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By Nathanael Greene on Jun 13, 2010 with 6 responses

New Study: Burning Trees for Power Worse for Climate than Burning Coal

Tags: biomass, EPA

A study commissioned by MA Department of Energy Resources and released last week reaches the conclusion that burning trees to make electricity is worse for the climate than burning coal at least through 2050. In fact, the study by the Manomet Center for Conservation Science finds that between the release of carbon when trees are burned and the slow reabsorption as the trees regrow, that this source of biopower would increase emissions by 3% compared to coal power over 40 years.

This will come as a shocker to some, but it really shouldn’t. Wood contains less energy per pound of carbon and forests, especially in the northeast grow slowly. So when we burn a tree, we’re releasing more carbon and getting less energy than we would if we burned coal and then re-absorbing that carbon very slowly.

In other words, not only is biopower from trees not carbon neutral, it’s worse for global warming than the worst fossil fuel. This myth of carbon neutrality has been a big part of the biomass industry’s lobbying. It came up from surprising and unfortunate corners in yesterday’s Senate vote to protect EPA’s ability protect our air quality. Hopefully this report will put an end to the silly idea.

But in busting the myth, we have to be careful that we not ignore some of the reports conclusions or overstate them. For instance, this AP story ignores the conclusion that using trees for combined heat and power can provide a 25% reduction in GHG emission compared to oil. Furthermore the report doesn’t look at carefully sourced wastes and residues or biomass grown on fallow or degraded lands.

The right lesson for policy makers to take from this study is that we have to carefully account for the carbon associated with bioenergy. I’ve written about the importance of getting this accounting right before and just recently 90 scientists called on Congress to get it right in climate legislation and energy policy. Efficient uses of the right sources of biomass can provide an important supply of low carbon energy, but you don’t get that if you pretend that it’s all the same let alone all carbon neutral.

  1. By rrapier on June 13, 2010 at 4:39 pm

    I think that can be true, but it doesn’t have to be true. It all depends on how you grow the trees (clear-cutting old growth forest to burn has a much different impact than sustainably farming trees), the process you use to convert the trees, and the pollution mitigation of your power plant.


  2. By paul-n on June 14, 2010 at 2:14 am

    Wood contains less energy per pound of carbon

    Nate, have you got a source for that?

    Here’s how I see the numbers. (data from ORNL  here)

    Bituminous coal has an energy value of 27Mj/kg, and is 75% carbon, so you get 36MJ per kg of carbon

    Wood (dry basis) is typically 18-22MJ/kg, and is 50% carbon, so you get 36 – 44MJ per kg of carbon.

    So at worst it’s even, and at best, wood has a lower carbon intensity.


    Also, the carbon is “neutral” as it is sourced from biomass.  The real problem is that certain land management practices can release soil carbon, but this is true of some farming farming prectices, and even municipal waste disposal, in addtion to forestry.

    Land that is cleared for property development results in just as much CO2 emissions as the same land being cleared for Biomass.

    But what if we just take out a few trees per acre per year, roughly equal to the forest growth rate? (a neighbour of mine does this) This would most certainly be carbon neutral in the forest, and thus so is the total energy.

    A biomass tree farm (there is one down the road from me) with a seedling to harvest cycle of ten years, is in carbon dividend from day one, assuming a start from bare land (this one is on mine waste piles!)

    I think this report is bit misleading.

    The real issue here is that clear cutting forests leads to increased CO2 emissions, period, and should be carbon taxed accordingly, regardless of whether the wood is burned or milled.  


    We should not blame the wood if improper practises are used to get it. 

    The Forest Stewardship Council has a good system for lumber, this could equally be applied to wood for energy.  if you qualify for FSC certification, then you are doping it right and will be carbon neutral.  If you don;t then you shouldn’t really be allowed to operate, until you do.

    There are “clean” and “dirty” ways to get oil (oils sands, coal to oil, etc).  The end product has the same CO2 emissions, it’s the process to get there that matters, the same applies to wood.

  3. By Marcel F. Williams on June 14, 2010 at 1:09 pm

    You could always capture and pipe the CO2 to a synfuel production facility that uses hydrogen produced from off-peak electricity from a nuclear, hydroelectric, solar, or wind facility. With CO2 and hydrogen, you can make carbon neutral: methane, methanol, gasoline, diesel fuel, and jet fuel. Oxygen created in the production of hydrogen could be piped to the wood power plant to improve the efficiency of producing electricity.

  4. By paul-n on June 18, 2010 at 12:58 am

    marcel, to capture the CO2, from combustion, you face the same issues as for coal, separating it from the air, compressing etc.  

    In theory, you could use oxygen blown gasification to get a pure CO2 stream, and then use thew wind to make the methanol, but you are better off doing that with the wood directly.  You also have the problem of the methanol production being a continuous, medium temperature process, which is not conducive to intermittent wind energy.  You can store the O and H, of course, but that is signifiacnt extra cost too.

    probably a better use for wind is to liquefy air, for industrial n2 and O2 production, as this is a physical, not chemical process, and can be stopped and started according to the wind, and easily and cheaply stored.

  5. By Dynamo Dan on July 5, 2010 at 11:05 am

    This is really stupid. No matter how you slice it and dice it, the carbon in coal comes from underground, and the carbon in a tree comes from the atmosphere. Trees take carbon from the atmosphere that was already there, coal adds carbon to the atmosphere that wasn’t there to begin with. What a spectacular example of politically motivated “science.”

  6. By Wendell Mercantile on July 5, 2010 at 9:42 pm

    No matter how you slice it and dice it, the carbon in coal comes from underground, and the carbon in a tree comes from the atmosphere.




    Exactly where do you think the peat moss, giant ferns, tree leaves, and other organic matter that were transformed into coal over millions of years got their carbon? The carbon in coal has been underground for a long time, but that’s not where it came from. It came from the atmosphere, just like the carbon in the tree I cut down this spring.  And for that matter, just like the carbon in petroleum which was originally locked up in algae and phyto-plankton, but also originally came from the atmosphere.


    Like it or not, the earth’s atmosphere once contained far more CO2 than it does today.



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