Imagine you are lord of the manor in feudal times, and you have provided a large pasture (the commons) for your serfs to run their cattle. Of course, each serf family wants to increase its herd to better themselves, and before long, there are too many cows and the common is overgrazed, turning the field into an eroded area unfit for anything.
The lord of the manor has two choices. He can decree that each family can only run a certain number of cows, or he can divide and fence the commons into individual plots where each family will bear the cost of overgrazing its own plot.
But suppose the commons cannot be divided, as the air, water, climate and fisheries on earth cannot be divided. And suppose there is no lord to make and enforce the rules? That is exactly our global predicament. We have 200, more or less, sovereign nations all competing to maximize the planet’s resources, especially the atmosphere.
Fortunately, there is a third option. The serfs, in our case the nations, can come together and agree on the equitable use of the common resource. That is exactly what the Paris accord is all about.
It just so happens that this latter method honors the core ethic of all the world’s major religions: “Love thy neighbor as thyself.” (Credit to Garrett Harden who wrote “The Tragedy of the Commons” published in 1968.)