Action to tackle the complex and divisive issue of climate change will be strongly influenced by public perception. Online social media and associated social networks are an increasingly important forum for public debate and are known to influence individual attitudes and behaviours - yet online discussions and social networks related to climate change are not well understood. Here we construct several forms of social network for users communicating about climate change on the popular microblogging platform Twitter. We classify user attitudes to climate change based on message content and find that social networks are characterised by strong attitude-based homophily and segregation into polarised "sceptic" and "activist" groups. Most users interact only with like-minded others, in communities dominated by a single view. However, we also find mixed-attitude communities in which sceptics and activists frequently interact. Messages between like-minded users typically carry positive sentiment, while messages between sceptics and activists carry negative sentiment. We identify a number of general patterns in user behaviours relating to engagement with alternative views. Users who express negative sentiment are themselves the target of negativity. Users in mixed-attitude communities are less likely to hold a strongly polarised view, but more likely to express negative sentiment towards other users with differing views. Overall, social media discussions of climate change often occur within polarising "echo chambers", but also within "open forums", mixed-attitude communities that reduce polarisation and stimulate debate. Our results have implications for public engagement with this important global challenge

Understanding human behavior lies at the heart of responses to climate change. Many environmentally relevant behavior patterns are frequent, stable, and persistent. There is an increasing focus on understanding these patterns less in terms of deliberative processes and more in terms of habits and routines embedded in everyday life. Examinations of the ‘habitual’ nature of environmentally consequential activities have been approached from two theoretically distinct perspectives. From a social psychological perspective, ‘habit’ is studied as an intra‐individual psychological construct that sustains ingrained behavior patterns in stable settings and obstructs adoption of more environmentally friendly alternatives. Sociologists from the social practice tradition, in contrast, have sought to highlight the ways in which resource‐intensive ‘habitual practices’ become established and maintained in society through a commingling of material, procedural, and socio‐discursive elements. We reflect critically upon key theoretical differences underpinning these two approaches to repetitive behaviors and review empirical work from both traditions that speaks to the relevance of ‘habitual behavior patterns’ central to addressing climate change. Finally, we examine how changes in habits are theorized and operationalized within both social psychological and social practice approaches, and practical implications for promoting environmentally sustainable societies. WIREs Clim Change 2015, 6:113–128. doi: 10.1002/wcc.327This article is categorized under: Perceptions, Behavior, and Communication of Climate Change > Behavior Change and Responses