Traditional biomass fuels such as wood, charcoal, crop residues and animal dungremain the most common sources of household energy in most of the developing world. They account for about a third of all energy consumption in developing countries
as a whole, and nearly 90 per cent in some of the least developed countries (Kartha and Larson 2000). Coal is still used in many
households, particularly in China. Traditionally, these solid fuels have been burned with poor combustion efficiency under
poorly ventilated conditions, such as the three-stone fire inside a hut. This has resulted in a host of problems, including damage to human health from indoor air pollution (Figure 3), pressure on natural ecosystems from fuel gathering, and excessive time spent on fuel collection by the poor at the expense of time for income generation, education, childcare and so on.
In many developing countries, genderascribed roles entrenched within the social and cultural fabric mean that women and girls are
often responsible for fuel collection and cooking. Women may spend as much as three to seven hours per day by the cooking fire,
exposed to smoke, often with young children nearby (ESMAP 2004). The potential health impacts of health-damaging pollutants from burning solid fuels are compounded by the constant proximity of the users to the source. It is possible to burn biomass (wood and agricultural residues) quite cleanly, producing mostly carbon dioxide and water, but such conditions are difficult to achieve with small-scale inexpensive stoves. Studies in India and China, for example, show that the percentage of fuel carbon fully burned to carbon dioxide is typically only 90 per cent, with some fuel/stove combinations only achieving 80 per cent. The remaining 10 to 20 per cent is diverted into products of incomplete combustion — primarily carbon monoxide, but including benzene, 1,3-butadiene, formaldehyde, polyaromatic hydrocarbons, and many other compounds posing health hazards (Smith and others 2000).
Household coal use can present additional hazards because of the intrinsic toxic contaminants in some coals, including sulphur, arsenic, fluorine, mercury, and selenium. Combined with the low energy efficiency of burning devices, the result is large emissions per unit of useful energy delivered. The best indicator of the health hazard of combustion smoke is thought to be small particles, which contain many chemicals. Since the mid-1980s, many epidemiological studies have examined a range of health effects from indoor air pollution due to solid fuel use. Various health effects have been found, including:
● acute lower respiratory infections in young children, the primary cause of childhood mortality worldwide and the disease responsible for the most lost life years in the world. Indoor air pollution seems to play an important role, although the main risk factor is malnutrition;
● chronic obstructive pulmonary disease, such as chronic bronchitis and emphysema, particularly in adult women who have cooked over unvented solid fuel stoves for many years; and
● lung cancer, mainly from coal smoke. It seems that young children are twice as likely to contract acute lower respiratory infections and women are three times more likely to suffer from chronic bronchitis if exposed to indoor air pollution from solid
fuels (Smith and others 2004). Effects probably occur in men and school-age children as well (although both these groups
typically spend less time inside the home) but few studies have been conducted.
There is also growing evidence of other health effects from indoor air pollution – including tuberculosis, cataracts, several other cancers, low birth-weight, stillbirth, and heart disease. Amongst the most convincing health studies are those that document an improvement in health associated with a
reduction in pollution levels. Two studies conducted in south China showed a significant reduction in lung cancer and chronic obstructive pulmonary disease due to the introduction of improved coal stoves in the late 1970s (Lan and others 2002,
Chapman and others 2005). As development progresses, households tend to move to cleaner fuels (Figure 4). This process of moving up the so-called energy ladder is a slow one and households often shift only selected cooking tasks to cleaner but more expensive fuels at first. The recent increase in crude oil prices and the reduction of fuel subsidies for the poor in countries such
as Indonesia and India could force households back down the energy ladder, to more use of biomass fuels.
It is perhaps surprising that biomass stoves contribute to global warming even when the biomass is harvested as a renewable resource and carbon dioxide emissions from the combustion process are offset by the absorption of carbon dioxide during re-growth. One reason is that biomass, particularly wood, is not always harvested renewably, from sources that regrow. Another is that some products of incomplete combustion – particularly methane and black carbon particles – are even more powerful greenhouse pollutants than carbon dioxide, and therefore have higher global warming potential. Thus, although biomass fuel used on traditional stoves can sometimes be carbon neutral, the process is not greenhouse gas (GHG) neutral unless the biomass fuel is burnt efficiently and completely.
Depending on assumptions and global warming potentials of the different pollutants involved, improving biomass stoves can
achieve a double benefit in the form of lower GHG emissions and reduced ill-health. Even shifting to clean-burning fossil fuels
could be considered a GHG-reduction measure in places where wood is not harvested renewably, because it reduces emissions of methane and black carbon, as well as of CO2 (Smith and others 2000). This is not to say that the growing risk of global climate change is due to the stoves of the poor.
To blunt global warming, it is the world’s use of fossil fuels that needs to be addressed. However, investments in better energy technologies for the poor offer the possibility of substantial and important benefits aside from GHG reductions, including reduced health risks, saving of women’s time, reduced resource consumption, and other local benefits.