Why fNRB is key for cookstove and household carbon projects

Tuesday, 30 Jan 2024

Calyx Global assesses the greenhouse gas (GHG) claims of energy-efficient and fuel-switch cookstoves, alongside domestic biodigester projects. A key parameter in calculating emission reductions for projects that aim to reduce the consumption of unsustainable biomass for thermal energy is the fraction of non-renewable biomass (fNRB), which represents the proportion of wood harvested that exceeds the regeneration rate of a given area. As such, fNRB is a core component for determining baseline emissions, and associated emission reduction claims, for projects involving the dissemination of cookstoves and/or household biodigesters. 

Around 2.3 billion people utilize solid biomass for cooking worldwide. In areas where people rely heavily on biomass for fuel, the tree cover may diminish, resulting in landscape degradation and potentially contributing to long-term deforestation. Biomass fuel can be considered renewable if the original source of the fuel regrows at least at the same rate that it is harvested. However, when more wood is harvested than replenished in the landscape, it leads to unsustainable harvesting[1]. 

Currently, the fraction of non-renewable biomass is defined by the carbon project proponent and should, in principle, be conservative due to the need to make several assumptions in its calculation. The principle of conservativeness in carbon markets refers to erring on the side of caution to ensure emission reductions or removals are unlikely to be overestimated[2]. Currently, project developers have three basic options when determining the value of fNRB to be used in a project, in most commonly applied methodologies:

(a) Using a default value of 0.3 (30%);
(b) Using pre-approved default country-specific values, known as standardized baselines, where available; or
(c) Calculating project-specific fNRB values using TOOL 30 guidelines.

The use of the universal default value of 0.3 (30%) is a relatively recent addition to this option list and has seldom been applied in Clean Development Mechanism (CDM) projects and Programme of Activities (PoAs) and other carbon programs of the voluntary carbon market (VCM). Instead, most projects use one of the two latter options, which typically yield higher fNRB values, corresponding with higher emission reduction claims.

To evaluate the risk of over-crediting based on the overestimation of fNRB, Calyx Global compares the fNRB value applied by the project to benchmark values. Where possible, we compare project fNRB values with values that are based on spatial models that consider woodfuel and charcoal demand, woody biomass regrowth rates, and geographical, ecological and land use heterogeneity, such as the WISDOM model[3], or the more recent MoFUSS model (introduced below) that also simulates landscape changes over time[4]. We evaluate the project’s fNRB value against the results from the most recent published literature for the project’s specific location.

In the first week of October 2023, the CDM Methodologic Panel published preliminary results from MoFUSS modeling. The model itself is peer-reviewed[4] and the values derived are under UNFCCC public consultation and further review. These preliminary values represent up-to-date and independently determined fNRB data; as such, Calyx Global has begun to incorporate them into our ratings.

This research, supported by the United Nations Framework Convention on Climate Change (UNFCCC), currently provides fNRB values for 43 sub-Saharan countries and their regional estimates where applicable. A new set of updated fNRB values is expected to be published for most developing countries worldwide, including those covered in the pan-tropical WISDOM study of woodfuel sustainability[3]. Both WISDOM and MoFuSS serve as principal reference points in the effort to gather fNRB estimations.

We recognize that fNRB values may change during the review process, and we acknowledge the difficulties involved in estimating fNRB. To the best of our knowledge, MoFUSS represents the most updated and comprehensive tool to analyze this variable. Stay tuned for a more detailed paper that takes a deeper dive into fNRB, where we further explain the parameter, analyze its historical application, and explain the specificities of CDM Tool 30 and MoFUSS.

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[1] UNFCC (2023). CDM-MP92-A07 Information note: Development of default values for fraction of non-renewable biomass.

[2]  ICVCM. (2022). Consulting on the Core Carbon Principles Part 5: Terms & Definitions. The Integrity Council for the Voluntary Carbon Market. ICVCM-Public-Consultation-FINAL-Part-5.pdf

[3] Bailis, R., Drigo, R., Ghilardi, A. & Masera, O. (2015). The carbon footprint of traditional woodfuels. Nat. Clim. Change 5, 266–272; Bailis, R., Wang, Y., Drigo, R., Ghilardi, A. & Masera, O. (2017) Getting the numbers right: Revisiting woodfuel sustainability in the developing world. Environ. Res. Lett. 12.

[4] Ghilardi, A., Bailis, R., Mas, JF., Skutsch, M., Elvir, JA., Quevedo, A., Masera, O., Dwivedi, P., Drigo, R., Vega, E. (2016). Spatiotemporal modeling of fuelwood environmental impacts: Towards improved accounting for non-renewable biomass. Environmental Modelling & Software, 82, 241-254. Spatiotemporal modeling of fuelwood environmental impacts: Towards improved accounting for non-renewable biomass - ScienceDirect


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Calyx Global

This article includes insights and input from multiple experts in Calyx Global.