http://earth2tech.com/2008/03/25/the-network-effect-on-carbon-footprints/

The rising levels of CO2 may prove to be the biggest problem with the world today.  This article discusses attempts to use network effects to lower the “carbon footprint” of ordinary people.  The idea is that if data on each person’s “carbon footprint” is made available to the public, people will be increasingly more aware of their carbon usage and strive to lower this number in order to appear better to their friends.  The article mentions research which shows that if the average electric bill of their neighbors is known, people will tend to change their usage to be closer to the average.  The Facebook application Carbon Minder is an example of this idea that’s already been implemented.  When you add Carbon Minder on Facebook, you can see your carbon footprint in relation to the average of your network and your friends.

One potential problem with this scheme is that it really needs to reach a large audience in order to have an impact.  Without this carbon footprint being somehow mandated to be public information, people will just not share their carbon footprint if they know it is large.  It would require a large fraction of Facebook users to get the application in order to “force” these people to join.  With a large population, people could be viewed negatively for simply not having the application and “fessing up” to their footprint.  With only a small population, a negative judgment cannot be made because the person may just be naive about the existence of the application.