Exact CO2 emissions from biomass burning are difficult to quantify due to a dearth of information on fire-carbon fluxes, and the longer-term balance of carbon emissions with carbon uptake by regrowth of vegetation. In savannah regions of the world, burning is often carried out every few years to promote regeneration of the vegetation. Large amounts of CO2 are therefore produced, but in many cases the subsequent regrowth and CO2 uptake of savannah areas mean that the net carbon emission is much reduced or completely negated. Biomass burning is therefore an important short-term source of CO2. In the longer term it can actually contribute to a net carbon sink in the form of relatively stable 'black carbon' deposited to the soils where burning has taken place (as discussed in Section 1.5.3).
Huge areas of woodland and grassland are periodically burned for land clearance, with this change in land use often reducing the size of the soil and vegetation carbon sinks, thus having the net effect of increasing concentrations of CO2 in the atmosphere. Additionally, wood burning as a domestic fuel source and for charcoal production releases significant amounts of CO2 on a global scale. Accidental fire and arson account for further large-scale biomass burning events each year. The uncontrolled way in which most biomass burning occurs means that the only real route to reducing emissions from this source is to lessen the amount of burning itself. Some biomass burning is required if environments such as the savannah are to be retained, but it is the large-scale destruction of forest areas for cash crop agriculture and urban spread that stands out as an area to be tackled.
Controlled biomass burning is being developed as an alternative to traditional fossil fuel-based energy production, with power stations fuelled by forest residues already a reality. By making use of a renewable resource like pinewood chips, these biomass power stations are able to have a greatly reduced net greenhouse gas impact per kilowatt-hour of energy output. The CO2 they release is effectively in a closed loop, where it is incorporated into more trees, which, when large enough, are harvested and used to fuel more energy output from the biofuel power plant.
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