The Marrakesh Accords require each Annex I Party to have in place a national system to estimate its greenhouse gas emissions and removals, along with a national registry to account for, record, and monitor transactions in AAUs, ERUs, CERs and RMUs.

Prior to the start of the commitment period, each Annex I Party must submit a report to the secretariat describing its national system and registry, and providing the emissions data necessary to formally establish its assigned amount. To establish their assigned amounts, Annex I Parties need to make a number of choices, for example, whether to use 1990 or 1995 as a baseline for their emissions of HFCs, PFCs and SF6, and which tree height value to use to define a forest.

Assuming no questions are raised by the expert review teams who will review the reports, the assigned amount of each Annex I Party is then recorded in a compilation and accounting database held with the secretariat. This database will record the annual emissions of Parties (as reported in their annual inventories  see below), along with their total annual transactions in AAUs, CERs, ERUs and RMUs. These reports will be forwarded to the COP/MOP and the Compliance Committee.

As an added monitoring tool, the secretariat will manage an independent transaction log, which will automatically check the validity of transactions under the flexibility mechanisms and LULUCF activities. Every year, the secretariat will publish a compilation and accounting report for each Annex I Party, based on the information contained in its database. The final secretariat report published at the end of the commitment period will form the basis for assessing whether Annex I Parties have complied with their emission targets.