What are the advantages and disadvantages of using midpoint and endpoint indicators in LCA?

Based on my experience in the metal processing industry, using a combination of midpoint and endpoint indicators is essential for a comprehensive environmental impact assessment. Midpoint indicators help understand the immediate environmental effects, such as emissions and resource use, while endpoint indicators provide a holistic view of long-term consequences like human health impacts and biodiversity loss. By considering both types of indicators, we can make informed decisions, identify improvement opportunities, and enhance sustainability practices in the industry.

In my experience with environmental impact assessment, midpoint indicators have proven instrumental, particularly when delving into the complexities of plastic pollution. Take, for instance, the examination of resource depletion associated with the life cycle of plastic products. For example, when comparing the environmental footprint of different plastic materials, midpoint indicators streamline calculations by providing an intermediate measure close to the source of emissions. This expedites assessments and facilitates scenario comparisons, allowing for quicker decision-making in efforts to address plastic pollution and enhance sustainability in the plastics industry.

When you calculate based on midpoint indicators, the result is by definition more accurate (than with endpoints). The impact assessment methods are generally based on known physical phenomena, so when things are considered equivalent, there's generally an objective basis for it. The alternative (endpoints) generally requires some more abstract form of aggregation (e.g. how much each of those effects damage ecosystems), which is bound to include more judgement calls on behalf of the method developers. Midpoint indicators are generally also more educational, since they point at very specific environmental phenomena, that endpoints unavoidably hide.

In the context of plastic pollution, let's consider the endpoint indicator of "Ecosystem Quality." This indicator assesses the long-term impact of plastic waste on ecosystems, biodiversity, and overall environmental health. By using endpoint indicators, we can gauge not only the resource depletion or emissions associated with plastic but also understand the potential harm to marine life, terrestrial ecosystems, and the services they provide to humans.

Endpoint indicators are great at giving a big picture over a category, or even all categories. For example: most people can easily grasp what "impact on human health" means (less so the units in which it's measured). Also, most non-LCA people think in such abstract terms, and not in the level of detail needed for e.g. midpoint indicators. They might not know of all the environmental impacts that influence ecosystem quality, and not want to learn about them just now! Therefore, endpoint indicators tend to be good for decision-making and dissemination.

A balanced combination of midpoint and endpoint indicators is advised to capture both immediate environmental changes and broader consequences for human well-being and ecosystems. Stakeholder involvement adds valuable perspectives to indicator selection, incorporating viewpoints from experts, community members, and other affected parties.

The most important criterion to think about in choosing indicators is the audience and intent of the study. Who's going to read it? What do they need to decide based on it? What do they know? What do they need to know? The best result is generally a combination of both, but how deep such combination goes depends on that audience and intent. If you're sharing among scientists, you almost need a whole set of midpoint indicators. And if you are involving a very diverse audience for dissemination, you should probably bias heavily towards endpoint indicators. And of course, sometimes what you need to do is get your LCA certified somewhere, so those indicators have been chosen for you anyways!

Advantages of midpoint indicators include quantitative analysis, providing detailed data on environmental stressors like greenhouse gas emissions, aiding in hotspot identification and mitigation prioritization. They rely on readily available data, facilitating easy comparison across products or processes For example, assessing the emissions of ozone-depleting substances (ODS) as a midpoint indicator can highlight areas where phase-out measures are needed in the production process.

Disadvantages of midpoint indicators include their complexity in interpretation as they may not directly correlate with final environmental impacts, such as human health or ecosystem quality. Aggregating multiple midpoint indicators into single scores requires subjective weighting, leading to inconsistent interpretations. For instance, assessing only greenhouse gas emissions as a midpoint indicator may overlook other significant environmental impacts like water pollution or habitat destruction.

Endpoint indicators offer a holistic assessment, simplifying communication by presenting outcomes in terms of meaningful endpoints like human health or ecosystem quality. For example, using disability-adjusted life years (DALYs) as an endpoint indicator provides a clear measure of the overall impact on human health, aiding in decision-making and policy development. Endpoint indicators are often more relevant for decision-making and policy development, as they reflect the ultimate goals of environmental protection and sustainability. For example, policymakers may use endpoint indicators to set environmental targets or regulations aimed at minimizing overall harm to human health or ecosystems.

A clear advantage of endpoint indicators is that they are a bit easier to understand. Biodiversity loss is easier to grasp than terrestrial ecotoxixity or freshwater eutrophication.

Endpoint indicators are inherently less accurate than midpoint indicators because damage pathways are of course only a model of the world and do not 100% reflect the complex reality.

While midpoints are less uncertain and provide more detail, when comparing two things, they also tend to show a lot of trade offs. By assessing with endpoint, we can see how important each midpoint is to what we care about and make good decisions based on the bigger picture.

as an innovation or eample Researchers are looking into using multi-criteria decision analysis (MCDA) methods to bring together midpoint and endpoint indicators in one system. MCDA lets stakeholders weigh various factors (like environmental, social, economic) in decision-making, giving a broader view of product sustainability. Also, improvements in data analytics, machine learning, and big data can enhance the accuracy of LCA models, making environmental impact assessments stronger at both midpoint and endpoint levels.

LCAs are not done in a vacuum, and I find this discussion to be heavily linked to the environment, and to training of the audience. As a company, you need to decide what environmental impacts are your main drivers, so that everybody in the company will be used to talking about those. And then you might define some others that you need to check for burden shifting (or just because they are commonly reported in your industry).