How can we explain variation in the volume and character of transnational collective action on climate change? This paper presents original qualitative and quantitative data to document how transnational activism on climate change has changed over time. The author draws attention to the role of transnational social movement spillover—a process by which ideas, activists, and tactics are diffused from one movement to another—in explaining this evolution. The article examines the spillover of the global justice movement to the climate justice movement from 2007 to 2009, linking this spillover to changes in the nature of activism. In contrast to previous approaches, this work shows that transnational social movement spillover can result in the expansion of contention without radicalizing those actors already involved. This case demonstrates the theoretical importance of the spillover process and offers lessons for future climate activism.
* I thank Scott Byrd, Ruth Reitan, Jackie Smith, Sidney Tarrow, and Andrew Yeo for their helpful comments on this article.