Atmospheric implications of burning forests

Friday 30 April 1993

Global Biomass Burning -- Atmospheric, Climatic, and Biospheric Implications Edited by: Joel S Levine Publisher: The MIT Press, Cambridge, Massachusetts Price: US $75

MOTIVATED by the need for a holistic understanding of the impact of human activity on the earth's natural phenomena, scientists in the last decade have been studying the earth as an entire system, focussing their attention on large-scale physical and biotic (related to living things) interactions. The pursuit of this understanding has posed two questions: How are changes in surface vegetation cover interacting with regional climate? How are changing land cover patterns and land usages altering the composition of the atmosphere?

A significant human influence on the planet's atmosphere and climate is evident in the phenomenon of global warming. Among the factors contributing to the warming of the earth, an important one is the burning of biomass -- forests, grasslands and agricultural fields after a harvest.

Despite awareness of problems caused by biomass burning, little quantitative information is available, as seems evident after going through Global Biomass Burning -- Atmospheric, Climatic, and Biospheric Implications. The book contains 63 chapters, written by 158 scientists, and is a convenient overview of the latest knowledge about biomass burning and its impact on the global atmosphere.

The argument that biomass burning just returns to the atmosphere carbon dioxide and water removed earlier by plants -- viewed in a geological time scale this is merely carbon dioxide recycling -- is wrong, particularly since the gas is not removed because of lack of regrowth, as in deforestation of tropical forests. Carbon dioxide is the largest contributor to the greenhouse effect.

Annually, 5 per cent of the earth's land surface experiences biomass burning. In 1990, the atmospheric carbon concentration was 352 ppm (parts per million) or 745 gigatonnes (1 gigatonne = 10 9 tonnes). In 2100, it will be 688 ppm or 1,450 gigatonnes if current levels of deforestation persist, and 605 ppm (1276 gigatonnes) if deforestation is checked. Other gases emitted when biomass is burnt include carbon monoxide; methane and other non-methane hydrocarbons; methyl chloride; oxides of nitrogen and various partially oxidised organic compounds such as organic acids. The ammonia and nitric acid released annually from biomass burning, particularly in wetlands, is estimated to be 5.3 million tonnes and 1.5 million tonnes, respectively. These compounds contribute significantly to the greenhouse effect.

Biomass burning also causes a haze of aerosols that remains for days, and though quantitative estimates of the particulate matter in it are still uncertain, the regional effects of such a pall can be both complex and extreme. Most damaging is the ability of the particulate matter to form cloud condensation nuclei (CNN). Because the number of CNN are steadily increasing and given the constant amount of available water, smaller droplets are formed, which result in whiter clouds that reflect more sunlight back to space, but are less likely to produce rain. This can disturb the earth's heat and water balance.

Biomass burning produces charcoal and considerably alters the terrestrial chemical composition by converting into gas the sulphur and nitrogen in the soil and thus disrupting the nutrient cycles. It also produces ozone and may be responsible for about half the greenhouse warming due to increase in tropospheric ozone.
Consumption culture Today, the very words "global warming" are considered a harbinger of impending doom and destruction. This is a result of a consumption culture that was based on an idea, dating back to Aristotle, that nothing in nature had a value on its own, but were all merely "resources" to be used by humans as they felt fit.

But the development of science since the 19th century changed our perception of our importance in the scheme of things. As our cosmic significance declined, the earth's finite nature became more apparent and our capacity to damage it more alarming. It is against this backdrop of changing perceptions that we have to look at resources and their exploitation.

"Development" is ultimately the exploitation of the natural resources in such a way that energy flows from the natural processes are switched to technological processes that stabilise human society. There are obvious fallouts of such development. Carbon dioxide is the largest contributor to global warming and about 80 per cent of it results from burning of fossil fuels, with USA and the Commonwealth of Independent States (the former USSR) accounting for half of it. Most of the remaining 20 per cent comes from deforestation, to which Brazil is the largest contributor.

Deforestation results directly from "civilised, modern" society's gluttony. The annual per capita beef consumption in USA rose from 26 kg in the 1940s to 53 kg in 1972. There was a concomitant rise in such ailments as heart attacks and atherosclerosis. Considering the amount of grain needed to produce this meat in these days of factory farming, the large-scale deforestation that is taking place is easily explained.

Worldwide emission of carbon from biomass burning is estimated to range between 3,000 million tonnes and 6,200 million tonnes annually. And a major contribution to this is from the burning of forests in the tropics, induced by Northern overconsumption.

Global Biomass Burning, which is the outcome of a Chapman conference of the American Geophysical Union, jars you out of an anthropocentric world view. It also contains contributions from the International Geosphere-Biosphere Programme: A Study of Global Change; the International Global Atmospheric Chemistry Project, and the US Environmental Protection Agency. The book's rich historical and geographical coverage is enhanced by the advanced research methods it employs, such as Landsat imagery, simulation studies and model-building. It touches on different sampling techniques and chemical analysis of the phenomena. There are also concrete suggestions about policy implications for managing biomass burning to mitigate global climate change.

But for some disputable figures and its overly technical nature, Global Biomass Burning is interesting reading and should be particularly useful for scientists and activists.

---Bhanusingha Ghosh is a senior research fellow at the School of Life Sciences, Jawaharlal Nehru University.

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