|
Biomass fuels include woody materials that can be burned, fuel crops, industrial residues, agricultural wastes and methane generated by domestic and industrial wastes.
Some of these fuels have relatively low energy contents and produce both substantial amounts of pollution and high CO2 emissions when burnt. But they all have one important advantage over fossil fuels: they are part of the fast carbon cycle.
If a tree falls in the forest and is left to rot, it will decay within several decades and most of its carbon will return to the atmosphere (either as CO2 or CH4, or both).
If we burn the wood instead, we can use the energy. In this case the carbon will return to the atmosphere immediately as CO2. Either way, the carbon will be recycled relatively quickly back to the atmosphere.
When we burn fossil fuels, on the other hand, we are quickly releasing
the slow-cycle carbon back to the atmosphere, and we are upsetting
the balance of the carbon cycle. For the earth’s atmosphere
to be in equilibrium with life, and with the output of energy from
the sun, it is important that fossil-fuel carbon stays locked up in geological
materials.