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 Exact
carbon dioxide emissions from biomass burning are difficult to quantify
due to a general dearth of information on fire-carbon fluxes and
the longer term balance of carbon emissions and uptake by regrowth
of vegetation.
Indeed, in savanna regions of the world, burning is
often carried out every few years to promote regeneration of the
vegetation. Large amounts of carbon dioxide are produced, but in
many cases the subsequent regrowth and carbon dioxide uptake of
savanna areas means that the net emission of carbon dioxide is much
reduced or completely negated.
Biomass burning is, then, an important short term
source of carbon dioxide. In the longer term it can actually contribute
to a net carbon sink in the form of relatively stable 'black carbon'
in the soils where burning has taken place.
Human Impact
Though fires caused by lightning strikes have, and still do, account
for some large biomass burning events, the activities of man in
the last 100 years have dwarfed carbon dioxide emissions from such
natural biomass burning.
Huge areas of woodland and grassland are periodically burned for
land clearance, with this change in land use often reducing the
size of the carbon sink and having the net effect of increasing
concentrations of carbon dioxide in the atmosphere. See Carbon
dioxide Sources - Land use.
Additionally, wood burning as a domestic fuel source and for charcoal
production release significant amounts of carbon dioxide on a global
scale. Accidental fire and arson account for further large scale
biomass burning events each year around the world.
Potential for control
The uncontrolled way in which most biomass burning happens means
that the only real route to reducing emissions from this source
is to reduce the amount of burning itself. Some biomass burning
is required if environments such as the savanna are to be retained,
but it is the large scale destruction of forest areas for cash crop
agriculture and urban spread which stand out as areas to be tackled.
Controlled biomass burning is currently being developed as an alternative
to traditional fossil fuel energy production methods, with power
stations fuelled by wood chips and the like already a reality. By
making use of a renewable resource, like pine wood chips these biomass
power stations are able to have a much reduced net greenhouse gas
impact compared to equivalent coal, oil and gas fired power stations.
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