Cooperative interaction of rich and poor can be catalyzed by intermediate climate targets
A letter
Manfred Milinski• Torsten Röhl• Jochem Marotzke
Supplementary online material
Demographic information and composition of subject pool
Students, age range 20 to 28 years, had been recruited from first semester courses in biology at the universities of Hamburg, Kiel and Münster; 96.1 % came from Germany, the rest from other European countries. At each of the three universities, the sequence of trials of the different treatments was completely balanced so that potential sequence effects would cancel out. The gender ratio was, as is usual for biology students in Germany, slightly female biased (62.6 %, similar in all 6 treatments). However in none of the 6 treatments, the proportion of females per group of 6 players correlated significantly with the sum of money collected for reaching the target, e.g., in poor&rich without intermediate climate target: range 1 to 5 women per group, Rho=-.107, z=-0.354, n=12 groups, P=0.72, Spearman rank correlation; with intermediate climate target: range 1 to 6 women per group, Rho=-.284, z=-0.943, n=12 groups, P=0.35, Spearman rank correlation. Thus, no gender effect could be found.
It is likely that being biology students from Germany the participants in the experiment believed in climate change and the anthropogenic role in it, which is certainly true also for the large majority of delegates at climate summits irrespective of the country they come from.
Why did some mixed poor and rich groups miss the final target?
In the mixed groups that missed the final target, the rich could have invested a few € more per person from their operating funds to reach the final target and gain their endowment of €60. The decision rules that have evolved for social dilemma situations are likely to be conditional cooperation rules (Nowak and Sigmund, 1992; Wedekind and Milinski, 1996; Hauert and Schuster, 1997; Gächter and Herrmann, 2009). These rules respond to cooperation with cooperation and to defection with defection, even if the long-term payoff is missed. In the climate game such rules may be difficult to overcome rationally. Moreover, spiteful behaviour (Hamilton, 1979; Johnstone and Bshary, 2004) and other emotion-driven rules such as inequity aversion (Fehr and Schmidt, 1999; Dawes et al., 2007), which are found already in monkeys (Brosnan and De Waal, 2003) may be driving the interaction of rich and poor countries to some extent.
Yet means to overcome such rules do exist, namely by the need for improved social reputation gained through cooperation, i.e. “indirect reciprocity” (Milinski et al., 2002; Milinski et al., 2006) costly punishment (Yamagishi, 1986; Fehr and Gächter, 2002; Gürerk et al., 2006) or a combination of reputation and sanctioning institutions (Rockenbach and Milinski, 2006; Hilbe and Sigmund, 2010; Milinski and Rockenbach, 2011). Future research might show whether these means are of any help for the interaction of countries in the climate change game (Inman 2009).
SOM-Fig. 1 Percentage of groups that reached the intermediate or final climate target, without and with intermediate climate target announced. (a) groups of 6 poor subjects; (b) groups of 6 rich subjects; (c) mixed groups of 3 poor and 3 rich subjects. See main text for statistics.
References
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Written Instructions for the Subjects
Instructions for treatment “rich and poor with intermediated climate target announced”, translated from the written German text that the subjects had to read before the experiment.
Welcome to this experiment, during which you can earn money!
At the beginning of this experiment, you will receive either 100 Euros (rich) or 50 Euros (poor) credited on your account.
Thereof 40 Euros (rich) or 20 Euros (poor) is your “operating fund”, from which you can invest money during the game. The remaining 60 Euros and 30 Euros, respectively, are your “endowment” that you can’t use during the game.
During the game you can decide whether to invest money from your operating fund.
In any case, you will receive in cash the remaining amount of money from the operating fund at the end of the game.
Your decisions are anonymous. To ensure this, the computer assigns a pseudo name to you that can be seen at the bottom left of your screen. The pseudo names are names of the moons in our solar system (Ananke, Telesto, Despina, Japetus, Kallisto or Metis).
To render this experiment successful, it is strictly forbidden that players talk to each other
or communicate in any way.
You have to confirm information in the course of the game by pressing the “OK” button.
After reading this text completely, please confirm by pressing the OK-button.
In the course of this experiment you will play exactly 10 climate rounds.
In these rounds you can invest in an attempt to protect the climate and avoid dangerous climate change. The consequences of dangerous climate change will include significant economic losses, as well as other consequences. This is simulated in this experiment by the potential loss of your endowment at the end.
You are paid the sum remaining from your operating fund in any case.
In each round of the climate game all six players are asked simultaneously:
“How much money do you want to invest in climate protection?”
(possible answers: 0, 2 or 4 Euros)
You cannot invest more than your operating fund allows. The computer does not accept overdraft. Only after each player has decided, the six decisions will be displayed simultaneously. Afterwards, all amounts paid will be credited into an account for climate protection by the computer.
With the money you may have paid into the climate account, we will place an advertisement in a well-known newspaper. This advert will show easy ways of taking action to protect the climate and thus possibly avoid dangerous climate change. The more money is collected, the bigger and conspicuous the advert becomes. If this action succeeds, sponsors for international advertising campaigns could be enticed.
After reading this text completely, please confirm by pressing the OK-button.
Professor Jochem Marotzke, Director of the MPI for Meteorology in Hamburg will write a short treatise on the current state of the global climate, and then make some suggestions on how to reduce the CO2-emissions and thus to protect the climate.
For example, energy can be saved by reducing the room temperature in winter by a couple of degrees at home or by more frequent use of public transport instead of private cars. The intense use of regenerative energy sources also helps in reducing CO2-emission.
After reading this text completely, please confirm by pressing the OK-button.
Information on climate rounds - continued
After each round all decisions will be shown to all players.
Example:
In this case 4 players decided to invest into climate protection.
Of these 4 players, 2 decided to invest 2 Euros each, and the other 2 decided to invest 4 Euros each.
Name of the player / Leda / Triton / Portia / Sinope / Carpo / GalateaDecision / Yes / No / No / Yes / Yes / Yes
Change of players account / -2,00 / 0,00 / 0,00 / -4,00 / -2,00 / -4,00
In total 12 Euros were invested into climate protection and thus added to the climate account.
After reading this text completely, please confirm by pressing the OK-button.
The end of the game
At the end of the game (exactly after 10 rounds) the computer will compare the money in the account to a predefined amount (120 Euros). This amount would have to be collected to prevent dangerous climate change. The amount will be reached if every player pays 2 Euros into the climate protection in each round on average. In this case 12 Euros would be paid into the climate account per round.
If this amount has been reached in the climate account, each player receives her/his endowment of 60 and 30 Euros, respectively, anonymously paid in cash, together with the money out of his/her operating fund that has not been invested.
If this amount has not been assembled in the climate account, dangerous climate change with significant economic losses will occur with a probability of 90% (this means in 9 of 10 cases).
With this probability you will lose your endowment of 60 and 30 Euros, respectively.
The money from your operating fund that you did not invest will be paid anonymously to you in cash anyhow.
(There is a probability of 10% (this means 1 of 10 cases) that you retain your endowment, which you will receive anonymously together with the money from your operating fund that you had not invested, in cash.)
The computer will randomly calculate the result with the corresponding probability.
After reading this text completely, please confirm by pressing the OK-button.
Climate event
If after 5 rounds the group has not succeeded in reaching the intermediate target of 60 Euros paid into the climate protection account, the following rounds 6 – 10 will each have a climate event (i.e. flood, storm, etc.) with a probability of 20% per round, which means in 1 of 5 cases. As this is the case for each of the last five rounds, each group will be hit at least once by an event on average. It might not happen at all or it can happen two or three times,(however, this is less likely). At the start of each round (rounds 6 – 10) you will be informed if a climate event has taken place.
Each time a group is hit by a climate event your operating fund as well as your endowment will be reduced by 10%. 10% means that a “rich” player loses 4 Euros from her/his operating fund and 6 Euros from his/her endowment. A “poor” player loses 2 Euros from his/her operating fund and 3 Euros from her/his endowment. This money is ultimately lost.
Please note that this means that you have less money at your disposal to achieve the final target of at least 120 Euros after round 10.
If your group has reached the intermediate target of at least 60 Euros in the climate protection account by the end of round 5, there will be no climate event in any of the following rounds.
After reading this text completely, please confirm by pressing the OK-button.
Operating fund, 40 and 20 Euros, respectively:
This can be used to pay into the climate account during the course of the game. The money that you do not invest or lose through a climate event will be paid to you anonymously at the end of the game (regardless of whether your group achieved the target of at least 120 Euros in the climate account).
Endowment, 60 and 30 Euros, respectively:
You will receive the money anonymously in cash (potentially reduced by losses as a result of climate events) if the group paid at least 120 Euros into the climate account.
If your group did not achieve the target of 120 Euros you will lose your endowment with a probability of 90% (in 9 of 10 cases).
“rich” (operating fund 40 Euros, endowment 60 Euros) are:Ananke, Telesto, Despina
“poor” (operating fund 20 Euros, endowment 30 Euros) are:Japetus, Kallisto, Metis
After reading this text completely, please confirm by pressing the OK-button.
The experiment starts now!
After reading this text completely, please confirm by pressing the OK-button.