When the life cycle inventory of American hardwood and competing products has been compiled there will be a huge quantity of data showing, for example: how many tonnes of material are required to make each functional unit; how many litres of oil are burnt to transport each functional unit; and how much pollutant is emitted to the atmosphere during the manufacture of each functional unit. There will also be data showing how much of each functional unit ends up in landfill, or is recycled or burnt at the end of life.
The next stage is to assess the extent to which each of these data items contributes to the various environmental "impact categories" such as land degradation, global warming, acidification, or water pollution. In line with standard LCA procedures, “impact assessment” in the AHEC-commissioned study will involve three steps:
- Classification: all substances will be sorted into classes according to the effect they have on the environment. For example, substances that contribute to the greenhouse effect or that contribute to ozone layer depletion will be divided into two classes. Certain substances will be included in more than one class. For example, NOx is known to be toxic, acidifying and to cause eutrophication.
- Characterization: the substances will be aggregated within each class to produce an effect score. Some substances may have a more intense effect than others. Therefore it will not be sufficient just to add up the quantities of substances involved and it may be necessary to apply weighting factors at this stage.
- Normalisation: this step will be undertaken to gain a better understanding of the relative size of an effect. Each effect calculated for the life cycle of a product will be benchmarked against the known total effect for this class. The AHEC study is expected to use the Eco-indicator method which compares effects with those caused by the average European during a year.