Wood: a burning question

Wood Pellets

Wood Pellets (Photo credit: Alternative Heat)

Yesterday a little-noticed but important policy reversal took place. The UK government announced that subsidies for dedicated biomass-burning power plants are to be capped, and subsidies for biomass burning in existing power stations will end by 2027.  There are many competing truths flying around the question of burning wood for power generation, and the misguided subsidy policy was inspired by one of the worst of them.

Wood has for some time been touted as a big part of the solution to our carbon problem.  European governments see it as one of the easiest ways to meet their emission reduction commitments.  Drax, the largest coal-fired power station in the UK, has announced its intention to transform itself into a predominantly biomass-fuelled generator.  Wood is carbon neutral, we are told, so we can burn as much as we like with a clear conscience.

Lets challenge that truth head on.

It is true that if you grow a tree (or any other plant matter) from seed, without expending any energy on its cultivation (by irrigation etc) and then burn it in the same location then no net carbon is released into the atmosphere.

That never happens.

Leaving aside the fuel burnt in tractors, chainsaws and foresters’ cars, and the electricity used to irrigate saplings, a great deal of energy is typically expended in hauling biomass around the world.  Drax CEO Dorothy Thompson recently had to admit on the BBC’s Bottom Line that most of the biomass to be burnt in their furnaces would come from North America.  Furthermore, Drax — just like domestic biomass boilers — needs its wood converted into pellets, a process that requires considerable energy inputs.

Proponents of biomass pellets assure us that notwithstanding the “embodied carbon” resulting from pellet manufacturing and transport, biomass pellets still have a far lower carbon footprint than coal.  That’s a truth that depends entirely on the type of biomass being used to make the pellets.

One of the most important truths ignored by fans of biomass burning is this: burning a tree can release just as much carbon into the atmosphere as burning the energy equivalent in coal.  The only way to make the action carbon neutral is to plant another tree in its place and wait the many years it takes to grow to the same size.  In other words, if you burn an established tree you run up a carbon debt which cannot be paid off for decades.  It is true that this process might be carbon neutral over the very long term but, as campaigners keep telling us, our greenhouse gas challenge is rather more urgent than that.  If you are concerned about melting icecaps and rising temperatures over the next few years, you’d better make sure your wood pellet provider is not using established trees as their biomass source.

Some claim that we can get all the biomass we need from the offcuts from the timber industry and the waste residues from sustainable forestry.  Really?  Drax alone will burn seven million tonnes of biomass each year; the UK’s total wood production is ten million tonnes.  Although Drax likes to give the impression it will only be burning “energy crops”, offcuts and forestry residues, a recent Freedom of Information request by Biofuelwatch has uncovered evidence from the Department of Energy and Climate Change that Drax’s boilers will require wood from whole trees; “waste” biomass is unsuitable for their equipment.

The other truth that is routinely ignored by biomass burners is the opportunity cost of the land on which the biomass is grown.  Say you have a hypothetical empty piece of fertile land: you could grow biomass to cut down and burn, or you could grow food, cotton and other essential plant products (including wood for construction and furniture).  If you choose to grow biomass for burning, then the food, cotton, building materials et al to feed, clothe and house a rapidly expanding and increasingly demanding global population will have to be grown on other land.  Often that land has to be first cleared of primary forest — probably by burning it and releasing all of its stored carbon into the atmosphere.  An even more tragic case of this perverse outcome is the large-scale clearing of rainforest that has taken place in countries like Indonesia and Malaysia to make way for palm oil plantations to feed our demand for another type of “carbon neutral” biofuel.  Leaving aside the desperate loss of ecosystems and biodiversity, this kind of outcome is hardly helpful to our net global carbon emissions.

“Carbon neutral” has become one of the most highly prized labels of our age.  There is always going to be some way to present it as a truth.  But next time someone proposes a grand solution to all our climate and energy problems that involves burning a load of trees, please challenge them with a few competing truths.


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