Biochar systems for carbon finance -- an evaluation based on Life Cycle Assessment studies in New Zealand : a thesis presented in partial fulfilment of the requirements of Doctor of Philosophy in Science at Massey University, Wellington, New Zealand
Char produced from the pyrolysis of biomass and applied into soils (biochar) can, under some conditions, improve soil functions and sequester carbon (C) over millennia. In New Zealand, if 80% of the available biomass residues were converted into biochar, about 1.7 Mt CO2 could be sequestered annually. This represents ~2.4% of NZ’s total annual greenhouse gas (GHG) emissions. However, the trade-offs associated with alternative uses of biomass need to be assessed from a life cycle perspective, particularly when considering policymaking.
The biomass feedstocks evaluated using Life Cycle Assessment were orchard prunings, logging residues, and wheat straw. The goals were i) to compare alternative management scenarios and ii) to determine the use of biomass that can achieve the largest amount of carbon credits in order to support policymaking. The biomass for heat-only (HO) scenario could mitigate 276 – 1,064 kg CO2-eq per t biomass; the combined heat and power (CHP) scenario could reduce 410 – 1,608 kg CO2-eq per t biomass; and the biochar scenario could abate 271 – 792 kg CO2-eq per t biomass. Ranges vary according to the type of feedstock assessed and the type of fossil fuel (coal or natural gas) displaced. The assessment of the HO and CHP systems giving greater GHG emission reductions than the biochar system can be misleading as these only involve fossil-fuel offsetting whereas the biochar system would sequester some carbon irrespective of the other activities assumed to be displaced. The biochar carbon stability factor is the key component that affects its capacity to mitigate climate change. A distinctive C accounting, reporting and crediting approach should be developed for biochar to have high economic potential in carbon-pricing mechanisms.
Several approaches for incentivising biochar carbon sequestration were explored. These include using conservative carbon-accounting estimates, issuing temporary credits, establishing buffer funds, creating carbon credit multipliers, and inventing a new unit such as ppm CO2 reductions for recognising atmospheric CO2 removals as opposed to avoiding GHG emissions. While biochar technology is currently facing numerous barriers for acceptance in carbon markets, its future is promising since biochar production also offers potential in the agriculture, energy and waste management sectors.