Life Cycle Assessment: A Systems Approach to Environmental Management and Sustainability

Use this holistic technique to identify and quantify the potential impacts of a product or process throughout its life cycle.

Society is becoming increasingly aware that human activity can have far-reaching impacts. As manufacturing operations have become increasingly diverse, both technically and geographically — from the sourcing of resources, through manufacturing and assembly, to product usage, and finally to disposal — global environmental awareness has become a business imperative. Companies and governments alike have started to look at products and services from cradle to grave.

Examples of a solution to one problem creating another problem are common (1). Compact fluorescent bulbs reduce electricity consumption by 75% but come with a dash of mercury. Biobased fuels reduce greenhouse gas emissions but contribute to air, water, and soil quality impacts in the agricultural stage. Reusable cloth diapers, while made of a renewable, natural material (cotton), require hot water, energy, and detergents for washing.

Twentieth-century environmental strategies seldom considered the entire system, and their solutions were not optimal. Since then, environmental management strategies have evolved and become increasingly broad in scope, moving from end-of-pipe treatment to pollution prevention to sustainable development (Figure 1).

Simultaneously, life cycle assessment (LCA) has become widely recognized as an effective tool for assessing the resource use, environmental burdens, and human health impacts connected with the complete life cycle of products, processes, and activities. This systems approach enables decision-makers to identify environmental hot spots, as well as improve industrial systems without shifting burdens elsewhere. What started as an approach to compare the environmental goodness (greenness) of products has developed into a standardized method for providing a sound scientific basis for environmental sustainability in industry and government.

The product life cycle

Figure 2 depicts the main stages of a product’s life cycle; energy, transportation, and waste management are relevant throughout the life cycle.

Raw material acquisition. This stage includes the removal of raw materials and energy sources from the earth, such as the harvesting of trees or the extraction of crude oil. Land disturbance, as well as transport of raw materials from the point of acquisition to the point of processing, are considered part of this stage.

Manufacturing. The manufacturing stage produces the product from the raw materials and delivers it to consumers. Three substages are involved in this transformation:

• material manufacture. This substage converts raw materials into a form that can be used to fabricate a finished product. For example, several manufacturing activities are required to produce a polyethylene resin from crude oil: The crude oil is refined, ethylene is produced in an olefins unit, and the ethylene is polymerized to produce polyethylene. Transportation between manufacturing activities and to the point of product fabrication should also be accounted for, either as part of materials manufacture or separately.
• manufacturing. In this substage, the manufactured materials are processed to create a product and make it ready to be filled or packaged. Examples of such activities include blow-molding a bottle, forming an aluminum can, or producing a cloth diaper.
• filling, packaging, and distribution. This stage includes all manufacturing processes and transportation required to fill, package, and distribute a finished product. Energy and environmental wastes caused by transporting the product to retail outlets or to the consumer are accounted for in this step of a product’s life cycle.

Use. Consumers are most familiar with this stage — the actual use, reuse, and maintenance of the product. Energy requirements and environmental wastes associated with product storage and consumption are included in this stage.

Recycling and waste management. Energy requirements and environmental wastes associated with product disposal are included in this stage, as well as post-consumer waste-management options, such as recycling, composting, and incineration.

LCA according to the ISO standard

An LCA entails inventorying all the material inputs from the Earth and the outputs to the environment. The results of the life cycle inventory are then run through impact models to calculate potential environmental impact scores, called impact indicators. The LCA model aims to cover all activities related to a product or function, all effects anywhere in the world, and all relevant substances and environmental themes, as well as a long-time horizon.

While simple in concept, the conduct of an LCA can be complicated, mainly due to the large amount of data needed. Fortunately, the increasing availability of LCA databases and software programs makes it easier to conduct an LCA. In addition, the International Organization for Standardization (ISO) established a protocol for performing an LCA study (2, 3). The ISO 14040 series of standards provides the framework for an LCA, which consists of four interrelated phases:

1. Clearly defining the goal and scope of the study (including selecting a functional unit).

2. Compiling a life cycle inventory (LCI) — an inventory of relevant energy and material inputs and environmental releases.

3. Evaluating the potential environmental impacts associated with the identified inputs and releases.

4. Interpreting the results to enable more-informed decision-making.

1. Define the goal and scope of the LCA

An LCA begins with a clearly stated goal. The goal helps to establish the study boundaries and guides the data collection efforts.

The private sector is incorporating LCA in many applications, including various aspects of product design and development, manufacturing, marketing, use and reuse, and disposal and end-of-life management. Common goals for an LCA include:

• establish a baseline of overall environmental impact to identify environmental hot spots
• identify possible opportunities for improvement across the product life cycle
• compare alternative manufacturing processes or supply chains to identify potential trade-offs.
• determine the environmental preferability among alternative product choices
• enable continuous product improvement (often with a concrete target, e.g., the new product must be x% less impactful than its predecessor while providing comparable performance).

Most government agencies and other public sector entities lag behind the private sector in embracing LCA as a tool to support decision-making. LCA results can be useful in setting public policy at multiple levels, and can establish a culture based on life cycle thinking that helps set the course toward a greener, more environmentally sustainable economy. Common goals for a public sector LCA include:

• inform government policies and the prioritizing of their programs and activities
• establish consistent policies across consumers, producers, suppliers, retailers, and waste managers
• establish consistent policies and policy goals, such as harmonizing regulations, voluntary agreements, taxes, and subsidies
• introduce policies that appropriately support post-consumer recycling systems.

The goal setting and scope definition phase also requires the selection of the functional unit, a unique feature of LCA that sets it apart from other environmental assessment approaches. The functional unit is defined by the service that the system being studied provides and is further shaped by the study’s goal.

For example, a study of compact fluorescent lightbulbs (CFLs) might define the system functionality as the production, use, and disposal of a single bulb, or it could refer to a fixed quantity, such as 1,000 bulbs. Although the results of a study defined in this way may be useful for identifying environmental hot spots, a different function is needed to compare CFLs to a competing product, such as incandescent bulbs. A more-appropriate function for that type of study would be performance-based, e.g., the amount of light needed to illuminate a 15-m² room with 1,000 lumen for one hour.

It is important to properly set the scale of the functional unit. If it is set too small, the LCA might attribute to it an inappropriately small (often nearly infinitesimal) share of the total input to or impact of the system (4). For example, the amount of mercury used to make a single CFL is relatively small, so the impact associated with making one, or even a thousand, CFLs may not be significant. On the other hand, an LCA with a functional unit of, say, ten million light bulbs would identify a much larger impact.

2. Compile a life cycle inventory

The life cycle inventory is the compilation of data about the various unit processes within the system under study. Typically, a flow diagram, such as the one for a concrete product shown in Figure 3(5), depicts the processes that make up the system. Flow diagrams are, in fact, huge webs of interconnected unit processes that fulfill the system function and support the functional unit, as defined by the study goal. In today’s era of digital databases, an LCA study can easily be comprised of several hundred unit processes.

The ISO standard provides a general framework for conducting an LCA, but it is open to much interpretation by the practitioner. LCAs can produce different results even if the same product seems to be the focus of the study. Numerous factors might account for such differences, including different goal statements, different functional units, different boundaries, and different assumptions used to model the data (e.g., the use of cut-off rules, co-product allocation, assigning credit for avoided burden, and applying consequential LCA). The key is to keep assumptions to a minimum and explicitly report the assumptions and values on which the LCA is based. Readers of the study can then recognize the judgments and decide whether to accept, qualify, or reject them and the study as a whole.

Cut-off rules. Ideally, a life cycle study would account for all life cycle steps and...