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close this bookBoiling Point No. 33 - May 1994 Number 33 (ITDG - ITDG, 1994, 36 p.)
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View the documentNews
View the documentR&D News
View the documentPublications
View the documentLetters


Dear Editor,

Boiling Point number 31 contained, as an insert, a summary of a paper by Kirk Smith entitled The case for stove programmes. One of the points of the paper is to alert the reader to the potential global warming effects from the incomplete combustion of biomass, particularly wood, in domestic stoves. However, the analysis in the article is misleading as it only looks at one side of the pollution equation.

From a small experiment in Manila a table was produced of the emissions of gases and particulates from LPG, kerosene, charcoal, and wood. It is implicitly assumed that carbon monoxide, methane, non-methane organic compounds and respirable suspended particles are additional substances formed when the biomass is burned in domestic stoves and that the gases contribute to global warming.

In order to give a balanced picture, the article should have examined what would have happened to the wood and other forms of biomass if they had not been burned in domestic stoves.

In developing countries, the annual increment of wood from all tree resources is about three times annual wood consumption. Granted, in most of these countries there are areas where wood is scarce and it is cut down faster than it grows, but the main cause of deforestation is as a result of agricultural expansion.

If the wood and other forms of biomass are not burned in stoves they will decompose naturally into various gases and solids, be burned in wild fires, be burned deliberately by farmers to get rid of old grass, crop residues, and wood tissue, or be burned in order to provide a fertilizer for subsistence farmers. Thus it may be that burning wood and other biomass in domestic stoves causes less emission of the above gases and fewer particulates than occur by the alternative means of decomposition, thereby decreasing not increasing greenhouse gas emissions.

There is anecdotal evidence about methane emissions from rice straw, cow dung, termites and biomass-eating creatures: one sees large areas of vegetation on fire with a corresponding production of particulates and greenhouse gases.

Therefore, until it is proved decisively that burning biomass in domestic stoves makes a net contribution to greenhouse gases, it is misleading to 'encourage people to move up the energy ladder sooner than they might otherwise do'. The policy should be to promote the use of biomass by improving the efficiency of stoves, decreasing their polluting effects and making biomass more readily available.

Yours sincerely,
Keith Openshaw

Yes, I certainly agree with Keith Openshaw about the need to look at the entire fuel cycle when comparing energy systems. The attached figure from my 1992 draft report to the World Bank The Hearth as System Central, illustrates that the carbon in biomass has basically two fates, combustion with emissions of CO: and products of incomplete combustion (PIC) or the route through decay and digestion with emissions of CO: and products of incomplete decay and digestion (here lumped as products of incomplete decomposition - PID). To fully understand the impacts of any change in this system, for example, introduction of an improved stove, it is necessary to compare the conditions of the entire system before and after. If the saved biomass simply lies on the ground to decay and be eaten by termites, for example, there may be little greenhouse gas savings, depending on the amounts and mixtures of PIC and PID before and after.

Indeed, this principal applies to fossil fuel and other energy sources as well. The greenhouse gas emissions at the oil well, tanker, refinery, and distribution depot should be counted as well as those released directly by the kerosene stove, for example.

Although, as Mr Openshaw indicated, much additional work is needed to pin down the actual quantities for a broad range of situations, there are still some important general lessons. Efforts to reduce greenhouse emissions from household biomass stoves need to consider these three caveats about renewability:

I. Just because a biomass fuel cycle has a net zero carbon balance, i.e., represents renewable harvesting, does not mean there is a net zero greenhouse impact.

II. To assure a net zero greenhouse impact for biomass fuel cycles, it is necessary to add a further criterion to renewability that the PIC and PID produced by human harvesting and burning do not exceed that of the system previous to human intervention. 111. In situations where biomass is burned with poor combustion efficiency, movement up the energy ladder to fossil fuels can potentially result in lowered greenhouse emissions, even if the biomass is being harvested renewably.

These caveats stem from two basic principles:

A. Improving combustion and, potentially, decomposition efficiency is critical to reducing the greenhouse impact of household stoves. PIC and PID must be avoided as much as possible, because if carbon is to be put into the atmosphere, CO' is about the best form from a GHG standpoint. Almost every other possible carbon-based PIC gas eventually changes to CO2 and in the meantime has a greater global warming potential.

B. To understand the net greenhouse impact of proposed policies designed to change stoves or fuels, it is necessary to consider both the before and after conditions of the entire fuel carbon cycles to be affected.

These address only greenhouse gases, of course. Concern about other important factors, such as soil fertility, might involve making difficult trade-offs.

As much as possible, improved stoves should be designed to achieve increased combustion efficiency as well as increased overall efficiency. The resultant reduction in PIC will bring both health and greenhouse-gas control benefits.

Technical Enquiries to ITDG

If you have any technical enquiries, ITDG's Technical Enquiry Unit (TEU) should be able to help you. The TEU has extensive contacts within the UK and Europe, and can respond on a wide variety of topics. If your enquiries are about stoves or household energy, then our stove team can also help.

Please send all enquiries to:

The Technical Enquiry Unit
Intermediate Technology
Myson House
Railway Terrace
CV21 3HT

Tel: +44 (0)788 560631
Fax: +44 (0)788 540270
Telex: 317466 ITDG G

Editorial and Production Team

Clare Heyting


Production Manager

Ian Grant



Shyam Sundar


Theme Editor

Peter Young


Project Manager

Mary Breen


Copy Editor

Peter Watts


Energy Unit Manager

Cornelia Sepp


GTZ Editor

Agnes Klingshirn Representative




M. Agumba, J. Baguant, A. Dong, L. Fisher, B. Gobin, I. Grant, A. Harvey, C. Heyting, T. Jones, N. Kamalamma, M. Kamiya, M. Khumalo, A. Klingshirn, J. McAvoy, S. Margret, J. Monk, K. Openshaw, R. Panray Beeharry, H. Staedter, M. Saitharani, S. Sajith, K. Smith, A. Souter, N. Sri Utami, K.M. Sulpya, C. Tager, P.V. Unnikrishnan, M. Waltham, P. Watts.

Contributions to Boiling Point

Contributions are invited for the next two issues of Boiling Point, the themes of which will be:

BP34 - August 1994 - Smoke Removal

BP35 - December 1994 - NGO Impacts

Articles for these issues should reach the Boiling Point office by the 15th June and the 15th October respectively.

Contributions are welcome in the form of articles of not more than 2000 words, including line drawings, photographs, simple graphs, or illustrations, where appropriate. All correspondence should be addressed to Boiling Point, ITDG, Stoves and Household Energy Programme, Myson House, Railway Terrace, Rugby, CV21 3HT.

Back Issues

If you would like a copy of any back issues, please contact us. A detailed index of all Boiling Point articles is also available.

BP 12 - Alternative Fuels; 13 - Safer and Less Smoky Stove; 14 - Kitchens, Pots and Cooking Practices; 15 Stove Progress in Kenya and Sri Lanka; 16 - Muds, Clays and Metals for Stove Making; 17 - Fault Finding and Fixing; 18 - Stove Programmes in the 90s; 19 - Stoves Will Not Sell Themselves; 20 - Non-biomass Stoves; 21 - Stoves, Energy and the Environment; 22 - Other Uses for Stoves; 23 - Measures of Success; 24 - Solar Energy; 25 - Funding for Stove Programmes; 26 - Technology and Design Transfer; 27 - Women, Woodfuel, Work and Welfare; 28 - Biomass Combustion, Chimneys and Hoods; 29 - Household Energy Developments in Southern and East Africa; 30 - Sales and Subsidies; 31 - Clays for Stoves; 32 - Energy for the Household.

Boiling Point is the journal of the Intermediate Technology Development Group's Stove and Household Energy Programme (SHE) and the Household Energy Programme (HEP) of GTZ. It is printed on recycled paper by the Rugby Community Studios Printworks.

Opinions expressed in contributory articles are those of the authors and not necessarily those of the ITDG SHE Programme.

© Intermediate Technology Development Group 1994.

© Bartholomew. Reproduced with permission.


Intermediate Technology enables poor people in the Third World to develop and we technologies and methods which give them more control over their lives and which contribute to the long-tenn development of their communities.

Intermediate Technology it a British charity mainly funded by the Overseas Development Administration.

Intermediate Technology Development Group Ltd., Patron: HRH The Prince of Wales, KG, KT, GCB

Company Reg No. 871954, England. Reg. Charity No. 247257