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The contribution of biomass to global energy use (1987)
Biomass 21 (1990) 75-81
Short Communication The Contribution of Biomass to Global Energy Use (1987)
ABSTRACT Reasonably accurate estimates of biomass energy use are important, both to emphasise the size of this resource compared with conventional, commercially traded fuels, and for other applications such as energy planning and assessing the environmental impact of energy production and use. Most studies to date have concentrated on particular regions or countries, and many have had to combine data from various authorities. In some cases, these may be traced back to original sources which are already obsolete and often of questionable value. A comprehensive estimate has been made here of biomass energy use compared with conventional energy resources for the year 1987. Data are presented globally and for developed and developing countries. Key words: biomass energy, commercial energy, developed countries, developing countries, global energy.
INTRODUCTION Original and authoritative data on biomass energy use are hard to obtain. This difficulty recurs whether data are required on a global basis, a regional basis, a category basis (e.g. O E C D (Organisation for Economic Co-operation and Development) countries, poorest countries, etc.), or at country or local district level. It is important to have reasonably accurate estimates of biomass energy use in order to emphasise the importance of this resource compared with conventional, commercially traded fuels, both in developing countries (where up to 90% of energy needs may be fulfilled by biomass) and in the industrialised world (where the commercial and domestic use of biomass is also often underestimated). These data should be widely available to energy analysts, planners, environmentalists and all those concerned with supply of energy at both local and national level. 75 Biomass 0144-4565/90/S03.50 - © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
76
J. M. O. Scurlock, D. O. Hall
Very few independent and comprehensive reviews of biomass energy usage have ever been carried out, whether in developed or developing countries. Such surveys are notoriously difficult and time-consuming to carry out accurately. Frequently, the use of biomass in commerce, public institutions and industry is overlooked or inadequately estimated. Most studies have concentrated on particular regions or countries, or been limited to individual cities or villages. Many have had to combine data from various sources, frequently traceable back to original data which are already obsolete and often of questionable value. In this context there is a need to establish a generally agreed figure for biomass energy use in both developed and developing countries, with which regional variations or individual surveys may be compared. Even though such biomass-use figures may change with time, it is imperative to know where we are now, and hopefully what changes are occurring.
ESTIMATION OF BIOMASS ENERGY USE In the estimates presented here (Fig. 1 ), the category 'biomass' has been assumed to include woodfuel, charcoal, agricultural residues, dung, bioethanol and other forms of plant-derived energy. ~Since 1 tonne of charcoal is usually derived from between 6 and 12 tonnes of air-dry wood, estimates of charcoal consumption have been expressed in terms of tonnes of wood equivalent. Data on the use of woodfuel, and agricultural residues and wastes for energy, have been drawn from a wide variety of sources in order to arrive at a per capita figure. This comprehensive approach obviously leads to a greater estimate of the contribution of biomass as a whole to energy supply than is given by official statistics on woodfuel alone. For example, if Food and Agriculture Organisation (FAO) figures for woodfuel only are used to prepare a global estimate,2 the contribution of biomass in developing countries becomes only 14 EJ (cf. 48 EJ in the present study). The following four examples highlight the problems of using official statistics and concentrating only on woodfuel use when attempting to account for total biomass consumption: (i) In India, energy from burning dung and residues doubles the contribution from biomass compared with a consideration of woodfuel alone? ,4 Bhatia 5 recently estimated that two-thirds of India's energy is derived from non-commercial sources. (ii) In China, the weight of available dung and agricultural residues is 2-2 times the weight of woodfuel,a In 1981, the 830 million rural Chinese derived 84% of their energy from biomass (mostly
Nuclear 5% Hydr-
Biomass 14% ~°"
Gas 17%
Oil 32%
WORLD Coal L v
399 EJ (9067 Mtoe) Population = 5.0 billion Energy use per capita = 79.8 GJ (1.81 toe)
,~
Nuclear 5%
/
Hydro £o~
Biomass 3%
Gas 23%
Oil 37%
EVELOPED COUNTRIES . . . . L = 262 EJ (5947 Mtoe); 66% of World Population = 1.2 billion; 24% of World Energy use per capita = 218 GJ (4.96 toe)
Coal 25% Nuclear 1% Hydro 6% "~.
I
Gas Biomass 35%
Coal 28%,
iLOPING COUNTRIES Oil 23*/, I °
I U I A L = 1 3 / E J (3120 Mtoe); 34% of World Population = 3.8 billion; 76% of World Energy use per capita = 36,0 C-,J(0.82 toe)
Fig. 1. Global distribution of energy use (1987). T h e size of the pie diagrams corresponds approximately to the energy use in each part of the world. 2.4.15,16,18,26 Energy conversion factors are as follows: 1.0 EJ = 10 ~s J (approximately equal to 1 Q u a d [USA], i.e. 10 ~-~Btu) 1 Mtoe (million tonnes oil equivalent)= 44 × 106 GJ (44 x 10 ~5J) thus 1 toe = 44 GJ 1 t air-dry biomass (20% moisture) = 15 GJ 1 t woodfuel --- 1.4 m 3 wood 1 t charcoal is derived from 6 - 1 2 t wood
78
J. M. O. Scurlock, D. O. Hall
(iii)
(iv)
agricultural residues), using 328 million tonnes coal equivalent. This is equal to 216 Mtoe (million tonnes of oil equivalent), i.e. about 0.8 t of biomass per capita per annum. 6 Brazil, although a middle-income developing country with a large industrial sector and 72% of the population in 'urban settlements', derives 28% of its energy from biomass. 7,8 This is equivalent to about 0.95 t woodfuel per capita per annum, including 0.16 t year-~ per capita woodfuel equivalent in the form of fuel ethanol. Recent surveys found that biomass accounts for 79% of primary energy consumption in the nine SADCC countries of southern Africa.9,1() For these 70 million people, per capita consumption of woodfuel averages 1-2 t year -1, a figure one-third higher than is estimated from FAO figures for total woodfuel and charcoal consumption in this region. ~
Estimates of per capita biomass energy consumption in the developing countries very widely. Goodman ~z uses a 'very conservative' figure of 0.5 t year -1 for rural populations, while Williams 13 considers the developing country average to be 0-75 t year -l. On a local basis, consumption is usually a function of the availability of fuel, and appears to lie in the range 0.5-2.9 t year-1.~4.15 In the present study, a mean biomass energy consumption figure of 1.0 t year-~ per-capita has been taken for rural areas of the developing countries, and 0"5 t year- ~per capita for urban areas. This assumes that the degree of fuel substitution away from biomass in urban areas is not offset by the energy losses inherent in the increased use of charcoal. Note that these figures include all forms of biomass for all types of energy users, and are expressed in terms of woodfuel equivalent (air-dry weight at 20% moisture, with an energy content of 15 GJ t- 1). After more than a decade of discussion and very little additional good data, we consider these estimates to be realistic and in line with what is available from surveys conducted in the developing countries. To estimate biomass energy consumption for the developed countries, figures for the 23 countries of the O E C D were based on the 12 representative countries reporting to the IEA (International Energy Agency) Forestry Energy Programme. ~6 Data for the USSR and Eastern Europe were taken from WRI (World Resources Institute). 2 The total estimate arrived at by this method is in agreement with Deudney and Flavin. ~7 For the purposes of calculation of non-biomass energy based upon the BP Statistical Review of World Energy,~8 the term 'developed countries'
The contribution of biomass to global energy use
79
includes the OECD countries, USSR and 80% of the other centrally planned economies. The term 'developing countries' includes Latin America, Africa, South and South-East Asia, China, the Middle East and 20% of the centrally planned economies.
DISCUSSION Renewable energy currently contributes about a fifth of the world's energy, with biomass providing 14% and hydro-electricity 6%. Together with the nuclear component of 5%, this means that a quarter of global energy is currently provided by sources which make no net contribution to atmospheric CO 2. However, it should be noted that the relative contribution of both hydro and nuclear depends upon whether they are expressed as the equivalent amount of fossil fuel required to generate the same quantity of electricity] 8 or as delivered electrical energy. 19 To put the contribution of biomass in context, it should be noted that electricity constitutes about 15% of global primary energy supply.~5 The total requirement for biomass energy is unlikely to decrease in the near or medium term in the developing countries unless there is a dramatic switch to commercial fuels by a large share of the population. We do not see evidence of this happening, since urbanisation is accompanied by a continued reliance on biomass fuels (especially charcoal), and the population increase in rural areas remains at a high rate. For example, in Kenya, with an annual population growth rate of 4.0%, the demand for 'firewood' is growing at 3.6% whilst charcoal demand is increasing at 6"7% per annum. 2° By the year 2025, it is predicted that 84% of the world's population will reside in the developing countries, compared with 74% in 1980. 2~ Thus, it is predicted that the demand for biomass in developing countries will increase with population, although the proportion of energy use provided by biomass may remain constant on a global or even a country basis. Most people prefer to have gas, coal or electricity as their energy sources because of convenience and cleanliness, but the majority in the developing countries are unlikely to have access to these fuels in the medium term. They will have to rely on biomass as the fuel of development, and thus it is important that biomass energy be provided in a sustainable manner. Deforestation and devegetation, primarily in connection with land-clearing for agriculture, increase biomass supply in the short term, but can be detrimental to biomass availability and the environment in the longer term. They often result in land degradation as well as addition of CO2 to the atmosphere.
80
J. M. O. Scurlock, D. O. Hall
Biomass, particularly residues from forestry, agriculture and food industries, is widely seen as one of the most promising renewable alternatives for fossil fuel substitution in the European Economic Community (EEC). At present, biomass including municipal solid wastes contributes around 3% of E E C primary energy. 22 The need to control overproduction of food and agricultural support spending is resulting in increasing pressure to develop alternative uses for land, such as production of liquid biofuels or woody energy crops. In the USA, the world's largest single energy market, biofuels supplied nearly 4% of total energy consumption in 1986, almost as much as hydro-electric or nuclear power. 23 Biomass energy is expected to double its contribution to US energy supply by the year 2000. s In considering biomass for energy use only, we have not included its use for other purposes such as construction, fencing, fodder and fibre, which are important in both developed and developing countries. 24 For example in Botswana, the annual wood need per capita for 'bush' (shrub and tree) fencing is 1-5 times the need for woodfuel. 25 Such uses contribute to the pressures of devegetation and thence on the availability of biomass as an energy source. They must be considered when planning for biomass energy use in the future.
REFERENCES 1. Hall, D. O., Barnard, G. W.& Moss, E A., Biomass for Energy in the Developing Countries. Pergamon Press, Oxford, 1982. 2. World Resources 1987. Report by International Institute for Environment and Development/World Resources Institute. Basic Books, New York, 1987. 3. The State of India's Environment 1982. Centre for Science and Environment, 95 Nehru Place, New Delhi, 1982. 4. World Energy Conference Survey of Energy Resources, 1986. World Energy Conference, 34 St James's Street, London SW1A 1HD, 1986. 5. Bhatia, R., Energy demand analysis in developing countries: A review. Energy Journal, 8 (1987) 1-33. 6 Wu Wen & Chen En-Jian, Resolution of China's rural energy requirements. Biomass, 3 (1983) 287-312. 7. Goldemberg, J., Johansson, T. B., Reddy, A. K. N. & Williams, R. H., Energy for a Sustainable World. Wiley Eastern, New Delhi, 1988. 8. Shea, C. D., Renewable Energy," Today's Contribution, Tomorrow's Promise. Worldwatch Paper 81. Worldwatch Institute, Washington, DC, 1988. 9. Kaale, B. K., Energy for rural areas of SADCC countries. Technical and Administrative Unit, SADCC Energy, PO Box 2876, Luanda, Angola, 1988. 10. Munslow, B., Katerere, Y., Ferf, A. & O'Keefe, P., The Fuelwood Trap: A Study of the SADCC Region. Earthscan, London, 1988.
The contribution of biomass to global energy use
81
11. FAO Yearbook of Forest Products 1985. UN Food and Agriculture Organisation, Via delle Terme de Caracalla, 00100 Rome, Italy, 1986. 12. Goodman, G., Biomass energy in developing countries. Ambio, 16 ( 1987 ) 111-19. 13. Williams, R. H., Potential roles for bioenergy in an energy efficient world. Ambio, 14 (1987) 201-9. 14. Barnard, G. W., Woodfuel in developing countries. In Biomass: Regenerable Energy, ed. D. O. Hall & R. P. Overend. John Wiley, Chichester, 1987, pp. 349-66. 15. Our Common Future. Report by World Commission on Environment and Development. Oxford University Press, Oxford, 1987. 16. Renewable Sources of Energy. International Energy Agency (lEA). Organisation for Economic Co-operation and Development (OECD), 2 Rue Andre-Pascal, Paris 75775, 1987. 17. Deudney, D. & Flavin, C., Renewable Energy: The Power to Choose. Norton, New York, 1983. 18. BP Statistical Review of World Energy 1987. British Petroleum Company, Moor Lane, London EC2Y 9BU, 1988. 19. Energy in Sweden 1987. National Energy Administration, Stockholm, 1987. 20. Opole, M., Improved charcoal stoves programme, Kenya. In The Greening of Aid: Sustainable Livelihoods in Practice, ed. C. Conroy & M. Litvinoff. Earthscan Publications, London, 1988, pp. 118-23. 21. Demeny, P., Population change: Global trends and implications. In Resources and World Development, ed. D. J. McLaren & B. J. Skinner. John Wiley, Chichester, 1987, pp. 29-48. 22. Molle, J. F., Biomass for energy in Europe: An overview. In Euroforum New Energies; Proc. Int. Symp., Saarbrucken, Vol. 1. Commission of the European Communities, Brussels, H.S. Stephens Publ., Bedford, UK, 1988, pp. 19-25. 23. Klass, D. L., The US biofuels industry. In Energy from Biomass and Wastes XIII. Institute of Gas Technology, Chicago, 1989, pp. 1-40. 24. Hall, D. O. & de Groot, P. J., Biomass for fuel and food: A parallel necessity. In Advances in Solar Energy, ed. W. Boer. Plenum Press, New York, 1987, Vol. 3, pp. 439-76 and Vol. 4, pp. 1-90. 25. Tietema, T. & Geche, J., A quantitative determination of the amount of wood needed for the erection of bush fences around arable fields in Botswana. Forestry Association of Botswana Journal ( 1987) 19-25. Forestry Association of Botswana, PO Box 2088, Garborone. 26. World Bank, World Development Report 1988. Oxford University Press, Oxford, 1988. J. M. O. Scurlock & D. O. Hall Division of Biosphere Sciences, King's College London, Carnpden Hill Road, London W8 7AH, UK (Received 28 December 1988; revisedversion received 20 June 1989; accepted 26 June 1989)
Short Communication The Contribution of Biomass to Global Energy Use (1987)
ABSTRACT Reasonably accurate estimates of biomass energy use are important, both to emphasise the size of this resource compared with conventional, commercially traded fuels, and for other applications such as energy planning and assessing the environmental impact of energy production and use. Most studies to date have concentrated on particular regions or countries, and many have had to combine data from various authorities. In some cases, these may be traced back to original sources which are already obsolete and often of questionable value. A comprehensive estimate has been made here of biomass energy use compared with conventional energy resources for the year 1987. Data are presented globally and for developed and developing countries. Key words: biomass energy, commercial energy, developed countries, developing countries, global energy.
INTRODUCTION Original and authoritative data on biomass energy use are hard to obtain. This difficulty recurs whether data are required on a global basis, a regional basis, a category basis (e.g. O E C D (Organisation for Economic Co-operation and Development) countries, poorest countries, etc.), or at country or local district level. It is important to have reasonably accurate estimates of biomass energy use in order to emphasise the importance of this resource compared with conventional, commercially traded fuels, both in developing countries (where up to 90% of energy needs may be fulfilled by biomass) and in the industrialised world (where the commercial and domestic use of biomass is also often underestimated). These data should be widely available to energy analysts, planners, environmentalists and all those concerned with supply of energy at both local and national level. 75 Biomass 0144-4565/90/S03.50 - © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
76
J. M. O. Scurlock, D. O. Hall
Very few independent and comprehensive reviews of biomass energy usage have ever been carried out, whether in developed or developing countries. Such surveys are notoriously difficult and time-consuming to carry out accurately. Frequently, the use of biomass in commerce, public institutions and industry is overlooked or inadequately estimated. Most studies have concentrated on particular regions or countries, or been limited to individual cities or villages. Many have had to combine data from various sources, frequently traceable back to original data which are already obsolete and often of questionable value. In this context there is a need to establish a generally agreed figure for biomass energy use in both developed and developing countries, with which regional variations or individual surveys may be compared. Even though such biomass-use figures may change with time, it is imperative to know where we are now, and hopefully what changes are occurring.
ESTIMATION OF BIOMASS ENERGY USE In the estimates presented here (Fig. 1 ), the category 'biomass' has been assumed to include woodfuel, charcoal, agricultural residues, dung, bioethanol and other forms of plant-derived energy. ~Since 1 tonne of charcoal is usually derived from between 6 and 12 tonnes of air-dry wood, estimates of charcoal consumption have been expressed in terms of tonnes of wood equivalent. Data on the use of woodfuel, and agricultural residues and wastes for energy, have been drawn from a wide variety of sources in order to arrive at a per capita figure. This comprehensive approach obviously leads to a greater estimate of the contribution of biomass as a whole to energy supply than is given by official statistics on woodfuel alone. For example, if Food and Agriculture Organisation (FAO) figures for woodfuel only are used to prepare a global estimate,2 the contribution of biomass in developing countries becomes only 14 EJ (cf. 48 EJ in the present study). The following four examples highlight the problems of using official statistics and concentrating only on woodfuel use when attempting to account for total biomass consumption: (i) In India, energy from burning dung and residues doubles the contribution from biomass compared with a consideration of woodfuel alone? ,4 Bhatia 5 recently estimated that two-thirds of India's energy is derived from non-commercial sources. (ii) In China, the weight of available dung and agricultural residues is 2-2 times the weight of woodfuel,a In 1981, the 830 million rural Chinese derived 84% of their energy from biomass (mostly
Nuclear 5% Hydr-
Biomass 14% ~°"
Gas 17%
Oil 32%
WORLD Coal L v
399 EJ (9067 Mtoe) Population = 5.0 billion Energy use per capita = 79.8 GJ (1.81 toe)
,~
Nuclear 5%
/
Hydro £o~
Biomass 3%
Gas 23%
Oil 37%
EVELOPED COUNTRIES . . . . L = 262 EJ (5947 Mtoe); 66% of World Population = 1.2 billion; 24% of World Energy use per capita = 218 GJ (4.96 toe)
Coal 25% Nuclear 1% Hydro 6% "~.
I
Gas Biomass 35%
Coal 28%,
iLOPING COUNTRIES Oil 23*/, I °
I U I A L = 1 3 / E J (3120 Mtoe); 34% of World Population = 3.8 billion; 76% of World Energy use per capita = 36,0 C-,J(0.82 toe)
Fig. 1. Global distribution of energy use (1987). T h e size of the pie diagrams corresponds approximately to the energy use in each part of the world. 2.4.15,16,18,26 Energy conversion factors are as follows: 1.0 EJ = 10 ~s J (approximately equal to 1 Q u a d [USA], i.e. 10 ~-~Btu) 1 Mtoe (million tonnes oil equivalent)= 44 × 106 GJ (44 x 10 ~5J) thus 1 toe = 44 GJ 1 t air-dry biomass (20% moisture) = 15 GJ 1 t woodfuel --- 1.4 m 3 wood 1 t charcoal is derived from 6 - 1 2 t wood
78
J. M. O. Scurlock, D. O. Hall
(iii)
(iv)
agricultural residues), using 328 million tonnes coal equivalent. This is equal to 216 Mtoe (million tonnes of oil equivalent), i.e. about 0.8 t of biomass per capita per annum. 6 Brazil, although a middle-income developing country with a large industrial sector and 72% of the population in 'urban settlements', derives 28% of its energy from biomass. 7,8 This is equivalent to about 0.95 t woodfuel per capita per annum, including 0.16 t year-~ per capita woodfuel equivalent in the form of fuel ethanol. Recent surveys found that biomass accounts for 79% of primary energy consumption in the nine SADCC countries of southern Africa.9,1() For these 70 million people, per capita consumption of woodfuel averages 1-2 t year -1, a figure one-third higher than is estimated from FAO figures for total woodfuel and charcoal consumption in this region. ~
Estimates of per capita biomass energy consumption in the developing countries very widely. Goodman ~z uses a 'very conservative' figure of 0.5 t year -1 for rural populations, while Williams 13 considers the developing country average to be 0-75 t year -l. On a local basis, consumption is usually a function of the availability of fuel, and appears to lie in the range 0.5-2.9 t year-1.~4.15 In the present study, a mean biomass energy consumption figure of 1.0 t year-~ per-capita has been taken for rural areas of the developing countries, and 0"5 t year- ~per capita for urban areas. This assumes that the degree of fuel substitution away from biomass in urban areas is not offset by the energy losses inherent in the increased use of charcoal. Note that these figures include all forms of biomass for all types of energy users, and are expressed in terms of woodfuel equivalent (air-dry weight at 20% moisture, with an energy content of 15 GJ t- 1). After more than a decade of discussion and very little additional good data, we consider these estimates to be realistic and in line with what is available from surveys conducted in the developing countries. To estimate biomass energy consumption for the developed countries, figures for the 23 countries of the O E C D were based on the 12 representative countries reporting to the IEA (International Energy Agency) Forestry Energy Programme. ~6 Data for the USSR and Eastern Europe were taken from WRI (World Resources Institute). 2 The total estimate arrived at by this method is in agreement with Deudney and Flavin. ~7 For the purposes of calculation of non-biomass energy based upon the BP Statistical Review of World Energy,~8 the term 'developed countries'
The contribution of biomass to global energy use
79
includes the OECD countries, USSR and 80% of the other centrally planned economies. The term 'developing countries' includes Latin America, Africa, South and South-East Asia, China, the Middle East and 20% of the centrally planned economies.
DISCUSSION Renewable energy currently contributes about a fifth of the world's energy, with biomass providing 14% and hydro-electricity 6%. Together with the nuclear component of 5%, this means that a quarter of global energy is currently provided by sources which make no net contribution to atmospheric CO 2. However, it should be noted that the relative contribution of both hydro and nuclear depends upon whether they are expressed as the equivalent amount of fossil fuel required to generate the same quantity of electricity] 8 or as delivered electrical energy. 19 To put the contribution of biomass in context, it should be noted that electricity constitutes about 15% of global primary energy supply.~5 The total requirement for biomass energy is unlikely to decrease in the near or medium term in the developing countries unless there is a dramatic switch to commercial fuels by a large share of the population. We do not see evidence of this happening, since urbanisation is accompanied by a continued reliance on biomass fuels (especially charcoal), and the population increase in rural areas remains at a high rate. For example, in Kenya, with an annual population growth rate of 4.0%, the demand for 'firewood' is growing at 3.6% whilst charcoal demand is increasing at 6"7% per annum. 2° By the year 2025, it is predicted that 84% of the world's population will reside in the developing countries, compared with 74% in 1980. 2~ Thus, it is predicted that the demand for biomass in developing countries will increase with population, although the proportion of energy use provided by biomass may remain constant on a global or even a country basis. Most people prefer to have gas, coal or electricity as their energy sources because of convenience and cleanliness, but the majority in the developing countries are unlikely to have access to these fuels in the medium term. They will have to rely on biomass as the fuel of development, and thus it is important that biomass energy be provided in a sustainable manner. Deforestation and devegetation, primarily in connection with land-clearing for agriculture, increase biomass supply in the short term, but can be detrimental to biomass availability and the environment in the longer term. They often result in land degradation as well as addition of CO2 to the atmosphere.
80
J. M. O. Scurlock, D. O. Hall
Biomass, particularly residues from forestry, agriculture and food industries, is widely seen as one of the most promising renewable alternatives for fossil fuel substitution in the European Economic Community (EEC). At present, biomass including municipal solid wastes contributes around 3% of E E C primary energy. 22 The need to control overproduction of food and agricultural support spending is resulting in increasing pressure to develop alternative uses for land, such as production of liquid biofuels or woody energy crops. In the USA, the world's largest single energy market, biofuels supplied nearly 4% of total energy consumption in 1986, almost as much as hydro-electric or nuclear power. 23 Biomass energy is expected to double its contribution to US energy supply by the year 2000. s In considering biomass for energy use only, we have not included its use for other purposes such as construction, fencing, fodder and fibre, which are important in both developed and developing countries. 24 For example in Botswana, the annual wood need per capita for 'bush' (shrub and tree) fencing is 1-5 times the need for woodfuel. 25 Such uses contribute to the pressures of devegetation and thence on the availability of biomass as an energy source. They must be considered when planning for biomass energy use in the future.
REFERENCES 1. Hall, D. O., Barnard, G. W.& Moss, E A., Biomass for Energy in the Developing Countries. Pergamon Press, Oxford, 1982. 2. World Resources 1987. Report by International Institute for Environment and Development/World Resources Institute. Basic Books, New York, 1987. 3. The State of India's Environment 1982. Centre for Science and Environment, 95 Nehru Place, New Delhi, 1982. 4. World Energy Conference Survey of Energy Resources, 1986. World Energy Conference, 34 St James's Street, London SW1A 1HD, 1986. 5. Bhatia, R., Energy demand analysis in developing countries: A review. Energy Journal, 8 (1987) 1-33. 6 Wu Wen & Chen En-Jian, Resolution of China's rural energy requirements. Biomass, 3 (1983) 287-312. 7. Goldemberg, J., Johansson, T. B., Reddy, A. K. N. & Williams, R. H., Energy for a Sustainable World. Wiley Eastern, New Delhi, 1988. 8. Shea, C. D., Renewable Energy," Today's Contribution, Tomorrow's Promise. Worldwatch Paper 81. Worldwatch Institute, Washington, DC, 1988. 9. Kaale, B. K., Energy for rural areas of SADCC countries. Technical and Administrative Unit, SADCC Energy, PO Box 2876, Luanda, Angola, 1988. 10. Munslow, B., Katerere, Y., Ferf, A. & O'Keefe, P., The Fuelwood Trap: A Study of the SADCC Region. Earthscan, London, 1988.
The contribution of biomass to global energy use
81
11. FAO Yearbook of Forest Products 1985. UN Food and Agriculture Organisation, Via delle Terme de Caracalla, 00100 Rome, Italy, 1986. 12. Goodman, G., Biomass energy in developing countries. Ambio, 16 ( 1987 ) 111-19. 13. Williams, R. H., Potential roles for bioenergy in an energy efficient world. Ambio, 14 (1987) 201-9. 14. Barnard, G. W., Woodfuel in developing countries. In Biomass: Regenerable Energy, ed. D. O. Hall & R. P. Overend. John Wiley, Chichester, 1987, pp. 349-66. 15. Our Common Future. Report by World Commission on Environment and Development. Oxford University Press, Oxford, 1987. 16. Renewable Sources of Energy. International Energy Agency (lEA). Organisation for Economic Co-operation and Development (OECD), 2 Rue Andre-Pascal, Paris 75775, 1987. 17. Deudney, D. & Flavin, C., Renewable Energy: The Power to Choose. Norton, New York, 1983. 18. BP Statistical Review of World Energy 1987. British Petroleum Company, Moor Lane, London EC2Y 9BU, 1988. 19. Energy in Sweden 1987. National Energy Administration, Stockholm, 1987. 20. Opole, M., Improved charcoal stoves programme, Kenya. In The Greening of Aid: Sustainable Livelihoods in Practice, ed. C. Conroy & M. Litvinoff. Earthscan Publications, London, 1988, pp. 118-23. 21. Demeny, P., Population change: Global trends and implications. In Resources and World Development, ed. D. J. McLaren & B. J. Skinner. John Wiley, Chichester, 1987, pp. 29-48. 22. Molle, J. F., Biomass for energy in Europe: An overview. In Euroforum New Energies; Proc. Int. Symp., Saarbrucken, Vol. 1. Commission of the European Communities, Brussels, H.S. Stephens Publ., Bedford, UK, 1988, pp. 19-25. 23. Klass, D. L., The US biofuels industry. In Energy from Biomass and Wastes XIII. Institute of Gas Technology, Chicago, 1989, pp. 1-40. 24. Hall, D. O. & de Groot, P. J., Biomass for fuel and food: A parallel necessity. In Advances in Solar Energy, ed. W. Boer. Plenum Press, New York, 1987, Vol. 3, pp. 439-76 and Vol. 4, pp. 1-90. 25. Tietema, T. & Geche, J., A quantitative determination of the amount of wood needed for the erection of bush fences around arable fields in Botswana. Forestry Association of Botswana Journal ( 1987) 19-25. Forestry Association of Botswana, PO Box 2088, Garborone. 26. World Bank, World Development Report 1988. Oxford University Press, Oxford, 1988. J. M. O. Scurlock & D. O. Hall Division of Biosphere Sciences, King's College London, Carnpden Hill Road, London W8 7AH, UK (Received 28 December 1988; revisedversion received 20 June 1989; accepted 26 June 1989)