This thesis investigates the importance of communication for individual cooperation in large-scale collective action dilemmas. In small-scale collective action, where participants have the possibility to meet face-to-face, communication has been shown to drastically increase levels of cooperation. These positive effects are generally believed to be related to the possibilities of exchanging mutual commitments, sharing strategic information, creating and enforcing shared norms, developing trust, and creating a common group identity that communication offers. In large-scale dilemmas, involving thousands or even millions of participants, possibilities for communication are highly restricted beyond the immediate social vicinity of individuals. Participants are therefore unable to reap the positive benefits of communication that are available at the small-scale. Furthermore, as the public goods on which individuals cooperate in large-scale dilemmas often are both distant and abstract in nature (climate change, ozone depletion, overpopulation), the role of communication as an informational-shortcut might be even greater in large-scale dilemmas. That is, individuals need information about the characteristics of the resource in question, the relevant set of other actors participating, and the individual costs and benefits of cooperation.

To compensate for the lack of communication and first-hand information, individuals in large-scale dilemmas are generally assumed to rely on different forms of judgmental and behavioral ‘heuristics’ (e.g. generalized trust and internalized norms) to make cooperative decisions. In this thesis I focus on one type of heuristic that generally has been overlooked in research on collective action; the individual reliance on information from trusted elite sources. Specifically, I study the extent to which individuals use communications from political parties when making cooperative decisions. The aim of the thesis is thus to investigate the relationship between political communication and large-scale collective action, and how this relationship varies with individual and contextual factors. This is studied in the context of climate change mitigation, which is a typical case of large-scale collective action, characterized by the large number of anonymous actors, the negligible impacts and high costs of individual cooperation, and a general lack of face-to-face communication and first-hand information.

Using a country comparative approach, and cross-sectional survey data, the results show that: 1) political communications both directly and indirectly (by shaping perceptions of collective efficacy and collective benefits) influences individuals’ cooperative/non-cooperative decisions, and that this effect goes beyond other individual level factors, e.g. ideology, income, education; 2) not only specific communications, but also perceptions of the overall political climate (degree of polarization and the average party stance) affects attitudes both directly and indirectly; 3) these effects are not isolated to certain environments, but (to varying degree) can be found across political contexts and parties. The results have important implications both practically for policy makers, by creating a deeper understanding of the formation of individual climate change attitudes, and theoretically, by creating a better understanding of how individuals make decisions in large-scale collective action dilemmas. Future research should both validate the results from this study using other research designs (e.g. longitudinal or multilevel data, experimental designs), and expand on them, for example by exploring how different sources of communication and different types of information interact and influence the reception of communication content.