The environment is a broad concept. You’ve probably heard of CO2, or carbon dioxide. But there are many more emissions, some less known, but not with any less impact on the environment. Nitrogen is for example one of them, causing a lot of problems for Dutch society.
When conducting a life cycle assessment (LCA), a lot of different effects on the environment are taken into account. These different effects are grouped into what we call 'impact categories'. The one widely known is global warming, or climate change. This impact category groups all greenhouse gases (like carbon dioxide, methane and nitrous oxide) into one category that contributes to climate change. The unit used to express them is CO2 equivalents.
However, there’s also this thing called the ozone layer, there’s the health of our soils, and the depletion of resources for example. These are all separate impact categories.
Find out more on the other impact categories and how to deal with them. For a recap on LCA, please go here.
What are impact categories
Impact categories are sometimes also called indicators. They are certain emissions, grouped into one category. However, ‘indicator’ is just a generic word that refers to a signal. Accordingly, greenhouse gas emissions are indicators of global warming. Thus, each impact category has its own defined indicators.
Each impact category represents a specific environmental theme, or place in the ecosystem. In the life cycle impact assessment (LCIA) phase, the life cycle inventory data is translated into their effect on various environmental themes. Impact assessment is about being able to take into account the actual effects on humans, ecosystems, and resources. Whereas the inventory phase only tracks the quantities like tons of emissions or litres of fuel.
For example: in order to produce a certain product, you need natural gas. The amount of m3 natural gas used comes from your inventory (LCI). By burning natural gas, CO2 is released, among other emissions. In the LCIA phase, the climate impact of the CO2 emissions impacting global warming, is expressed and calculated.
Different LCIA methods
There are different impact assessment methods, leading to different impact categories. Some of the ones that are widely known are for example CML-IA (basis for EN15804), Product Environmental Footprint (PEF) or ReCiPe.
But then, some impact categories - covered in multiple impact assessment methods - are based on the same source. This is for example the case with Climate change or Global Warming Potential. In most LCIA methods, this is based on research of IPCC.
The table below shows all impact categories according to the Environmental Footprint (EF) method.
Midpoints and endpoints
LCIA can be performed at different levels. Midpoint indicators - like the ones in the table - are in the middle of the cause-effect chain. When the impact assessment is based on midpoint impact indicators, the classification gathers the inventory results into groups of substance flows that have the ability to contribute to the same environmental effect. Midpoints describe the impact on the various environmental themes separately, such as climate, ozone depletion etc.
The damage from all midpoints combined can then be calculated into endpoints, also called areas of protection. Here midpoints are combined into one measure of damage, often for three general areas: human health damage, ecosystem damage (biodiversity loss) and resource depletion. These endpoints are easier to understand and communicate, but are less precise.
Not every impact assessment method has endpoint characteristics available. Of the three mentioned in this article, only ReCiPe has them.
Who's your audience?
ISO 14044 - the standard that provides the guidelines for LCAs - gives some requirements and additional recommendations when it comes to selecting the right impact categories. It says for example that the choice of impact categories needs to assure that they:
• Are not redundant and do not lead to double counting
• Do not disguise significant impacts
• Are complete
• Allow traceability
Furthermore, ISO states some additional mandatory criteria. Firstly, the list of impact categories needs to be consistent with the goal and scope of the study. When you for example perform a complete environmental assessment, you cannot focus on a single impact category.
Secondly, the selected impact categories need to be comprehensive when it comes to the environmental issues related to the product system under study. So potential environmental issues from your product need to be reflected by an impact category.
Thirdly, the selection needs to be well documented, with all information and sources being referenced. This is tackled by writing an LCA report, according to ISO 14044 and ISO 14040.
Of course, there are external factors that influence and determine the choice for a certain set of impact categories. One obvious one is the availability of the LCIA method in the version of the LCA software used.
Other external factors for this choice will be, among others: requirements following from the defined goal, requirements by the commissioner of an LCA, fixed requirements, e.g. for Environmental Product Declarations (EPDs) or Product Environmental Footprints (PEFs) from underlying sector-based Product Category Rules (PCRs) or from labelling schemes.
Normalisation and weighting
When conducting an LCA, normalisation and weighting are optional steps according to ISO 14044. Normalisation and weighting allow expressing your LCA results by aggregating the results to a single score, giving different weight to the different environmental impacts.
For the PEF, a weighting approach is being developed. Weighting gives a weighting factor to each emission or impact category, and expresses the overall impact into one single unit.
The Dutch Environmental Performance Assessment Method - the LCA rules for Dutch construction, based on EN15804 - has a single score that is currently used a lot in tenders. It's called the Milieukosten indicator (ECI) and expresses the overall environmental impact in monetary value: euro.