Policy and Complex Systems
Looking at situations evolving toward sustainability , we can observe , as the Sustainability Tipping Point ( STP ) is reached much earlier than the overall Reduction Goal ( RG ). In Fig . 5 for example we can observe as the RG is reached after 300 runs , while the STP is reached only after about 80 runs .
If we can consider the reaching of the RG as a long-term effect of a sustainability social norm , STP could be seen as an “ early warning ” signal , able to anticipate the reaching of sustainability . An interesting property of SAM4SN would rely on considering the STP as a sustainability real-time indicator .
Robustness of the model
The statistical robustness is quite implicit , due to the construction of the model , being the unique source of variability the space localization of the agents . In each case here the results are related to small changes in agents ’ attitude , the soundness has been verified repeating the simulation one hundred times . Two extreme cases are reported , where the system behave in a completely different way changing the attitudes of a unique agent of about three hundreds . In the first of the two cases we measured 0 different results and for the other one 14 % of different outcomes . With large actual sample of agents with their real data and geographical location , the outcome – after one year of simulated behavior –, are consistent with ex post real data .
Sustainability Tipping Point as indicator
An indicator is a measure that is used to demonstrate change in a situation , or the progress in , or results of , an activity , project , or program . STP could be considered as a qualitative monitoring indicator .
An indicator is a useful tool if it is reliable . To demonstrate if the STP is a reliable indicator we have to demonstrate four conditions .
• The STP becomes always true when the system leads to sustainability .
• The STP becomes true always before the reaching of the sustainable state .
• The STP stays always false when the resource consumption trend is unsustainable .
• The STP becomes true only once .
We performed three sets of experiments to demonstrate these conditions . Each set is composed by 81 experiments .
The configurations of each set of experiments depend on the initial number of different types of agent and on the configuration of the smart metering functions , that impact on consumption patterns : simple metering availability and neighbor comparison affect the individual reduction goal , while feedback and suggestion affect the rate to reach such a reduction . The availability of one or more smart metering functions facilitates the reaching of sustainability .
We performed such three sets of experiments using NetLogo BehaviorSpace utility . We set as “ time limit ” for the experiment that the simulation stops after 800 runs , if the reduction goal is not reached before . For more details , you can see Sissa ( 2014 ).
We observed the results of the three sets of experiments , in order to verify the four conditions required to consider the STP a reliable indicator .
We recorded the run when the STP becomes true and we call it STP .
59