How we compute our emission factors
Posted at 2022-11-01 16:29:07 by Matthew
If you have browsed around our website, you will have noticed that we compute a weighted average across multiple studies to arrive at an emission factor for a specific product. Each resource is weighted according to credibility. Papers published in peer reviewed journals are weighted the highest and resources that are not peer reviewed, are outdated or lack proper documentation will be weighted less. To make this process more reproducible, we devised a fixed set of criteria to weigh the reliability of different resources in a (semi-)objective way.
The weights go from 0 to 10, meaning that a source rated 5, will only have half as much influence on the emission factor as a source rated 10. Each resource starts with a weight of 10 and receives penalty points for each indication of unreliability. If a resource receives more than 10 penalty points, we do not consider it in the weighted average, though we might leave the resource in our database for research purposes.
In the scientific community, peer reviewed articles are the golden standard for assessing the quality and reliability of a work of research. The peer review process ensures that the methodology and results are checked by an independent expert in the field. To keep matters simple, we decided not to consider the number of citations of the article, nor the impact factor of the journal.
- Not peer reviewed: -2 points
Number of products
Some resources attempt to estimate greenhouse gas emissions for a large number of products, using a standardized LCA methodology. Although it is useful that the same methodology is applied to all products, it often requires simplifying assumptions to fit all processes in the same framework. We have noted that estimates from such resources frequently substantially differ from studies that only evaluate a single product.
- >= 10 products: -2 points
We have a small number of resources that are meta studies, i.e., studies that average emission factors across multiple studies. LiveLCA in itself can be considered a meta study. On the one hand, combining multiple studies is a good thing, as this stabilizes the emission estimate. On the other hand, it is often hard to verify the quality of the individual resources. As these two factors are at odds with each other, we decided not to penalize nor reward meta studies.
Sponsored / commissioned studies For a small number of products, we included studies which were sponsored or commissioned by a company that have a particular interest in a specific study outcome. Although such studies could have been well performed and unbiased, it is not hard to imagine that the most favorable numbers have been chosen to promote a producer’s interest. We distinguish between studies that were directly sponsored or commissioned and those that have been (partially) funded through stakeholder organizations.
- Funded by a stakeholder organization: -2 points
- Directly sponsored / commissioned: -5 points
Year of study
The field of sustainability research has evolved rapidly in the last decades. Methodologies, primary data and databases have improved and (hopefully) are able to provide more accurate data now compared to 10 years ago. We have, somewhat arbitrarily, chosen to consider studies conducted before the release of the ISO 14044 standard in 2006 as outdated.
- Before 2006: -3 points
To be able to verify the quality of a study, it should first of all be clear how the researchers arrived at the results. This criterion is fulfilled for practically all peer reviewed studies. However, for reports from governmental organizations or even commercial parties, a well described methodology increases the reliability of the results.
- Partially described: -1 point
- Not described: -3 points
Reputation of source
In principle, anyone can perform an LCA analysis. However, depending on the training and experience of the conductors of the study the results will be more or less reliable. For example, a study performed by undergraduate students in an LCA course is more likely to overlook important factors in the emission calculations or make unrealistic assumptions than a study conducted by researchers working with LCAs for many years.
- Low reputation: -3 points