burning, largely resulting from the activities of man, accounts
for between 20 and 40 million tonnes of methane emissions each
year. Methane emissions arising from biomass burning are a result
of incomplete combustion and huge amounts can be produced during
large scale burning of woodlands, savanna and agricultural waste.
In savanna regions of the world, burning is often carried out
every few years to promote regeneration of the vegetation. The
importance of methane emission from biomass burning can be overshadowed
by the large amounts of carbon dioxide which are also produced,
but in many cases the subsequent regrowth, and carbon dioxide
uptake, of previously burned woodland and savanna areas means
that the net emission of carbon dioxide is much reduced.
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 methane emissions from
such natural biomass burning. Huge areas of woodland and grassland
are now periodically burned for land clearance.
Burning of agricultural waste also produces significant amounts
of methane due to its generally high water content. Additionally,
wood burning as a domestic fuel source and for charcoal production
release significant amounts of methane 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
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, and
avoiding incomplete combustion, 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.