Tragedy of the commons
The depletion of a shared resource when each user gains from taking more while the damage is spread across everyone.
Example
Open-access fisheries and the atmosphere's limited capacity to absorb CO₂ are common examples.
The catch
Studies of community-managed resources show depletion is avoidable where users can set and enforce shared rules.
In more depth
Tragedy of the commons, explained.
The tragedy of the commons describes open access, where nobody can exclude anyone, and that distinction shapes the remedies. The atmosphere is the hardest case, because its users include every country and generations not yet born.
Climate policy answers the problem with tools that limit or price access. A cap-and-trade scheme such as the EU Emissions Trading System turns the right to emit into a limited supply of allowances, while taxes attach a cost to each tonne. International agreements depend on shared measurement and disclosure, because rules that users cannot check tend to fail. The closely related free-rider problem explains why each country hesitates to pay for protection the others enjoy.