Biochar As A Carbon Sequestration Mechanism: Decomposition, Modelling, And Policy
Bibliographic record
Abstract
Black carbon, or biochar (BC), has a strong but complex potential as a tool for climate change mitigation, due to its high carbon (C) stability, through its application within specific biomass management systems, and depending on the policy tools necessary to establish it effectively within climate change mitigation projects. The term "black carbon" encompasses a spectrum of materials produced during incomplete combustion, including soot and charcoal, while "biochar" is used to distinguish the material from charcoal created for fuel, and to denote its particular application in C sequestration and emission-reducing projects as a soil amendment. Understanding the influence of production temperature, feedstock, and other initial properties on BC stability is critical for evaluating or managing terrestrial C stocks. This thesis quantifies C loss in BCs produced at 7 different temperatures from 6 different feedstocks as well as the original materials through a 3-year microbial incubation in sand matrices. Carbon losses are interpreted using a number of properties, including Fourier-transformed infra-red spectra. High temperature BCs were characterized by lower volatile and higher fixed C contents and the increasing dominance of aromatic C compounds in increasingly condensed forms. 300°C BCs lost 17.8% more C than 600°C BCs, which did not show significant C losses. It was found that production temperature has a greater influence on 3-year C stability than feedstock, likely due to the different temperature ranges at which different organic compounds are modified by heating. However, the C debt or credit ratio, which takes into account the C losses from the original feedstock that are incurred upon charring, is highly sensitive to feedstock type. Corn BCs attained ratios of 2.29-2.81, while no oak or pine chars reached the "break-even ratio" of 1 after 3 years. The introduction of cook stoves that produce BC as well as heat for cooking into small farm households in western Kenya is an example of a specific system in which BC production could be applied. System dynamics modelling was used to: (i) investigate the climate change impact of prototype and refined BC-producing pyrolytic cook stoves and improved combustion cook stoves in comparison to conventional cook stoves; (ii) assess the relative sensitivity of the stoves to key parameters; (iii) quantify the effects of different climate change impact accounting decisions. Simulated reductions in greenhouse gas (GHG) impact from a traditional 3stone cook stove baseline range between 2.56-4.63 tCO2e/household/year for an improved combustion stove and 2.58-5.80 tCO2e/household/year for the pyrolytic stoves, of which BC directly accounts for 14-50%. The magnitude of these reductions is about twice as sensitive to baseline wood fuel use and the fraction of non-renewable biomass (fNRB) of off-farm wood that is used as fuel as to farm age/soil degradation status or stability of biochar. Reductions in GHG impact decrease if a household must access non-renewable fuel sources. Stoves with higher wood demand are less sensitive to changes in baseline fuel use and rely on biochar for a greater proportion of their reductions. This thesis investigates policy and methodology aspects of BC systems used for carbon management, including the criteria for establishing additionality, baselines, permanence, leakage, system drivers, measurement, verification, economics, and development for successful stand-alone projects and carbon offsets. Findings include that applying baselines of biomass decomposition rather than total soil carbon is effective and supports a longer crediting period than is currently standard. Explicitly designing a BC system around "true wastes" as feedstocks combined with safe system drivers could minimize unwanted land-use impacts and leakage With biochar production introduced into bioenergy systems, under a renewable biomass scenario, the change in emissions increases with higher fuel use, rather than decreasing. Integrating these findings with system-specific analysis and an increased understanding of C stability in BCs should inform the design of effective applied BC systems.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".