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Biomass as an energy source

David Hall argues that biomass provides an effective energy substitute for fossil fuels as well as a sink for sequestering carbon.

Professor David O Hall is a faculty member of the Department of Life Sciences, King's College London, United Kingdom.

At first reading, the Kyoto Protocol, in strengthening the climate treaty targets, appears only to advocate planting and conserving of trees — “afforestation and reforestation” — in order to create carbon sinks in the trees themselves and also in soils. Little is said about using the trees, and other, biomass as an energy source to substitute the use of carbon dioxide-emitting fossil fuels.

It has, however, been recognized for at least a decade that growing and using biomass on a continuous basis as a substitute for fossil fuels has clear advantages compared to using the biomass solely as a means to sequester carbon to create a carbon sink.

Renewably-grown biomass is a carbon dioxide-neutral fuel with a low sulphur content and can be converted to electricity, heat, and liquid and gaseous fuels. The biomass is grown perennially to generate energy so that environmental benefits such as soil conservation and biodiversity protection accrue in comparison to annual crops.

In addition, rural communities gain jobs rather than removing land from productive use only to sequester carbon.

Thus, there are numerous environmental and social advantages to be gained from growing and producing biomass energy.

The problems with growing biomass solely as a carbon sink are that:

  • once the trees or plants reach maturity they start losing their stored carbon; and,
  • maintenance and protection costs are incurred throughout the lifetime of the trees.

However, when growing biomass with defined (short) rotations and using it as a source of fuel, income is generated continuously thereby creating local jobs and other benefits.

Indeed, trying to maintain carbon sink forests for long periods of time may be very difficult unless rigid legal and fire protection systems are enforced. People may need to be excluded in order to prevent damage to carbon sinks. This may not be feasible in many countries unless an effective long-term infrastructure exists.

Naturally, where mature forests exist they should be conserved as both carbon sinks and deposits of biodiversity. Also, where biomass energy plantations are grown — probably on excess arable and degraded land — they must follow ecological guidelines so as to improve above- and below-ground biodiversity and carbon sinks.

Balancing the short- and long-term carbon and income benefits of these two approaches — substitution vs. sequestration — on a given piece of land depends on numerous factors such as yield and rotation, which can be modelled.

What is the potential role of biomass energy in the implementation of Articles 6 and 12 of the Kyoto Protocol which deal with carbon credits and cooperative projects, such as Activities Implemented Jointly, between countries?

It is considerable if the various predictions made by the Intergovernmental Panel on Climate Change, the multinational Shell, the International Energy Authority, the United Nations Conference on Environment and Development and other bodies are to be believed.

All these forecasts indicate that after the year 2020 biomass and some other renewable energies will be major players in all new energy supply systems. There is also every reason to believe that well before then biomass could substantially substitute for fossil fuels, as is already happening in a number of countries.

Clearly, biomass for energy to offset fossil fuel use and interim sequestering of carbon in the growing biomass and soils should be a component of Joint Implementation and the Clean Development Mechanism — provided that verifiable and transparent monitoring is undertaken from baseline to completion while ensuring local people benefit from the start to end of such land-use projects.

An example of the immediate relevance of biomass energy is presented in the recent European Union White Paper on Renewable Energy which proposes that Europe could double its renewable contribution from 6 per cent today to 12 per cent by the year 2010. This would substantially help meet the Kyoto Protocol targets.

Biomass energy in total could contribute an additional 90 million tonnes oil equivalent per year compared to today’s annual contribution of about 47 million tonnes. Of this additional energy, “energy crops” (trees, woody grasses, and so on) are proposed to provide 45 million tonnes oil equivalent per year which could be grown on about 13 million hectares of land (based on 4 per cent of total land at a yield of 10 tonnes per hectare and conversion efficiency of 75 per cent).

This extra 45 million tonnes oil equivalent per year of renewable, carbon dioxide-neutral biomass energy would reduce carbon dioxide emissions by 50 million tonnes of carbon per year compared to the present European Union annual carbon total of 890 million tonnes.

The contribution of all forms of biomass (137 million tonnes oil equivalent) to reducing carbon dioxide emissions would total about 150 million tonnes of carbon by the year 2010, that is, a reduction of 17 per cent, twice the European Union’s obligation under the Kyoto Protocol.

A clear point for policy makers is that trees and other forms of biomass can act as carbon sinks, but at maturity or at their optimum growth rate there must be plans to use the biomass as a source of fuel to offset fossil energies (or as very long-lived timber products). Otherwise, the many years of paying to sequester and protect the carbon in trees will simply be lost as they decay and/or burn uncontrollably.

Biomass has many advantages for an environmentally-friendly future. To obtain maximum benefit, trees, other than in primary forests, should be used as an energy source or long-lived product at the end of their growing life. It is probably preferable in most circumstances — except in mature and primary forests — to use the biomass on a continuous basis as a substitute for present and future fossil fuel use.

Further information

David O Hall, Department of Life Sciences, King's College London, London W8 7AH, UK. Fax: 44-171-3334500. Email: Web:

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