CO₂ Removal by Sinking of Terrestrial Biomass
CO₂ Removal by Sinking of Terrestrial Biomass can be quantified as:
Where:
Calculated based on the total mass of carbon buoys loaded onto a specific deployment vessel, the portion of buoys composed of terrestrial biomass, the moisture content of biomass at the time of loading, and the carbon content of ‘bone dry’ biomass.
Quantified via a combination of direct measurement of mass of material used in buoys and a standard conversion factor for carbon content of material based on species used. Terrestrial biomass is sampled and submitted to a partner lab for analysis of moisture content, carbon content, and ash content.
A small amount of loss may be observed during transport due to high winds and waves.
For initial deployments off of barges, loss is estimated by comparing time lapse camera image analysis to total volume calculated from barge dimensions and loaded height measurement.
In the event of camera issues or unexpected weather events, additional conservative discount factors may be applied.
Laboratory experiments are conducted to measure remineralization rates, sinking rates, and the amount of organic compounds leached, dissolved, or otherwise separated during the flotation time of terrestrial biomass (including particulate organic carbon and dissolved organic carbon such as organic acids).
Direct observation of biomass loss via in-situ image analysis from observational camera systems further informs and refines float times.
Conservative estimates of terrestrial biomass separation during floating periods outside of eligible sinking locations are applied.
Spatial evolution of the carbon buoy population is evaluated across quantification approaches:
Carbon buoy sinking speed is evaluated in laboratory and coastal settings.
Lateral transport of carbon buoys during sinking can be modeled using publicly available ocean current models. These models resolve subsurface ocean currents at various depths, and are validated against in-situ data. Such models can be used to quantify the maximum horizontal distance that a carbon buoy may travel during its descent given a particular .
Modeling and laboratory results can be further supported via direct measurement from GPS sensor buoys.
. Models start with initial distribution of passive floating points (carbon buoys), simulate floating trajectories, and then simulate sinking to the terminal location on the seafloor. The time that carbon buoys sink is simulated using the float time distributions described above and trajectories defined by the interplay between wind, waves and currents. Thousands of simulations are run to determine the probability curve within the range of possible values. The results of these model runs produce a final probability plot of terminal carbon buoy distribution on the seafloor, which defines a single variable output with a given confidence level.
Beyond initial deployments, additional in-situ observations of sinking rate — including the use of submersible AUVs to follow deployments throughout surface drifting and eventual sinking to the seafloor — are planned and expected in the coming years. Benthic research programs with external oceanographic collaborators are currently being finalized.
Actual depth in shallower locations may be of less importance than sedimentation and remineralization rates, as the percentage of organic carbon preservation varies with total sedimentation rate (i.e. the faster something is buried, the more likely its carbon will be preserved in its organic form). Similarly, benthic research programs will be needed to inform expected biomass burial and remineralization rates.
Related to the additionality of project activities. Effective drawdown from terrestrial biomass sinking occurs so long as the biomass would not have otherwise been moved into the slow cycle (certain types of biochar applications, biomass burial, bio-oil injection, etc.) and does not negatively impact the net carbon stock of the .
With a fast-to-slow framing for terrestrial biomass, the primary consideration is the stability of the carbon reservoir in question. Carbon stored in aboveground biomass, whether in short-lived industrial processes, a managed forest, or subject to natural decay, is inherently volatile and subject to a high risk of reversal, meaning that the carbon contained within this biomass may move between fast cycle reservoirs in a matter of months, years, or decades. As such, the removal activity related to this biomass occurs when that potential volatility is eliminated. Aboveground biomass and surface soils are thus functionally fast systems that will largely remain in the fast cycle (in their baseline state, as atmospheric CO₂ or as dissolved CO₂ in the surface ocean) via soil/root respiration or decomposer respiration from dead wood/leaves. Conversely, the underlying “stable” soil carbon layer is functionally a slow cycle reservoir in that the carbon contained is unlikely to move into a different reservoir without human disruption or significant land use change.
While this framing implies that all aboveground terrestrial biomass could potentially be additional from a purely carbon accounting perspective, practically speaking, the management of aboveground biomass and surface soils will impact both fast cycle carbon fluxes and the stability of the underlying stable soil layer, along with critical non-carbon secondary effects on biodiversity, ecosystem health including watershed benefits and oxygen production, and more. As such, biomass eligibility and sourcing considerations are determined not just by fast and slow carbon cycling, but also by their potential impact (positive and negative) on the above secondary effects and fast cycle fluxes.
For residue sources, this is straightforward; differentiating between materials that would be burned versus left to decay is de minimis, as GHG Protocol guidance for dead organic material states that the timing delay associated with baseline CO₂ emissions from degradation does not require amortization and can be claimed at the time of intervention. Supplier attestations on the alternative baseline state of sourced residue biomass are required to demonstrate additionality.
For biomass sourced from non-residue origins, biomass obtained through sustainable forest management shall be utilized, and on a long-term basis, “purpose-grown feedstock” — i.e. terrestrial biomass that is grown on marginal or arid land for the explicit purpose of biomass-based carbon removal — will be considered, contingent on their impact on secondary effects.
Biomass sourcing standards will need to continue to be developed and adopted at an industry level, especially as competition for available biomass is expected to increase.
Related to the impact on the net carbon stock from land use change due to project activities, and encompassing the harvesting of terrestrial biomass leading directly to emissions elsewhere (i.e., leakage). Supplier attestations for all biomass sources will be required, and any additional emissions that directly result from increased demand for biomass will be monitored and included in the calculation of net carbon removed.
For residues, all biomass sourced is FSC certified and sourced from FSC Forest Management Certified suppliers, or from an equivalent certification system in the event FSC is not in use in a given jurisdiction or with a given species. Low-grade biomass resources are currently in abundant supply, in part due to economic shifts in the demand for materials such as low-grade pulp wood, along with readily available materials such as sawmill cut offs and wildfire management burn piles.
Land use change modeling will follow GHG Protocol best practices and industry standards specific to . Notably, existing land use change models are atmospheric-centric in their design, and as such early deployments are likely to be inherently conservative in their accounting for potential fast cycle fluctuations.
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