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Biomass Energy Has Big Climate Impact Even Under Best Case Scenario

Study Dispels Assumption that Burning Forest Residues for Energy is Carbon Neutral


Cutting down trees to generate electricity is completely bonkers. See below for a news release about a new peer-reviewed paper by the Partnership for Policy Integrity’s Director, Mary Booth, showing that even when forestry wastes are burned as biomass energy, the carbon dioxide emissions will significantly undermine efforts to reduce greenhouse emissions.  Dominion Energy laughably claims on its website that “in our electric utility service territory in Virginia, this fuel [biomass] is primarily derived from waste wood, the smaller tree tops and branches left behind in the forests as part of the logging process for roundwood.” Even if this statement is true (Dominion has said elsewhere that its biomass includes “small trees”), Dr. Booth’s paper shows that the company’s use of wood waste is likely to have a negative impact on greenhouse emissions. I encourage everyone to submit comments (to Karen.Sabasteanski@deq.virginia.gov) about Virginia’s cap-and-trade plan to the Department of Environmental Quality by April 9 and to request that the Commonwealth count carbon dioxide emissions from biomass energy under the plan. 

Biomass Energy Has Big Climate Impact Even Under Best Case Scenario

New Study Dispels Assumption that Burning Forest Residues for Energy is Carbon Neutral

February 21, 2018

Pelham, MA.  Burning wood in power plants will significantly undermine efforts to reduce greenhouse emissions over the next 10 – 50 years even under industry best-case scenarios where only forestry wastes are burned as fuel, according to a study published in Environmental Research Letters.

“Not Carbon Neutral: Assessing the net emissions impact of residues burned for bioenergy,” by Mary S. Booth, Ph.D., assesses net CO2 emissions from burning tree tops and branches left over from forestry operations. Such materials are often considered to have zero net greenhouse gas emissions since they are assumed to emit CO2 from decomposition or incineration even if they are not burned for energy. The paper explodes this fallacy by demonstrating that even when power plants burn true wood residues and exclude whole trees specifically cut for fuel, net emissions are still significant.

“To avoid dangerous climate warming requires us to reduce power sector CO2 emissions immediately,” said Mary Booth, author of the study. “However, this analysis shows that power plants burning residues-derived chips and wood pellets are a net source of carbon pollution in the coming decades just when it is most urgent to reduce emissions.”

The study examines the net CO2 emissions impacts of biomass burned in US power plants and exported wood pellets that are burned to replace coal at the UK’s massive Drax power station and other power plants in the EU. Combined, these facilities consume tens of millions of tonnes of wood per year. The study acknowledges that wood pellets are often sourced from whole trees, not forestry residues, but evaluates carbon emissions from residues-derived pellets because the biomass industry so often claims residues are a main pellet feedstock. It finds that even assuming the materials burned are true residues, up to 95% of the cumulative CO2 emitted represents a net addition to the atmosphere over decades.

“Drax and other wood-burning power plants emit as much or more CO2 per megawatt-hour as when they burn coal, but the policy of treating biomass as having zero emissions means companies avoid paying fees for biomass carbon pollution,” said Mary Booth. “This analysis shows that holding companies accountable for biomass CO2 would reflect the atmospheric carbon pollution impact better than treating biomass as carbon neutral.”

The paper includes a method for weighting CO2 emissions from biomass power plants so they can be counted under carbon trading and renewable energy subsidy programs.

The UK paid £809 m (about $1.2 b) in renewable energy subsidies to bioenergy in 2015, in addition to subsidies for zero-emissions wind and solar energy, and bioenergy is anticipated to grow significantly in the coming years. The analysis shows that increasing bioenergy to levels projected by international climate modeling would emit around 9 billion tonnes of CO2 per year at the smokestack, and that cumulative atmospheric CO2 loading would be a high percentage of those stack emissions.

Like other recent papers on bioenergy, Booth’s study finds that burning wood for energy is not compatible with Paris Agreement goals to reduce carbon pollution in the coming decades, but additionally demonstrates that net CO2 emissions are large even under the biomass industry’s best case scenario where biomass is sourced from residues, rather than whole trees.

The paper is accompanied by a short video abstract illustrating its main findings, and is available for download at http://iopscience.iop.org/article/10.1088/1748-9326/aaac88.

  • Kenneth Ferland

    Having read the study in full I believe you have cherry picked from it and that the study itself is lacking in several regards.

    First off the core calculation they are performing is to compare 2 trees, one that is knocked down and starts to decompose on the forest floor releasing CO2 slowly, and another that is immediately processed to pellets and used as fuel. Some fossil fuel is used in processing, mainly transport and drying of the wood and this is added to the ‘fast’ scenario. They then look at the ratio between these numbers at various points in time to see what portion of fast-burn scenario’s emissions that would not have occurred ANYWAYS under the decomposition scenario. For example burning a tree produces 1000kg of CO2, 100kg of which is from fossil fuels used in processing and 900kg from the wood itself, but if left to rot over 10 year the tree would have released 400kg, thus 60% of the burning scenario emissions are ‘surplus’, and we want to get the lowest level of surplus emissions possible. The longer the time we allow the tree to rot the more CO2 it would release, but only up to 900kg, so even over an infinite time the surplus will never reach zero.

    This is the first major flaw, they are not considering the fact that tree’s grow back, the whole calculation is essentially treating wood as a non-renewable resource. Forestry practices in Virginia is not reducing our forested land, urban sprawl and conversion to agriculture is causing a slight decline in area, but total mass of standing wood is rising about half a percent a year. Neglecting this is a huge hole in the study.

    Now for cherry picking, the 95% figure is for the shortest time frame (10 years) which I find unreasonable given how long term climate change is as a problem and how long trees take to grow and decompose. Second the use of the ‘k’ factor for the decomposition rate, they use a high value, a low value and a middle value, only the middle value is experimentally derived and it’s from a study of North Carolina which is an excellent analog for Virginia. When you look at a 40 year time frame with appropriate decomposition rates the numbers come down into the 33% range, far from the shock value headline numbers.

    Note the the paper is also arguing for UK policy changes, basically that they reduce the amount of carbon credits given to wood fired power plants. So rather then their wood fired emissions being entirely un-carbon taxed they would instead get taxed on that 33% number. After all if were consuming fossil fuel in the US to made what they are burning those emissions should get counted the same for a person who made wood pellets in the EU and had to pay taxes on any fuels they used.

    So the question of how much credit wood pellets get and how much of a market their is for them is really out of our hands. All we can do is try to set policy in the US which will encourage the best practices so that EU carbon-taxes applied to wood imports will be as low as possible. We already know what those practices are and many of them will actually raise wood production and employment.

    First and most importantly re-plant aggressively, most private land owners simply allow their land to be logged as a cash cow and put zero inputs into it, letting it grow back a generation later to be re-logged. Better practices can reduce that cycle time hugely raising the earnings of land owners and employing more foresters. Subsidize and ideally mandate replanting. Second look into lowering the fossil fuel inputs to pellet making much of which is in drying, methods to let wood dry passively will pay huge dividends here. To reduce transport costs look at larger numbers of smaller plants close to wood sources, followed by reducing truck emissions. Studies have already shown that best practices CAN produce wood pellets which are extremely close carbon-neutral and if put in place they will ensure the growth of this local industry even after changes to EU regulations, and if Virgina can get ahead of the curve we stand
    to gain market share if our pellets are categorized as greener.