This biogenic carbon should not be confused with fossil carbon which comes from things like coal, oil and gas.
When burning wood for heating, it’s the carbon that’s burning. This produces CO2 which is released back to the environment. This CO2 is still referred to as biogenic because it came from a biological source. It forms part of what’s known as the biogenic carbon cycle.
The CO2 released by burning wood for heating gives the same environmental result as if the tree had died or been felled for timber. If wood is left to decay, the carbon is returned to the environment, just a little later than if burned. Many organisms benefit from the carbon in decaying wood, but these organisms will also give up this carbon when they die. If we build or make things with wood, then once it has finished being useful, one way or the another, the carbon in the wood is returned to the environment.
So, the more trees we have, the better, for lots of reasons. Not least of all because wood is a sustainable, low carbon fuel. Processing and transporting our wood for fuel produces a little CO2 of course, but even this will reduce to zero as the whole of industry progressively decarbonises.
Tens of millions of trees are scheduled to be planted in new woodlands over the coming years, adding to all of the new areas planted since year 2000. To maximise biodiversity and carbon capture, woodlands require management. A significant management tool is thinning and felling. It is very beneficial for biodiversity to leave some woody material as food and habitat for all sorts of organisms. But there is a valuable surplus that can be harvested for wood fuel as a cash crop.
Biogenic carbon CO2 cycle
- Carbon dioxide (CO2) from air is absorbed by trees, plants and living things as ‘biogenic carbon’
- Trees store the CO2 (biogenic carbon) in the wood’
- Processing wood for fuel currently produces very small amounts of CO2 per kilowatt of heat (even this will fall to zero as all industry decarbonises).
- Decomposing wood returns CO2 back to the air. Burning biogenic carbon for heating returns CO2 back to the air and soil and the cycle begins again.
So whether wood decays naturally or is used for building or making things, or if it’s burned, the carbon (CO2 ) is always biogenic and will be returned to the natural environment to start the process again.
Is wood fuel sustainable?
The definition of sustainability is ‘the use of natural resources when this use is kept at a level that is not likely to damage the environment’. So it depends if the trees are replaced. There are extensive government commitments to new planting. In addition, there is extensive new private planting. Existing woodland that is felled is almost always replanted. So yes, wood fuel is very sustainable, after all, it actually does grow on trees. Tree growing in the UK
Comparing CO2 from wood with other fuels see the links for details of supporting documents and reference material.
Electric heaters v’s efficient wood stove – Generating 1kW of heat from a modern stove produces 1/19th of the CO2 emissions of direct electric heating (at current grid carbon intensity and current wood processing and transport carbon intensity).
So how does that work? Broadly, a little over 40% of current grid electricity is generated from renewable sources. So currently, just under 60% of the electricity used to generate 1kW of heat from a plugged in electrical heater comes from burning fossil fuel, which obviously produces CO2. The CO2 emissions produced from generating 1kW of heat from wood burning come only from the processing and transport of the wood and not from burning it. The CO2 released when burning wood for heating is part of the biogenic cycle and forms part of the natural (non-fossil) carbon cycle.
Heat pumps are very efficient. But at current grid carbon intensity levels, even a good heat pump produces around 5 times as much CO2 per kW of heat as an efficient wood stove. Of course, the CO2 emitted through using a heat pump will reduce over time as more of our future electricity is generated from renewables. But, by the same token, the CO2 emitted through the processing and transport of wood will reduce to zero over time as all of our industry decarbonises.
Mains gas v’s efficient wood stove: The government information in this link shows that wood fuel produces 1/16th of the CO2 emissions as mains gas.
See some wood fuel carbon facts with links and references.
Further references to the use of wood as fuel can be found at Stove Industry Association
