Abstract: This article presents a multi-method research design for measuring the (trans-)national quality of issue publics on Twitter. Online communication is widely perceived as having the potential to overcome nationally bound public spheres. Social media, in particular, are seen as platforms and drivers of transnational communication through which users can easily connect across borders. Transnational interactivity can be expected in particular for policy fields of global concern and elite or activist communication as practiced on Twitter. Nevertheless, there is still a lot of evidence for the enduring national structuration of political communication and publics as it results from a shared language (mostly), culturally defined media markets, established routines of social and political communication, and sociocultural stocks of knowledge. The study goes beyond measuring user interaction and also includes indicators of cross-referential cohesion. It applies a set of computational methods in network and discourse analysis and presents empirical evidence for Twitter communication on climate change being a prime issue of global concern and a globalized policy agenda. For empirical analysis, the study relies on a large Twitter dataset (N ≈ 6m tweets) with tweet messages and metadata collected between 2015 and 2018. Based on basic measurements such as geolocation and language use, the metrics allowed measurement of cross-national user interactions, user centrality in communicative networks, linking behaviour, and hashtag co-occurrences. The findings of the exploratory study suggest that a combined perspective on indicators of user interaction and cross-referential cohesion helps to develop a better and more nuanced understanding of online issue publics.