life cycle assessment heading

Higher and foundation tier

A life cycle assessment (LCA) is a way to try and measure the total impact on the environment that a manufactured product has. A life cycle assessment should look at every stage from obtaining the raw materials needed to manufacture the product, to the environmental impact of its manufacture and use and finally the impact on the environment when the product reaches the end of its useful life and is disposed of. A properly worked LCA should enable you to decide for example whether it is worthwhile recycling a product or simply manufacturing a new replacement product if this has a smaller environmental impact.

The life cycle assessment usually has 4 stages:

  1. Obtaining the raw materials
  2. Manufacturing the product
  3. Using the product
  4. End of product life- disposal
At each stage of the cycle an assessment needs to be made of all the activities that take place and their environmental impact. This is outlined in the diagram below:

stages in a life cycle assessment

A life cycle assessment

Below is a LCA comapring the use of plastic carrier bags against using paper bags. By comparing the LCAs for paper and plastic bags it should be possible to make an informed decision as to which bag will cause less environmental damage throughout its life and whether it is better to recycle or make new replacement bags.

life cycle assessment stage plastic carrier bag paper carrier bag
stage 1 - raw materials plastic bags are made from monomers obtained from crude oil. Crude oil a limited finite resource which requires large amounts of energy to extract it from under the sea or from land. The crude oil needs to be further refined at the oil refinery. Further chemical processes, namely cracking and polymerisation are then required to make the plastic bag. Each step uses large amounts of energy and will produce large amounts of carbon dioxide, a greenhouse gas. paper bags are made from wood pulp or from recycled paper products. Using recycled products will have less of an environmetal impact than cutting down trees to make wood pulp. Also saves land if recycled paper products are used.
stage 2- manufacturing the product plastic bags can be made very cheaply and in large quantities very quickly. Processes will require specialised machinery. Little waste product produced. paper bags made from wood pulp will require large amounts of energy to process the pulp. Lots of waste material will be produced. Smaller quantities of bags can be produced in any given time period compared to plastic bags.
stage 3 - use Can are reusable and can last many months. Paper bags are not as strong as plastic bags, especially if they get wet. Can realistically only be used a few times.
stage 4- disposal Unlikely to be recycled by the vast majority of people. Large amounts end up in landfill where they take decades or longer to decompose and rot down. easy to recycle paper bags. Paper bags will decompose quickly in the environment
From this LCA it is not clear whwether paper or plastic bags have the largest negative environmental impact. More data would be needed on the energy quantities needed to extract the crude oil from the ground and transport it to the refinery. Similarly more detailed figures are needed for the energy required to fell and transport the trees to the paper mill and the impact on the environment of felling large numbers of trees. More data would also be needed on the percentage of reuse for each type of bag and how many people are reusing the bags as opposed to treating them as single use items.

Problems with LCAs

The amount of energy and natural resources used over the lifetime of a product is usually relative easy to calculate. Scientists can calculate the amount of energy used in manufacturing, transporting and extracting a material. However it is not so easy to measure the environmetal impacts of certain products or pollutants easily. Some of these measurements require judgements to be made by people and these judgement are not always reliable and are open to bias. It is possible that the people making these judgements may be trying to push their own ideas and agenda. Different people can make different judgements about the same thing simply because they have differnet agendas to persue and their judgements make not be entirely accurate and made with all the relevant facts taken into account. Therfore it is important to know who has completed the LCA before you make any of your own decisons and judgements.