Life Cycle Assessment is a holistic yardstick of the environmental performance of products and services. It measures how much impact a product has both directly and indirectly. An LCA is holistic because it covers all phases of the product's life cycle and it covers all significant environmental impacts.
Like any measuring system, LCA's effectiveness and accuracy depend on the correct use of the tools. There are four phases of the LCA: scoping, inventory development, impact assessment and interpretation. Each of these phases has its challenges, but the pivotal one is scoping. An LCA stands or falls based on its scoping.
When a scoping is done, there are several things that are decided:
The inventory stage of the life cycle assessment is conducted by evaluating the inputs and outputs from unit processes. For example, let's take a generic look at power production, a key input and a major source of environmental impacts for almost all LCA's. In the mining unit process the inventory will include all fuel and electricity consumed. Ideally, it would include information about the changes to the land that are cause by the mining of coal or oil. The inventory would also include information about the emissions to the air and water and any solid waste produced. The same set of inventory information is needed when evaluating transport of fuel, and production of electricity at the power plant, in fact, for all life cycle stages.
For most LCA's all these unit processes are grouped together into a single power generation unit process, including all its upstream impacts. That allows the user to reduce the hundreds or thousands of data points down to just a few dozen, a much easier number to deal with.
Impact Assessment takes inventory data and converts it to indicators for each impact category. A typical list of impact indicators includes:
An impact assessment takes each impact category and models the impacts using an indicator. An indicator does not typically measure actual impacts, but instead provides a numerical result that is believed to correlate well to the actual impacts. Climate change is measured using the global warming potential of the gases released into the atmosphere. It allows one to combine information about the releases of CO2, methane, and nitrous oxide together to get an overall effect on the climate, without modeling the actual impacts on health or ecosystems caused by the droughts, flood and sea level rise, as well as the temperature changes brought about by the changes in the atmosphere.
Other impact categories are calculated in a similar fashion, yielding a numerical indicator for each impact category. The list of impact indicator results is called the ecoprofile. It marks the end of the science of LCA-subsequent steps are based on value judgments.
After calculating indicators, it is possible to combine the different impact indicator results to yield a score of a single number. Or impacts can be compared through normalization-a method that moves the results into units that can be compared more readily. One example of normalization can be found in an ecolabel that we have developed, which reports results as a percentage of the US average for those items. Normalization is useful because it helps users of information put the results into perspective.
Life Cycle Interpretation reviews results for appropriateness, completeness and accuracy and provides guidance to the users of LCA as to how they should use the LCA results. Not all LCA's include this step.
Life Cycle Assessment combines many environmental tools together: systems analysis, input-output analysis, risk assessment and environmental impact assessment. What is unique about the technique is that it reports all results in terms of the functional unit. In this way it directly links the market for goods and services to environmental improvement. It puts the fate of the environment into the hands of purchasers and specifiers of products-like all of you here. LCA gives you a good yardstick to make things get better.