The collective-risk social dilemma and the prevention of simulated dangerous climate change

Abstract

Will a group of people reach a collective target through individual contributions when everyone suffers individually if the target is missed? This "collective-risk social dilemma" exists in various social scenarios, the globally most challenging one being the prevention of dangerous climate change. Reaching the collective target requires individual sacrifice, with benefits to all but no guarantee that others will also contribute. It even seems tempting to contribute less and save money to induce others to contribute more, hence the dilemma and the risk of failure. Here, we introduce the collective-risk social dilemma and simulate it in a controlled experiment: Will a group of people reach a fixed target sum through successive monetary contributions, when they know they will lose all their remaining money with a certain probability if they fail to reach the target sum? We find that, under high risk of simulated dangerous climate change, half of the groups succeed in reaching the target sum, whereas the others only marginally fail. When the risk of loss is only as high as the necessary average investment or even lower, the groups generally fail to reach the target sum. We conclude that one possible strategy to relieve the collective-risk dilemma in high-risk situations is to convince people that failure to invest enough is very likely to cause grave financial loss to the individual. Our analysis describes the social window humankind has to prevent dangerous climate change.

Fig. 1.

Groups that either reach the target or fail. Displayed is the percentage of groups of six subjects each that fail to invest the target sum of at least €120 during 10 climate rounds, when they have a probability of 90%, 50%, or 10% of losing all their savings if the target sum is not reached. There are differences in not reaching the target among treatments (P = 0.008, n = 30, df = 2,29, χ² = 9.66). The percentage of groups not reaching the target is significantly different from all groups reaching the target in each treatment (in each case: n = 10, P < 0.0001, binomial test).

Fig. 2.

Cumulative sum of money per group and round provided for the climate account. The target sum to be achieved after 10 rounds was €120; the treatments differed in the probability, i.e., 90%, 50%, and 10%, with which all subjects in a group lost their individual savings when the group did not supply the target sum for the climate account.

Fig. 3.

Strategic behavior of subjects depending on the risk of losing all savings. Number of selfish acts, i.e., providing €0 (unfilled columns); fair-share acts, i.e., providing €2 (light-gray shading); and altruistic acts, i.e., providing €4 (dark-gray shading), per group of six subjects in the first (rounds 1–5, left in column pair) and second halves (rounds 6–10, right in column pair). The probability of losing all savings if the target sum is not reached was 90%, 50%, or 10%, for a, b, and c, respectively. See text for statistics.