It is widely believed that there is strong experimental evidence to support the idea that exogenously imposed regulations crowd out the intrinsic motivations of common pool resource (CPR) users to refrain from over-harvesting. We introduce a novel experimental design that attempts to disentangle potential confounds in previous experiments. A key feature of our experimental design is to have the exact same regulations chosen endogenously as those that are imposed exogenously. When we compare the same regulations chosen endogenously to those externally imposed, we observe no differences in extraction levels among CPR users in a laboratory experiment. We also observe no differences between weak external regulations and no regulations, after controlling for a potential confound. However, when we add communication to our endogenous treatment, we observe significant behavioral differences between endogenous regulations with communication and exogenous regulations without communication. Our results suggest that externally imposed regulations do not crowd out intrinsic motivations in the lab and they confirm that communication facilitates cooperation to reduce extraction. 1 Ostrom, like many scholars who cite Cardenas et al. (2000), misinterpreted slightly how Cardenas et al. (2000) reached their conclusion. She states that "subjects [in the regulation treatment] increased their withdrawal levels when compared to the outcomes obtained when face-to-face communication was allowed and no rule was imposed" (Ostrom 2009). However, their crowding out effect comes from a within-subjects analysis of their regulation treatment, not a between-subjects analysis between their regulation and communication treatments. That is, within their regulation treatment, Cardenas et al. (2000) observe higher individual extraction when an external regulation is weakly imposed compared to when no regulation is imposed.2 All of our results are remarkably consistent with each other. In our experimental context, we find no evidence that exogenously imposing regulations crowds out motivations to refrain from extraction. We show clearly that communication and strategic learning matter. If previous work has sometimes confounded communication with endogenous regulation and confounded strategic learning with exogenous regulation, then it is not surprising that existing results appear to contradict each other. Our aim is to use a simple experimental design to clear up some of this confusion. We start by reviewing the literature on external regulation and intrinsic motivation in Section 2, before giving a detailed description of our experimental design in Section 3. Section 4 summarizes our results and Section 5 concludes.

Climate engineering—the deliberate large-scale manipulation of the Earth’s climate system—is a set of technologies for reducing climate-change impacts and risks. It is controversial and raises novel governance challenges [T. C. Schelling,Climatic Change, 33, 303–307 (1996); J. Virgoe,Climatic Change, 95, 103–119 (2008)]. We focus on the strategic implications of solar geoengineering. When countries engineer the climate, conflict can arise because different countries might prefer different temperatures. This would result in too much geoengineering: the country with the highest preference for geoengineering cools the planet beyond what is socially optimal at the expense of the others—a theoretical possibility termed “free-driving” [M. L. Weitzman,Scand. J. Econ.,117, 1049–1068 (2015)]. This study is an empirical test of this hypothesis. We carry out an economic laboratory experiment based on a public “good or bad” game. We find compelling evidence of free-driving: global geoengineering exceeds the socially efficient level and leads to welfare losses. We also evaluate the possibility of counteracting the geoengineering efforts of others. Results show that countergeoengineering generates high payoff inequality as well as heavy welfare losses, resulting from both strategic and behavioral factors. Finally, we compare strategic behavior in bilateral and multilateral settings. We find that welfare deteriorates even more under multilateralism when countergeoengineering is a possibility. These results have general implications for governing global good or bad commons.

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