Anyone who has tried to enter and understand the world of international forest carbon accounting has come across the terms 'gross-net' and 'net-net'. Many have been totally confused; others have thought they understood but don't. Here is the simplest explanation you'll find (let's hope I'm right):
In these terms are two word positions, for example in 'gross-net', 'gross' is in the first position and 'net' in the second. Knowing what these two positions refer to is the key to understanding these two terms.
The second position refers to whether total carbon fluxes are measured, i.e. both emissions and removals. If only emissions were measured, it would be 'gross' accounting. Since in both cases, emissions and removals in the commitment period are added together to get a total carbon flux, 'net' appears in the second position of both terms.
The first position refers to whether or not the carbon flux in the commitment period is compared to the carbon flux in a base year. In this case, 'gross' means the total carbon flux is used and it is not compared to the base year carbon flux; 'net' means that the carbon flux in the commitment period is compared to the carbon flux in the base year - the base year carbon flux is subtracted from the carbon flux in the commitment period to give you a net change.
'Gross-net' = total carbon flux in the commitment period.
'Net-net' = carbon flux in the commitment period minus carbon flux in the base year.
Simple, right? :)