Ostrum, Elinor. 2010. “Polycentric Systems for Coping with Collective Action and Global Environmental Change.” Global Environmental Change. 20:550 – 557.Many problems conceptualized as “global problems” are the cumulative result of actions taken by individuals, families, small groups, private firms, and local, regional, and national governments. A pressing global problem faced in the contemporary world is reducing the emission of greenhouse gases (GHGs) by individuals and organizations around the world that cumulate to increase the threat of major climate change. Solving this problem requires collective action. To avert this global threat, many actors at diverse levels need to make costly decisions to reduce GHG emissions. Everyone benefits from reduced emissions even if they do not contribute any effort themselves (Cole, 2008, Sandler, 2004). As analyzed by distinguished policy analysts, reducing the threat requires an enforceable global treaty (Carraro, 2003, Nordhaus, 1994, Wiener, 2007).(From the Introduction.)