Given the increasing maps of above-ground biomass, an essential climate variable, it is important to assess them with respect to the map user requirements. Map assessment requires uncertainty assessment not only from the maps, but also from the reference data used. This PhD project aims to assess biomass and biomass changes at global scales under an uncertainty framework and for the benefit of map users and even producers. The project also aims to demonstrate country cases that make use of the assessed global biomass products particularly for (1) carbon accounting in the context of National Ecosystem Accounting and (2) near-real time carbon emissions monitoring in the context of REDD+ Monitoring, Reporting, and Verification.