Isn’t the comparison made in the Kyoto Protocol between emissions at a point in time and 1990?
Not in the case of the sector called “land use, land-use change and forestry” (LULUCF, pronounced “loo-loo-sea-eff”), which is the sector that applies to DOC.
1990 is the benchmark year for deciding whether a piece of land is covered in existing forest, (which would be a matter of “forest management” under the Kyoto Protocol) or if it’s land that is new forest since 1990 (a matter of “afforestation”).
It’s much easier to measure the carbon storage of a forest at points in time and compare the results, than try to measure all carbon fluxes over time. Also, it would be difficult to find out what the carbon storage in existing forests was in 1990. The best that can be done is to compare the carbon storage in 2017, say, with that in 2013, and that’s how the Kyoto Protocol works.