Biomass sustainability - key issues explained

Kenneth Richter

03 May 2013

Industry has criticised us for raising concerns about the burning of trees in power stations. But is it right?

The Renewable Energy Association (REA) has accused Friends of the Earth, Greenpeace and RSPB in the Guardian of "spreading misinformation" when we have called for limits to "green energy" subsidies being paid to support the burning of wood in power stations.

So what's the story here?

Friends of the Earth believes that bio-energy has a role to play in bringing down greenhouse gas emissions. But only if it is done in a way that protects wildlife, people's livelihoods and guarantees emissions cuts.

When wood is burnt in a power station CO₂ is released into the atmosphere, just as it is with fossil fuels. But currently this CO₂ is not counted in the Government's proposed greenhouse gas standard even though it is the single largest emission associated with bioenergy. This is justified by the assertion that the CO₂ is immediately neutralised by regrowth in the forest from which the wood was harvested.

In effect, what actually happens is that the wood is harvested and burnt, emitting CO₂ into the atmosphere and creating a 'carbon debt'. This debt may be repaid by recapture of carbon - sequestration - from regrowth and from growth in the wider forest, but depending on the sequestration rate it may take many decades for the end of pipe emissions to be neutralised.

There is a growing body of academic evidence that confirms this.  In a review of the evidence in 2011, the European Environment Agency concluded that:

"Producing energy from biomass is meant to reduce GHG emissions. But burning biomass increases the amount of carbon in the air if harvesting the biomass decreases the amount of carbon stored in plants and soils, or reduces ongoing carbon sequestration [...] legislation that encourages substitution of fossil fuels by bioenergy, irrespective of the biomass source, may even result in increased carbon emissions"

In addition, DECC has recently released a prototype greenhouse gas calculator for biomass electricity. It estimates the net emissions as a result of the CO₂ that is released on combustion and the sequestration in the forest over a 20 year time period. The calculator also estimates the impact on emissions if wood is used by the energy industry instead of others, such as in construction.

The emissions for scenarios that involve the intensification of forest management, i.e. increasing harvest rates, or diverting wood away from other industries mostly result in emissions that are significantly higher than fossil fuels. Only the scenarios based on using residues that would otherwise be unused and energy crops such as willow offer significant emission reductions.

It is vital to distinguish between different forms of bioenergy based on their real carbon impacts. We are asking DECC to include their carbon calculator in the forthcoming sustainability criteria for biomass.

The REA might not like what science says about the climate impacts of burning of trees for energy, but it is difficult to see how they can continue to ignore it. We are engaged in an ongoing dialogue with the REA about this issue.