How green is bioenergy?

Bioenergy-123rf

 It is well known that there is an international effort to replace fossil energy with biomass in an effort to reduce greenhouse gas (GHG) emissions and curb global warming. It was widely assumed that biomass combustion would be inherently 'carbon neutral' because it only releases carbon taken from the atmosphere during plant growth. However, there have been arguments with regard to the neutrality of bioenergy and the assumption that replacing fossil-sourced energy with bioenergy will in fact reduce GHG emissions. It turns out it is more complicated than once thought. For this reason the European Environment Agency (EEA) scientific committee has reviewed this assumption and has called for “a major revision of EU policies and directives related to bioenergy.”

The review, based on analysis by the Potsdam Institute for Climate Impact Research, concluded that the assumption that biomass combustion would be inherently 'carbon neutral' is incorrect. Of course, plants grown for bioenergy do absorb carbon dioxide (CO2), but this carbon neutrality way of thinking results in a form of double-counting, as it ignores the fact that using land to produce plants for energy typically means that this land is not producing plants for other purposes, which would continue to absorb carbon and help to reduce CO2 from the air, i.e. carrying out carbon sequestration. Present EU rules do not properly account for indirect land use change in the context of bioenergy policies and do not therefore consider the full GHG effects of bioenergy.

The EEA paper says that “because bioenergy does not physically reduce emissions from exhaust pipes and chimneys, it must be true mathematically that bioenergy can reduce greenhouse gas emissions (except by reducing other human consumption of biomass, such as food) only if, and to the extent that:

  1. land and plants are managed to take up additional CO2 beyond what they would absorb without conversion into bioenergy, or
  2. bioenergy production uses feedstocks, such as crop residues or wastes, that would otherwise decompose and release CO2 to the atmosphere anyway.”

Only biomass grown that is in excess of that which would be grown anyway or biomass that would otherwise decompose is “additional biomass," which contains "additional carbon,” and has the potential to reduce greenhouse gas emissions, when used for energy.

Based on analysis by the Potsdam Institute for Climate Impact Research, the Scientific Committee recommends that:

   1. European Union regulations and policy targets should be revised to encourage bioenergy use only from additional biomass that reduces greenhouse gas emissions, without displacing other ecosystems services such as the provision of food and the production of fibre.

   2. Accounting standards for GHGs should fully reflect all changes in the amount of carbon stored by ecosystems and in the uptake and loss of carbon from them that result from the production and use of bioenergy.

   3. Bioenergy policies should encourage energy production from biomass by-products, wastes and residues (except if those are needed to sustain soil fertility). Bioenergy policies should also promote the integrated production of biomass that adds to, rather than displaces, food production.

   4. Decision makers and stakeholders worldwide should adjust global expectations of bioenergy use to levels based on the planet's capacity to generate additional biomass, without jeopardizing natural ecosystems.

A few scientists, me included, have maintained that bioenergy from wastes, be it crop residue or anaerobically digested waste, is the way forward, since these wastes, e.g. crop residues and other organic waste, would otherwise be disposed of and allowed to decompose. Burning crop residues instead of fossil fuels still emits carbon, but it is offset because it has the effect of reducing the carbon emitted during decomposition of this waste material.

You can stay informed about the latest developments on biofuels by joining the CABI Biofuels Information Exchange (http://biofuelexperts.ning.com/) for free access to over 35,000 research records on biofuels from our CAB Abstracts Database, as well as links to pertinent third party biofuels reports and books, news summaries, discussion forum and more!

Link to the EEA paper.

Image courtesy of http://www.123rf.com

Further Reading

   1. Gelfand, I.; Zenone, T.; Jasrotia, P.; Chen, J.; Hamilton, S. K.; Robertson, G. P. (2011) Carbon debt of Conservation Reserve Program (CRP) grasslands converted to bioenergy production. National Academy of Sciences, Washington, USA, Proceedings of the National Academy of Sciences of the United States of America, 108, 33, pp 13864-13869, 47 ref.

   2. Valente, C.; Hillring, B. G.; Solberg, B. (2011) Bioenergy from mountain forest: a life cycle assessment of the Norwegian woody biomass supply chain. Scandinavian Journal of Forest Research, 2011, 26, 5, pp 429-436, 40 ref.

Lisboa, C. C.; Butterbach-Bahl, K.; Mauder, M.; Kiese, R. (2011) Bioethanol production from sugarcane and emissions of greenhouse gases – known and unknowns. GCB Bioenergy, 3, 4, pp 277-292, many ref.

   3. Johnson, D. R.; Willis, H. H.; Curtright, A. E.; Samaras, C.; Skone, T. (2011) Incorporating uncertainty analysis into life cycle estimates of greenhouse gas emissions from biomass production. Biomass and Bioenergy, 35, 7, pp 2619-2626, 34 ref.

   4. Cascone, G.; D'Emilio, A.; Buccellato, E.; Beccali, M.; Trupia, S. (2008) Biogas and electrical power cogeneration through anaerobic digestion of vegetable residual from tomato greenhouse cultivation. European Society of Agricultural Engineers, Silsoe, UK, Agricultural and biosystems engineering for a sustainable world – International Conference on Agricultural Engineering, Hersonissos, Crete, Greece, 23-25 June, 2008, pp P-027, 8 ref.

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