Ideological biases in social sharing of online information about climate change

ramifications. These findings suggest greater focus and coherence amongst the right-wing and climate-sceptic frames and support the findings of [37], with greater fragmentation amongst the left-wing and environmentalist frames; this may partly reflect the larger size of the left- wing/environmentalist cluster in the information-sharing network, which permits greater internal differentiation. Consistency of network structure over time To understand the consistency of the polarised information-sharing process over time, the network structure was examined along with similarity/persistence of the sets of users, source domains and shared URLs (articles) across all weeks in the study period. Similarity scores are reported in Table 3. Fig 7 presents the network diagrams of the remaining six weeks in our study period (Weeks 1 − 3 & 5 − 7). In each week, a similar division into two clusters is observed in the information-sharing network, although the specific composition of the users and shared articles that form the net- work changes substantially over time. The number of communities in the left-hand and right- hand clusters varies over the weeks and the relative sizes of the different communities also change. However, each week reveals the same broad pattern of a larger left-wing/environmen- talist cluster split into several smaller sub-communities, with a smaller right-wing/sceptic clus- ter, showing that this pattern is not an artefact of the increased activity during Week 4. Taken together with Fig 3, these results demonstrate that the pattern of network division persists over

time, spanning multiple weeks of ‘normal’ activity and one exceptional week of high media activity. Considering the inter-week similarity between user populations and the source domains and URLs they shared, Table 3 shows the inter-week similarity of unique users, URLs and web- site domain shares, along with the minimum, mean, maximum and standard deviation of pair- wise similarity measures. The shared articles in Table 3b show the lowest similarity between weeks, with a slightly higher similarity between adjacent weeks. Intuitively, the source domains Table 2. Characterisation of the five largest communities in Week 4. Community 1 This is the largest community and is dominated by mainstream media outlets, such as The Guardian and The Independent, mostly from the UK. This community includes mainstream news reporting and discusses the Paris Agreement on climate change almost exclusively, focusing on the consequences of President Trump’s decision and any international responses. Community 2 This community includes many right-wing sources, including alternative news sites such as Breitbart and The Daily Caller. Social media sites are also prominent in this community as Facebook, Twitter, and Gab all appear, suggesting that this group captures attempts to use Twitter to re-share content from other social platforms. Some established media outlets such as The Daily Mail and Fox News are present, but are less focused in this community than alternative news sites. This community also discusses the Paris Agreement decision made by President Trump, as well as

certain aspects of climate science. This is the only community to focus on former US politicians Obama and Gore and the phrase global warming dominates the bigram cloud (Fig 6c). Community 3 This community consists of many mainstream domains revealing a US focus. The most prominent domains here are established mainstream media sources such as the Washington Post and New York Times. As with Community 1, the Paris Agreement on climate change is a key topic of interest. Community 4 This community includes a number of alternative and smaller news media domains with a mostly left-wing bias, such as Daily Kos and Mother Jones, amongst established mainstream news sources. The content here is similar to that of Community 1 and Community 3, but also references then US Environmental Protection Agency Administrator Scott Pruitt and Michigan congressman Tim Walberg for their comments around climate change. Community 5 This community is comprised of a mix of social media, news and commentary sites. Again, the Paris Agreement decision is a focus, with additional framing around global consequences and opinion- pieces on the decision. https://doi.org/10.1371/journal.pone.0250656.t002 PLOS ONE Ideological biases in social sharing of online information about climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0250656 April 23, 2021 16 / 25