
input-output data (EIO), where the latter is based on national economic
input-output data.[13]
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.
Data
validity is an ongoing concern for life cycle analyses. Due to globalization
and the rapid pace of research and development, new materials
and manufacturing methods are continually being introduced to the market. This
makes it both very important and very difficult to use up-to-date information
when performing an LCA. If an LCA’s conclusions are to be valid, the data must
be recent; however, the data-gathering process takes time. If a product and its
related processes have not undergone significant revisions since the last LCA
data was collected, data validity is not a problem. However, consumer electronics such as cell phones
can be redesigned as often as every 9 to 12 months,[14]
creating a need for ongoing data collection.
The
life cycle considered usually consists of 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 life phase of an airplane or car is during use due to fuel
consumption. One of the most effective ways to increase fuel efficiency is to
decrease vehicle weight, and thus, car and airplane manufacturers can decrease
environmental impact in a significant way by replacing aluminum with lighter
materials such as carbon fiber reinforced fibers. The reduction during the use
phase should be more than enough to balance additional raw material or manufacturing cost.
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 EDPs.[15]
Cradle-to-cradle or open 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.[16]
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.[17]
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 energy conversion efficiency and emissions
impact of marine vessels, aircrafts
and motor vehicle emissions, including their carbon
footprint, and the fuels used in each of these transport modes.[18][19][20]
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).[13]
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.[21]
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.[citation needed]
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.[9]
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[citation needed]. The result was
refuted.[22]
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.[23][24]
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[25]
While incineration produces more greenhouse gas emissions than landfilling, the
waste plants are well-fitted with filters to minimize this negative impact. A
recent study comparing energy consumption and greenhouse gas emissions from
landfilling (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.[26]
Criticism
A
criticism of LCEA is that it attempts to eliminate monetary cost analysis, that
is replace the currency by which economic decisions are made with an energy
currency.[citation needed] It has also
been argued that energy efficiency is only one consideration in deciding which
alternative process to employ, and that it should not be elevated to the only
criterion for determining environmental acceptability; for example, simple
energy analysis does not take into account the renewability of energy flows or
the toxicity of waste products; however the life cycle assessment does help
companies become more familiar with environmental properties and improve their
environmental system.[27]
Incorporating Dynamic LCAs of renewable energy technologies (using
sensitivity analyses to project future improvements in renewable systems and
their share of the power grid) may help mitigate this criticism.[28]
A
problem the energy analysis method cannot resolve is that different energy
forms (heat,
electricity,
chemical
energy etc.) have different quality and value even in natural
sciences, as a consequence of the two main laws of thermodynamics.
A thermodynamic measure of the quality of energy is exergy.
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 by different values.
The
conflict is resolved in one of these ways:
- value difference between energy inputs is ignored,
- a value ratio is arbitrarily assigned (e.g., a joule of electricity is 2.6 times more valuable than a joule of heat or fuel input),
- the analysis is supplemented by economic (monetary) cost analysis,
- exergy instead of energy can be the metric used for the life cycle analysis.[29]
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.[30]
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.[31]
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[32]
found[33]
a lack of consistency in the methods and assumptions used to track carbon
during the product life cycle. 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.
The Agroecology
tool "agroecosystem analysis" offers a
framework to incorporate incommensurable aspects of the life cycle of a
product (such as social impacts, and soil and water implications).[34]
This tool is specifically useful in the analysis of a product made from
agricultural materials such as corn ethanol
or soybean biodiesel
because it can account for an ecology of contexts interacting and changing
through time. This analysis tool should not be used instead of life-cycle
analysis, but rather, in conjunction with life-cycle analysis to produce a
well-rounded assessment.
Dynamic life cycle assessment
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,[35][36][37]
while others have focused on carbon
dioxide and other greenhouse
gases.[38]
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 of energy
technology may emit more carbon
dioxide over its lifetime than it mitigates.
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