An IPCC Special Report on Carbon dioxide Capture and Storage reveals another example of such an approach in the “tonne-year alternative for accounting” that defines an artificial equivalence so that capture and storage for a given time interval (for example, t years) are equated with permanent storage. Typically capture and storage for one year would result in a number of credits equal to 1/t, and thus storage for t years would result in one full credit. A variety of constructs have been proposed for defining the number of storage years that would be equated with permanent storage. “Despite being based on scientific and technical considerations, this equivalence is basically a political decision.”
 IPCC Working Group III, Mitigation of Climate Change, Carbon Dioxide Capture and Storage.