International conferences such as CIRP LCE usually imply that their attendees travel around the world to reach the venue. Several online conferences have already been organised, but the year 2020 was particular because of the COVID-19 pandemics which obliged to cancel or modify dramatically all the events planned from the second quarter of that year. The CIRP Life Cycle Engineering conference was no exception and all arrangements made before March were cancelled or modified in order to host the conference online. This article presents the environmental impact assessment of the online conference and its comparison to the estimation of the impacts if the event had taken place in Grenoble (France), as initially planned. This study confirms that an online conference has lower environmental impacts than a classical conference, except for freshwater quality. The main contributors are the country energy mix of the audience for the online conference and the travel by plane for the classical one. This article also shows that online conferences might contribute to stay within the planetary boundaries. These results encourages to improve the study of the environmental impacts of online conferences and to highlight the hotspots to be improved.