One Process Does Not Make a Life Cycle—Comment to Marcinkowski and Kopania

In a recent contribution, Ref. [1] study the life cycle impacts of a noise-reducing technology for a combined heat and power plant. The study has merit, because, as the authors observe, most studies that include noise impacts in a life cycle assessment (LCA) focus on transportation noise, ignoring industrial noise. But in another, more fundamental sense, this article presents a step back from previous work [2,3]. As is clear from their Figure 1, Ref. [1] consider the life cycle, from raw materials extraction until waste disposal, and as their Table 2 shows, they do so for a host of impact categories, from climate change to ionizing radiation. But their Figure 1 reveals what they also write explicitly a few lines earlier: “in this study only noise occurring during operation phase was considered”. In other words, noise is not included over the life cycle, thus contradicting the entire idea of LCA. It is not clear then why the authors even cite (“Missing life cycle perspective was raised by Heijungs and Cucurachi”) our previous criticism [4] on another study [5] that only included one process in the life cycle, and that nevertheless claimed to be a life cycle study. Basically, Ref. [1] repeat the set-up of [6], who consider different impact categories (human health, ecosystem, resources) for the life cycle, but noise only for one process (car driving).

The fundamental property of an LCA is that it covers the full life cycle. That is an ambitious task because even a simple product such as a chair consists of different materials, each of which is produced and transported. Those processes invariably involve utility inputs, such as electricity and water, the production and transportation of which involves high-voltage transmission lines, pumps, and many more. Altogether, a standard LCA with popular databases and software nowadays involves 10,000 or more processes, each of which may emit chemical pollutants as well as sound. In practice, some parts may have been excluded, for instance, because their contribution to the system-wide impact is estimated to be negligible. However, an LCA that spans only one process can hardly be called as such.

Why do Ref. [1] include a full life cycle perspective for the traditional impact categories (such as climate change), but do they restrict their scope to one process for sound-related impacts, even though their paper is about noise in a life cycle context? One reason could be that only one process is by far the noisiest process, and that there is no need to include the noise produced by the other 10,000 processes. This is, however, not very likely. Every LCA necessarily includes transportation processes for the materials, products, and equipment, which means a lot of noise sources: trucks, airplanes, harbor cranes, etc. However, although these are noisy, the degree to which they are involved differs per study.

The essential feature of quantitative LCA is that all impacts are included to the extent that they are related to the subject of the study. Let us consider a simple example. If a power plant produces 10 MJ electricity per hour and releases 100 kg CO₂ per hour, it simply emits 10 kg CO₂ per MJ electricity. So if a product requires 5 MJ electricity, the emission is 50 kg. Life gets more complicated if we try to include sound in the same way. Suppose the power plants also generate 100 dB sound. Do we then say it produces 10 dB per MJ? Or perhaps 10 dB × hour per MJ? It is precisely this problem that Ref. [2] took as a starting point. Refs. [1,5,6] may criticize [2] for having certain “drawbacks” or to “overestimate” the impacts, but these contributions fail to address the fundamental question: how to add sound across different sound-generating processes along the life cycle? Ref. [1] suggested a possible solution to this issue. We think that Ref. [1] have made a valuable study showing the trade-off of decreasing noise and increasing other impacts, but they have missed the opportunity to test in practice the scientific challenges of quantifying noise in LCA.