Tier levels

Methods to estimate GHG emissions and removals can vary significantly regarding the level of complexity. The IPCC Guidelines refer to different “Tier levels” ranging from the use of global default values and international statistics (Tier 1) to the use of country specific data (Tier 2) and advanced methods based on data from field measurements and modelling (Tier 3).

Using higher Tier methods improves the accuracy and usefulness of land sector GHG reporting by capturing the effects of detailed management practices, distinguishing policy and natural impacts, enabling projections for multiple policy purposes, and providing broader insights despite requiring more data and assumptions.

The LULUCF Regulation requires that Member States prepare high-quality, accurate GHG inventories. Currently 15% of reported emissions and removals in the EU are estimated using a Tier 1 methodology. Tier 2 methodologies account for 62% and Tier 3 methodologies for 23% (NIDs for 2023). How to advance methodologies towards the integration of more national data and the use of detailed measurements and modelling depends on data being available and data infrastructure, but also the capabilities of the reporting systems used to incorporate better data.

What are Tier levels?

Tier levels refer to the methodological complexity used to estimate GHG emissions and removals. The IPCC provides three tiers, increasing in detail, data needs and accuracy:

Tier 1 methods use readily available statistical data and default emission factors from the IPCC Guidelines. Tier 1 emission factors also assume typical processes on land areas for certain regions. This method is often not very accurate for emissions and removals from land use and land use changes.
Tier 2 methods are similar to Tier 1 in terms of methodologies, but default emission factors are replaced with country-specific emission factors. These are being developed on the basis of knowledge of the types of processes and specific conditions that apply in the country for which the inventory is being developed. This method should lead to an improvement of estimates over Tier 1 because default values proposed for Tier 1 are based on a large spectrum of references that are not always representative for individual Member States.
Tier 3 methods are more complex, they encompass country-specific methodologies with high resolution. Tier 3 methods can entail repeated measurement campaigns (e.g. National Forest Inventories) or specific modelling approaches calibrated and validated for the country against measurements (e.g. biomass models). If properly validated, the modelling method will lead to an improvement of estimates over Tier 1 and 2 because it better reflects the temporal dynamics and fills data gaps that exist at lower-level methods.

Figure 1: Example of methods by Tier level, land use and pool

What does the LULUCF Regulation say?

The LULUCF Regulation requires that Member States prepare high-quality, accurate GHG inventories. From 2021, all categories shall be reported with at least Tier 1 methodologies, and Tier 2 methodologies for key .

From the 2028 GHGI submission onwards, the LULUCF Regulation requires the application of at least Tier 2 methods for all managed land categories and emission sources.

From the 2030 submission onwards, the LULUCF Regulation requires the application of Tier 3 methods for most forest land, grassland, and wetlands.

Learn more about post 2030 requirements

From the 2030 submission onwards, estimating carbon fluxes from the following land areas will require Tier 3 methods for all carbon pools:

Land use units with high carbon stocks, in particular areas of undrained wetlands, forests and wooded lands
Land use units under protection, restoration or identified in need of restoration, especially areas with high biodiversity value including primary forests, species-rich natural forests and wooded lands, protected areas, natural grasslands and species-rich grasslands, sites under the Habitats Directive, the Birds Directive, the Water Framework Directive, and the Floods Directive.
Land use units facing high future climate risks, especially areas affected by natural disturbances and areas identified with high risks and subject to climate-related disaster reduction actions in the national adaptation strategy of Member States.

The comprehensive list of area definitions is provided in the Governance Regulation (Annex V, Part 3) amended by Regulation 2023/839.

The consideration of these criteria indicates that a large area of land will require Tier 3 methods. Substantial areas meeting these criteria (e.g. undrained wetlands) are currently considered as ‘unmanaged’ under UNFCCC reporting and their GHG emissions and removals are therefore not estimated. The Regulation still allows not to report the emissions and removals in unmanaged land.

Nevertheless, if a Member State applies Tier 3 methods for a reporting category (e.g. forest land remaining forest land), the requirement will be fulfilled for land areas included in these categories too. Moreover, if land areas represent less than 1% of managed land reported by a Member State, Tier 2 methods are sufficient.

Member States are especially encouraged to use advanced technologies available under EU programs, such as Copernicus, and national high-quality data. A list of relevant geospatial data for LULUCF, including Copernicus products, can be found on the Data Catalogue.

How to move to higher Tiers?

Moving to higher Tiers will represent a different challenge for each Member State depending on the current state of their GHG inventory. Indeed, there is a wide disparity between the use of methodologies by EU countries. The use of Tier 3 methods covers about a quarter of all reported emissions and removals and is attributed to just a handful of countries. A significant proportion of land and carbon pools is still covered by inventories using a Tier 1 methodology. Based on the state of inventories in 2025 (Chapter 2 of the EEA report Enhancing Europe's land carbon sink), the most challenging issues on Tier levels are expected for the following cases:

Emissions and removals on mineral soils

Emissions and removals on organic soils

Emissions and removals of biomass on cropland and grassland

Emissions and removals on wetlands

Emissions and removals on settlements or other lands

Non-CO2 emissions

Emissions from biomass burning

Wildfires are increasing in frequency and severity across Europe and are becoming a more significant component of the LULUCF GHG balance. Reporting is dominated by Tier 1 and Tier 2 approaches, combining IPCC default emissions and combustion factors with national activity data (mainly burnt area and biomass stocks). Only a limited number of MS apply higher Tiers or fire-event specific approaches.

You may also be interested in viewing the related EEA webinar on: GHG emissions from Biomass burning: status and options for improvement

Use of models

Tier 3 approaches include model-based methods that are able to describe carbon transfers between different carbon pools. For the soil carbon pool, for example, they may simulate soil carbon changes based on site conditions and carbon inputs such as weather data, soil type, and litter input (which is derived, for example, from forest inventory and harvest statistics data). Note that models can be simple and yet allow for policy-relevant reporting, as long as they can be calibrated and verified using reliable and representative national data.

There are a number of models already used by EU Member States for GHG reporting in the LULUCF sector. The Czech Republic, Ireland, Romania, Poland, and Slovenia apply the empirical Carbon Budget Model (CBM-CFS3) in forest land, originally developed for the Canadian forestry sector. The CBM-CFS model uses yield-table data and simulated the carbon dynamics of above-and belowground biomass, deadwood, litter and mineral soil at stand and landscape level (Kurz et al. 2009).

The most commonly used model for describing changes in soil organic carbon (SOC) stocks is Yasso (Liski et al. 2005), which is applied in Austria, Finland, Norway, and Germany for estimating SOC in forest land. In Finland, Yasso is also applied to cropland and grassland. The model CTOOL is applied in Denmark for cropland and grassland, whereas ICBMregion is used in Sweden and RothC is used in the Netherlands for the cropland category.

You may also be interested in viewing the related EEA webinar on: Soil GHGs in LULUCF: status and options for improvement

How to ensure time-series consistency when moving to higher Tiers?

A common worry when moving to higher Tiers is to ensure time-series consistency. Chapter 5 of Volume 1 of the IPCC Guidelines provides a list of pragmatic techniques and concrete examples on how to ensure time-series consistency, including overlapping, use of surrogate data, interpolation, trend extrapolation, and non-linear trend analysis. It also leaves room for "other techniques" when none of the techniques above can be satisfactory implemented.

A calibration approach is describes in the case study "Combination of data and a simple model to increase time resolution in the French inventory" for France, where data with high accuracy but low temporal resolution (forest inventories) and data with high temporal resolution but lower accuracy (harvest statistics) are combined.