The collective-risk social dilemma and the prevention of simulated dangerous climate change
- Manfred Milinski*,†,
- Ralf D. Sommerfeld*,
- Hans-Jürgen Krambeck*,
- Floyd A. Reed‡, and
- Jochem Marotzke†,§
- *Department of Evolutionary Ecology, Max Planck Institute for Evolutionary Biology, 24306 Plön, Germany;
- ‡Department of Biology, University of Maryland, College Park, MD 20742-5815; and
- §Department of “The Ocean in the Earth System,” Max Planck Institute for Meteorology, 21046 Hamburg, Germany
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Edited by Robert May, Oxford University, Oxford, United Kingdom, and approved December 18, 2007 (received for review October 8, 2007)
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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).
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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.
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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.
Footnotes
- †To whom correspondence may be addressed. E-mail: milinski{at}mpil-ploen.mpg.de or jochem.marotzke{at}zmaw.de
- © 2008 by The National Academy of Sciences of the USA
