Moving to higher tiers for soil carbon

The 2023 revised LULUCF regulation will require Tier 2 methods for monitoring all land and carbon pools by the reporting of the 2026 emission year, and then later Tier 3 methods for a subset of land including, among others, forests and peatlands that undergo restoration or protection for nature directives. This requirement is particularly challenging for soil carbon for which Tier 1 is still used by many Member States for several land categories. This document offers answers to frequently arising questions in the topic of higher methodological tiers for soil carbon pool monitoring, as well as practical advice on how to implement them. Regarding Tier 2, we suggest a step by step method to estimate reference carbon stock (SOCref) and carbon stock modifying factors (eg. FLU) using national datasets on soil carbon or international databases such as the LUCAS soil survey. We also propose a list of FMG emission factors for agricultural practices based on a literature review for the temperate zone. Regarding Tier 3, we distinguish between measurement-based methods (repeated soil inventories) and model-based methods. Measurement-based methods tend to be costly, but they are necessary as no model can guarantee an accurate national total in a context of environmental and management changes. Model-based methods allow to disentangle the different drivers of soil carbon changes and reduce the number of repeated measurements needed. Their evaluation, in line with the IPCC guidelines, is also discussed.