Ostracism is practiced by virtually all societies around the world as a means of enforcing cooperation. In this paper, we use a public goods experiment to study whether groups choose to implement an institution that allows for the exclusion of members. We distinguish between a costless exclusion institution and a costly exclusion institution that, if chosen, reduces the endowment of all players. We also provide a comparison with an exclusion institution that is exogenously imposed upon groups. A significant share of the experimental groups choose the exclusion institution, even when it comes at a cost, and the support for the institution increases over time. Average contributions to the public good are significantly higher when the exclusion option is available, not only because low contributors are excluded but also because high contributors sustain a higher cooperation level under the exclusion institution. Subjects who vote in favor of the exclusion institution contribute more than those who vote against it, but only when the institution is implemented. These results are largely inconsistent with standard economic theory but can be better explained by assuming heterogeneous groups in which some players have selfish and others have social preferences.

Climate change damages are expected to increase with global warming, which could be limited directly by solar geoengineering. Here we analyse the views of 723 negotiators and scientists involved in international climate policy who will have a significant influence on whether solar geoengineering will be deployed to counter climate change. We find that respondents who expect severe global climate change damages and who have little confidence in current mitigation efforts are more opposed to geoengineering than respondents who are less pessimistic about global damages and mitigation efforts. However, we also find that respondents are more supportive of geoengineering when they expect severe climate change damages in their home country than when they have more optimistic expectations for the home country. Thus, when respondents are more personally affected, their views are closer to what rational cost-benefit analyses predict. With international climate policy being unable so far to stop and reverse the trend of rising global greenhouse gas emissions 1 , solar geoengineering is increasingly gaining attention. It is in particular discussed as a way to bridge the time until clean technologies are developed and implemented and to respond in case of a climate emergency 2,3. Solar geoengineering, or solar radiation management, aims to cool the earth's surface temperature to counter climate change by partially deflecting the incoming sunlight. The most prominent proposal is to inject aerosol particles into the lower stratosphere to increase deflection of sunlight. Other ideas involve cloud brightening, the deployment of space mirrors, or whitening of rooftops. Solar radiation management could have a rapid effect on temperature and it would be relatively cheap 4-6. The main concern is about the risks and side effects, such as a chemical ozone loss at high latitudes 7,8 , changes in regional precipitation patterns 9 , or the Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Climate negotiation outcomes are difficult to evaluate objectively because there are no clear reference scenarios. Subjective assessments from those directly involved in the negotiations are particularly important, as this may influence strategy and future negotiation participation. Here we analyze the perceived success of the climate negotiations in a sample of more than 600 experts involved in international climate policy. Respondents were pessimistic when asked for specific assessments of the current approach centered on voluntary pledges, but were more optimistic when asked for general assessments of the outcomes and usefulness of the climate negotiations. Individuals who are more involved in the negotiation process tended to be more optimistic, especially in terms of general assessments. Our results indicate that two reinforcing effects are at work: a high degree of involvement changes individuals’ perceptions and more optimistic individuals are more inclined to remain involved in the negotiations.

Using a survey experiment among a special sample composed of art house cinema visitors, we investigate whether spatial climate messages increase subjects' willingness to pay for an inclusion of public transport fares in cinema tickets as well as their willingness to use public transport in case such a combined ticket is introduced. Based on previous findings, we expect emphasizing the positive impact of public transport usage on the local level to have a greater effect on subjects' preferences for public transport than a message that highlights the global consequences. Contrary to these expectations, our results show that the global treatment increases subjects' willingness to pay compared to the local treatment and the baseline. Both treatments increase subjects' willingness to use public transport. Conducting a sub-sample analysis, we find that also the local message increases the willingness to pay for a combined ticket among respondents who lack a financial interest as they already own a season ticket for public transport.

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