Carnegie Mellon University

A Primer on Life Cycle Assessment

Life cycle assessment (LCA) is a way to investigate, estimate, and evaluate the environmental burdens caused by a material, product, process, or service throughout its life span.  Environmental burdens include the materials and energy resources required to create the product, as well as the wastes and emissions generated during the process.  By examining the entire life cycle, one gets a more complete picture of the environmental impact created and the trade-offs in impact from one period of the life cycle to another.  Results of LCAs can be useful for identifying areas with high environmental impact, and for evaluating and improving product designs. 

Defining a Product Life Cycle

Typically, a product life cycle is defined as a linear progression: 

  • First, raw materials are extracted from the earth.  Some examples are ore, water and oil. 
  • Second, raw materials are processed into finished materials.  For example, bauxite ore is processed into aluminum and oil is processed into plastics. 
  • Third, the materials are manufactured or assembled into a final product.  This stage can often be considered in two parts: first materials are manufactured into parts (for example, an aluminum sheet is manufactured into an automobile body panel).  Then the parts are assembled into a final product (for example, the body panel along with the windows, engine, and many more parts are assembled into a car). 
  • Fourth is the use stage when a consumer has control of the product. 
  • Finally is the waste management stage or end-of-life stage when the product is broken down into component materials for remanufacturing or recycling, or is discarded. 
  • Some add a sixth stage of distribution as the materials and product are transported between stages

During each of these stages, the activities that occur require material and energy resources, and generate wastes and emissions.  Material and energy resources include items such as ores, catalysts, water, coal, natural gas, or electricity.  Wastes include solid wastes (trash) or hazardous wastes.  Emissions include pollutants released to the air, such as sulfur dioxide or carbon dioxide or soot, or to the water, such as sewage or solids.  Life cycle assessment gathers information about the quantity of these resources and wastes at each life cycle stage.  

Why Use Life Cycle Assessment

Life Cycle Assessment gives you a complete picture of a product’s environmental impacts.  It lets you see during which parts of its life cycle the product most negatively impacts the environment.  For example, the life cycle of an automobile consumes much more energy during the use phase (through the gasoline used to operate the vehicle) than during the prior stages to create the materials and parts for the automobile.  Likewise, an LCA helps to identify which impacts are the most significant across the life cycle.  For example, pollutant emissions to water may not be the worst impact at any individual stage of a product life cycle, but when summed across all stages may in fact have the largest impact. 

Information from an LCA can be use:

to differentiate the impacts of two comparable products:  plastic versus paper versus glass cups.  Each requires different raw materials inputs (petroleum, trees, or sand), and different types and amounts of energy to produce.  Likewise, each production process produces different wastes and emissions.  But the plastic or paper cups would likely be thrown away after one or maybe two uses, adding burdens in a landfill.  The glass cup would be reused, but would require water and detergents for cleaning. 

to assess design options for the same product:  automobiles use a wide variety of materials in the various parts.  Steel has typically been used, but plastics and composite materials have been replacing it.  Steel is heavier than the plastics or composites, adding weight to the car that increases the fuel needed to operate the car.  However, steel parts are easily recycled at the end of the vehicle’s life.  (See detailed example to follow.)

to identify where in the life cycle an impact should be targeted for reduction: A package delivery company may be concerned about its carbon dioxide emissions.  One option is to make changes to its delivery vehicles or routing to reduce fuel consumption and the related CO2 emission.  However, examining the life cycle of the service might identify the company’s building electrical usage as a greater contributor to those emissions, and thus reductions could be gained via energy conservation measures in offices or purchasing wind power.   

Examining the entire life cycle provides a broad perspective for an analysis and helps to avoid making decisions that in the end cause greater harm.