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The evolution and long-term sustenance of cooperation has consistently piqued scholarly interest across the disciplines of evolutionary biology and social sciences. Previous theoretical and experimental studies on collective risk social dilemma games have revealed that the risk of collective failure will affect the evolution of cooperation. In the real world, individuals usually adjust their decisions based on environmental factors such as risk intensity and cooperation level. However, it is still not well understood how such conditional behaviours affect the evolution of cooperation in repeated group interactions scenario from a theoretical perspective. Here, we construct an evolutionary game model with repeated interactions, in which defectors decide whether to cooperate in subsequent rounds of the game based on whether the risk exceeds their tolerance threshold and whether the number of cooperators exceeds the collective goal in the early rounds of the game. We find that the introduction of conditional cooperation strategy can effectively promote the emergence of cooperation, especially when the risk is low. In addition, the risk threshold significantly affects the evolutionary outcomes, with a high risk promoting the emergence of cooperation. Importantly, when the risk of failure to reach collective goals exceeds a certain threshold, the timely transition from a defective strategy to a cooperative strategy by conditional cooperators is beneficial for maintaining high-level cooperation. [ABSTRACT FROM AUTHOR]

Human society and natural environment form a complex giant ecosystem, where human activities not only lead to the change in environmental states, but also react to them. By using collective-risk social dilemma game, some studies have already revealed that individual contributions and the risk of future losses are inextricably linked. These works, however, often use an idealistic assumption that the risk is constant and not affected by individual behaviors. Here, we develop a coevolutionary game approach that captures the coupled dynamics of cooperation and risk. In particular, the level of contributions in a population affects the state of risk, while the risk in turn influences individuals’ behavioral decision-making. Importantly, we explore two representative feedback forms describing the possible effect of strategy on risk, namely, linear and exponential feedbacks. We find that cooperation can be maintained in the population by keeping at a certain fraction or forming an evolutionary oscillation with risk, independently of the feedback type. However, such evolutionary outcome depends on the initial state. Taken together, a two-way coupling between collective actions and risk is essential to avoid the tragedy of the commons. More importantly, a critical starting portion of cooperators and risk level is what we really need for guiding the evolution toward a desired direction.

A social dilemma implies that individuals will choose the defection strategy to maximize their individual gains. Reward is a powerful motivator to promote the evolution of cooperation, thus addressing the social dilemma. Nevertheless, it is costly since we need to monitor all participants in the game. Inspired by these observations, we here propose an inexpensive protocol, a so-called sampling reward mechanism, and apply it to social dilemmas, including public goods game and collective-risk social dilemma. More precisely, the actual usage of reward depends on the portion of cooperators in the sample. We show that the average cooperation level can be effectively improved under high reward threshold and high reward intensity, albeit at the expense of reward cost. It is intriguing to discover that for the latter aspect, there is a critical threshold at which further increases in reward intensity have no significant effect on improving the cooperation level. Moreover, we find that the small sample size favors the evolution of cooperation while an intermediate sample size always results in a lower reward cost. We also demonstrate that our findings are robust and remain valid for both types of social dilemmas.

Punishment is a key incentive to maintain cooperation. But it is costly, hence its effectiveness is under permanent debate. To overcome this difficulty, we here introduce a sampling punishment method and explore its consequences on public goods game and collective-risk social dilemma. In our model, just a small portion of participants are sampled and defectors are punished only if their portion exceeds a certain threshold. We show that the cooperation level can be effectively improved under low punishment threshold and small sample size when the punishment intensity is considerable. To identify the optimal conditions of sampling punishment, we monitor the punishment probability and related cost. We find that the adoption of a low punishment threshold and a small sample size under a considerable punishment intensity is the best, which always leads to a high cooperation level with a low related cost. Our observations are both valid in these two games. • The introduction of the sampling punishment mechanism can facilitate the emergence of cooperation. • A low punishment threshold and a small sample size are beneficial for cooperation. • Our observations are both valid in the public goods game and collective-risk social dilemma game. [ABSTRACT FROM AUTHOR]

To solve problems like climate change, every little push counts. Community energy schemes are a popular policy targeted to reduce a country’s carbon emissions but the effect they have on energy use depends on whether people can work together as a community. We often find ourselves caught in a dilemma: if others are not doing their bit, why should I? In our experiment participants (N = 118) were matched in groups of 10 to play in a collective-risk game framed as a community energy purchase scheme. They made only one decision about energy use for their virtual household a day, whilst a full round of the game lasted one week in real time. All decisions were entered via personal phone or a home computer. If in the end of the week the group exceeded a pre-paid threshold of energy use, all group members would share a fine. Each day participants received feedback about decisions of their group partners, and in some groups the feedback was manipulated as high (unfair condition) or low (fair condition) use. High average group use created individual risk for participants to be penalized in the end of the week, even if they did not use much themselves. We found that under the risk of having to pay a fine, participants stayed significantly below the fair-share threshold regardless of unfair behaviour of others. On the contrary, they significantly decreased their consumption towards the end of the game. Seeing that others are doing their bit – using a fair-share – encouraged people to take advantage of the situation: those who played against fair confederates did not follow the normative behaviour but conversely, increased their consumption over the course of the game. These opportunistic strategies were demonstrated by impulsive participants who were also low in punishment sensitivity. We discuss the findings in the light of policy research as well as literature on cooperation and prosocial behaviour.

The landmark agreement recently negotiated in Paris represents an ambitious plan to combat climate change. Nevertheless, countries' current climate pledges are insufficient to achieve the agreement's goal of keeping global mean temperature rise 'well below' 2 C. It is apparent that climate negotiators need to be equipped with additional strategies for fostering cooperation if a climate catastrophe is to be averted. We review the results arising from an emerging literature in which the problem of avoiding dangerous climate change has been simulated using cooperation experiments in which individuals play a game requiring collective action to avert a catastrophe. This literature has uncovered five key variables that influence the likelihood of avoiding disaster: (1) the perceived risk of collective failure, (2) inequalities in historical responsibility, wealth, and risk exposure, (3) uncertainty surrounding the threshold for catastrophe, (4) intergenerational discounting, and (5) the prospect of reward or punishment based on reputation. Along with the results of a recent experimental assessment of the key instruments of the Paris Agreement, we consider how knowledge of the effects of these variables might be harnessed by climate negotiators to improve the prospects of reaching a solution to global climate change. [ABSTRACT FROM AUTHOR]

Abstract: We analyze the effect of “milestones” on reaching a long-term target, which if missed implies dramatic payoff risks. In our experiment, a cumulative threshold public goods game, milestones are captured by intermediate contribution targets on the way to the final target. Missing the final target leads to a probabilistic total loss for all players, and missing intermediate targets may lead to the same consequences even earlier. The additional intermediate targets feature environmental protection as a process rather than a contest for reaching a final target. The regulating agency is Nature, although political agencies might implement a similar regulation. We test milestone effects by varying the size of milestones in addition to changing the marginal productivity of individual contributions and the payoff risk. Although we observe some milestone effects, additional regulation by milestones on its own does not guarantee that targets are reached. [Copyright &y& Elsevier]

Avoiding a catastrophic climate-change event is a global public good characterized by several dimensions, notably heterogeneity between the parties involved. It is often argued that such heterogeneities between countries is a major obstacle to cooperative climate policy. We use a stylized game mimicking basic features of the climate-change dilemma to experimentally study the effect of two important heterogeneities, wealth and loss when a catastrophic event occurs. We find that under loss heterogeneity the success rate in achieving sufficient mitigation to prevent a catastrophic event is higher than under symmetry. Moreover, neither endowment heterogeneity nor the combination of endowment and loss heterogeneities lead to significantly different success rates than under symmetry. These findings suggest that heterogeneities may in fact facilitate rather than hinder successful cooperation in catastrophe prevention. [ABSTRACT FROM AUTHOR]