## 4 Conclusions  
In this study, the CO\({}_{2}\) emissions of Japanese online music and video streaming in 2019 were estimated using the LCA. The system boundary consisted of processes related to data center construction and server manufacturing, listening to and/or watching by the users, and data center and server disposal. Life cycle CO\({}_{2}\) emission per 1 MB of communication volume was calculated in this study. In particular, it was found that ICT equipment, such as PCs and smartphones, was used for listening and/or watching music and/or videos, and different streaming types were used, such as subscription-based or free. Based on these scenarios, the life cycle CO\({}_{2}\) emissions based on ICT equipment and type of streaming were estimated. It was found that listening and/or watching by the users resulted in the highest CO\({}_{2}\) emissions among all the processes. Life cycle CO\({}_{2}\) emissions from online music streaming through PCs and smartphones were 5.88 \(\times\) 10\({}^{-4}\) and 1.43 \(\times\) 10\({}^{-4}\) kg-CO\({}_{2}\)/MB, respectively. For online music streaming, CO\({}_{2}\) emissions from PCs were approximately 4.1 times higher than those for smartphones. The overall CO\({}_{2}\) emissions from Japanese online music and video streaming in 2019 were approximately 922 thousand t-CO\({}_{2}\). The ratio of the CO\({}_{2}\) emissions of music and videos accounted for 12.3% and 87.7%, respectively. The ratio of CO\({}_{2}\) emissions from online music and video streaming to those from domestic energy generation was 0.21%. With an increase in users, CO\({}_{2}\) emissions may increase to up to 1545 thousand t-CO\({}_{2}\) in 2025.  
Japan should actively engage in technological innovation, as it is an important aspect, and was included in Japan's science and technology policy \"Society 5.0\". Although its importance from an environmental perspective has been discussed, the results obtained in this study revealed that CO\({}_{2}\) emissions should not be ignored. When promoting ICT, it is necessary to not only pursue convenience, but also simultaneously evaluate the environmental impacts. [PERSON] and [PERSON] [52] indicated that ICTs have great potential for reducing energy consumption, but this realization depends upon wider economic and political conditions. The national government should assess the ways to reduce environmental impact by promoting ICT. In addition, consumers should also be aware of not only the convenience associated with online music and video streaming, but also  
Figure 2: Future projection of CO\({}_{2}\) emission derived from music and videos streaming in Japan.  
the associated environmental perspective. In future, efforts to reduce the environmental impacts derived from the ICTs should be examined using LCA.  
Conceptualization: T.T.; methodology: T.T. and T.Y.W.; validation: T.T.; formal analysis: T.T. and T.Y.W.; investigation: T.T.; resources: T.Y.W.; writing--original draft preparation: T.T.; writing--review and editing: T.T.; visualization: T.Y.W.; supervision: T.T.; project administration: T.T. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data are obtained from [6; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45].  
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.  
The authors declare no conflict of interest.