For this study, we were interested in time's effect on cooperation. Temporal discounting undermines sustainable resource use—we've known that ever since UBC mathematician Colin Clark published his paper titled "The economics of overexploitation" in 1973 in Science showing that self-interest wasn't the only thing to undermine cooperation and lead to overexploitation of a resource—even under private ownership resources could be exploited due to high rates of discounting.

Since then, many experiments have shown our bias toward instant gratification, and Thomas Schelling has discussed intergenerational discounting with regards to energy use and climate. But our study is the first to test discounting in a group setting.

In behavioral experiments about climate change to date, the set-up was optimistic: participants have received both the benefits of defection and the rewards of cooperation immediately following the experiments. Yet in most real-world collective-risk dilemma, and particularly climate change, the gains from defection can often be realized quickly, but the rewards of cooperation may be delayed by decades.

In our experiment, we gave participants 40 Euros each to invest, as a group of six, towards climate change actions. If participants cooperated to pool together 120 Euros for climate change, returns on their investment in the form of 45 additional Euros each were promised one day later, seven weeks later, or were invested in planting oak trees, and thus would lead to climate benefits several decades down the road—but not personally to the participants.

Although many individuals invested initially in the long-term, intergenerational investment, none of the groups achieved the 120-Euro target, although one group of the 11 total got as close as 116 Euros. 

In a sense, this shows real promise because our experimental was set-up was such that all players were anonymous and punishment and reward weren't available, which means that groups were likely not as cooperative as they would have been if we had introduced the possibilities of punishment, reputation, and even the threat of shame or the promise of honor.

This study confirms our desire to satisfy our desires for the now, rather than the future. But moreover, it represents an advance in experimental design, which we can use to test what kinds of interventions can lower group discount rates and allow us to cooperate to preserve natural resources for future generations. 

Jennifer Jacquet1 *, Kristin Hagel2 , Christoph Hauert3 , Jochem Marotzke4 , Torsten Röhl5 and Manfred Milinski2
The difficulty of avoiding dangerous climate change arises from a tension between group and self-interest1–3 and is exacerbated by climate change’s intergenerational nature4 . The present generation bears the costs of cooperation, whereas future generations accrue the benefits if present cooperation succeeds, or suffer if present cooperation fails. Although temporal discounting has long been known to matter in making individual choices5 , the extent of temporal discounting is poorly understood in a group setting. We represent the effect of both intra- and intergenerational discounting4,6,7 through a collective-risk group experiment framed around climate change. Participants could choose to cooperate or to risk losing an additional endowment with a high probability. The rewards of defection were immediate, whereas the rewards of cooperation were delayed by one day, delayed by seven weeks (intragenerational discounting), or delayed by several decades and spread over a much larger number of potential beneficiaries (intergenerational discounting). We find that intergenerational discounting leads to a marked decrease in cooperation; all groups failed to reach the collective target. Intragenerational discounting was weaker by comparison. Our results experimentally confirm that international negotiations to mitigate climate change are unlikely to succeed if individual countries’ short-term gains can arise only from defection.


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