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ENVIRONMENTAL SCIENCES
The collective-risk social dilemma and the prevention of simulated dangerous climate change
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*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
Edited by Robert May, Oxford University, Oxford, United Kingdom, and approved December 18, 2007 (received for review October 8, 2007)
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.
cooperation | public good | threshold
Author contributions: M.M., R.D.S., F.A.R., and J.M. designed research; M.M. and R.D.S. performed research; H.-J.K. contributed new reagents/analytic tools; M.M. analyzed data; and M.M., R.D.S., F.A.R., and J.M. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
See Commentary on page 2261.
This article contains supporting information online at www.pnas.org/cgi/content/full/0709546105/DC1.
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
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  A. Dreber and M. A. Nowak Gambling for global goods PNAS, February 19, 2008; 105(7): 2261 - 2262. [Full Text] [PDF]
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