Timing issues involve the dynamics of emissions and removals, issues of duration (including ton-year accounting and risk), and time preference.
The inherent asymmetry in the timing of carbon emissions versus removals in biotic systems creates difficulties in initializing a carbon accounting system. Consider a forest that is managed for steady-state carbon stocks using a 100-year rotation. In any given year after the first century of management, 1 percent of the forest is logged while regrowth occurs in the other 99 percent of the forest area. In the area where logging occurs, most of the aboveground biomass carbon is immediately released or removed from the site. At that particular location, full recovery of the stock of biomass carbon will take 99 years. The carbon stock of the forest biomass as a whole remains constant, however, because regrowth is occurring throughout the rest of the forest. An accounting system that has been operating indefinitely will appropriately show zero net emissions or removals whether it treats the entire forest as a single unit or separately accounts for logging and regrowth. If, however, the accounting system only includes activities taking place after a given date, such as 1990, separate accounting of logging and regrowth would lead to reporting of net emissions because the emissions would be almost fully accounted for, but only a portion of the regrowth would be included. Conversely, if logging occurs periodically rather than on a continuous basis, net uptake of carbon could be reported under the accounting system if no logging happens to occur during the commitment period. The potential for accounting artifacts from these timing differences is a key issue that can be addressed through the definitions adopted for implementing Article 3.3 (see Chapter 3) and the approach to additional activities adopted under Article 3.4 (see Section 4.6).
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