Ideological biases in social sharing of online information about climate change

from the two main clusters is youtube.com/watch. This node is difficult to interpret as it aggre- gates many YouTube video links, seemingly from all sides of the debate. We cannot verify this with our text-based content analysis. There is a strong correlation between opinions about climate change and political ideology expressed in shared content. Fig 4 plots the position of the 62 web domains on axes of climate bias and political bias, based on content of articles coded by the panel. Left-right political ideol- ogy and environmentalist-sceptic climate opinions are very strongly correlated (Pearson’s r = 0.86) and very few domains appear in the right-wing/environmentalist and left-wing/scep- tic quadrants. Mapping ideologies/opinions associated with web domains onto the information-sharing network structure shows an association between network position and viewpoint. Fig 5 shows the network diagram from Fig 3 with URL-node colours altered to show biases in the political/ climate opinions expressed by their web domains. Fig 5a colours the nodes to highlight the left-right political bias. The left-hand cluster contains predominantly left-wing sites. The right- hand cluster has a high concentration of right-wing sites, but also has many uncoded sites. A similar pattern can be seen in Fig 5b, which colours nodes by climate change bias, with the left-hand cluster predominantly environmentalist and the right-hand cluster containing most Fig 3. Information-sharing networks are polarised. Plot shows the URL co-sharing network for the week in which the US withdrawal

from the Paris Agreement was announced (Week 4 of the study period). The five largest communities by total share count are displayed (67.69% of 7, 496 nodes). Communities 1 − 5 are coloured blue, yellow, green, red and purple respectively and node size is proportional to the square root of total share count. Node placement uses a force-directed algorithm [50] which groups densely connected nodes together; this layout highlights two large clusters, with four communities on the left and a single community on the right. https://doi.org/10.1371/journal.pone.0250656.g003 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 12 / 25