JOHANN G. GOLDAMMER
describes how global warming and forest wildfire disasters may become locked in a vicious circle
Many types of forest, historically adapted to outbreaks of fire from both natural and human sources, are now becoming increasingly vulnerable to it. This is the result of changes in demography and land use, and the cumulative effects of the disturbances brought about by humanity.
Fire is an important recurrent natural phenomenon in all vegetation zones, ranging from the tropics to the northern circumpolar conifer forests. In some ecosystems it maintains the dynamic equilibrium responsible for high biodiversity and economic productivity. In others, such as lowland and mountain rain forests, it destroys the forest cover and leads to long-term site degradation. But, in most areas of the world, wildfires burning under extreme weather conditions have severely damaged economies and human health and safety and caused major disasters.
Extended wildfires in the Indonesian and Malaysian provinces on the island of Borneo during the drought of 1982-1983 - caused by the El Niño-Southern Oscillation (ENSO) - burned more that 5 million hectares of forest and agricultural land, at a total cost of around $9 billion. The effects of similar fire episodes in 1997-1998 in Indonesia, Brazil and Central America have not yet been fully assessed but preliminary estimates suggest that the total value of damage to health, industrial production, tourism, agriculture, timber and other forest products, biodiversity, and air, ground and sea transport - together with the cost of fire-fighting - exceeds $5 billion.
Australia's Ash Wednesday Fires of 1983 - also linked to the extreme ENSO drought of 1982-1983 - killed 75 people and nearly 300,000 sheep and cattle, and destroyed 2,539 houses. In 1987 wildfires in the People's Republic of China killed 221 people (mainly as a result of high carbon monoxide concentrations in forest villages), made 50,000 homeless and burned 1.3 million hectares of mountain forest. Indeed between 1950 and 1990 a total of 4,137 people were killed in forest fires in China. The last major fires in central Eurasia were in Mongolia, where 10.7 million hectares of forest and steppe vegetation were burned in 1996, followed by a further 12.4 million hectares in 1997.
Smoke pollution from burning vegetation sometimes causes death and illness. The most serious pollution problems in the 1980s and 1990s have been in the Amazon Basin and in Southeast Asia. The most recent large smog episodes in Southeast Asia were in 1991, 1994 and 1997 when land-use fires and uncontrolled wildfires in Indonesia and neighbouring countries created a layer of smog which covered a wide region for several weeks. A study on asthma attacks in children showed that high concentrations of carbon monoxide, nitrogen dioxide and inhalable suspended particulate matter, all generated by the fires, were to blame - the smog of September 1997 caused the worst smoke pollution ever recorded in the region.
Wildfires in vegetation contaminated with radioactivity cause uncontrollable releases of such radionuclides as caesium 137C, strontium 90 and plutonium 239. This happened, for instance, in the severely contaminated region near the Chernobyl nuclear power plant.
Vegetation fires also produce emissions that affect the composition and functioning of the global atmosphere - and interact with those from burning fossil fuels and other technological sources which are the major cause of human-induced climate change. Recent estimates suggest that some
2 to 5 billion tonnes of carbon stored in vegetation may be released annually by fires and other burning of plant biomass including biofuels. Most of this, however, is sequestered by regrowth of vegetation.
The net emission of carbon into the atmosphere from deforestation has been estimated to be in the range of 1 to 1.5 billion tonnes per year. Savannah fires, land-use changes, shifting agriculture, agricultural waste burning and fuelwood consumption all make important contributions to the total worldwide burning of biomass, and are included in these figures.
Emissions from tropical vegetation fires are dominated by carbon dioxide (CO2), but products of incomplete combustion that play important roles in atmospheric chemistry and climate are also emitted: these include nitrogen oxide, carbon monoxide, methane and reactive hydrocarbons, which influence the concentrations of ozone and hydroxyl radicals and thus the oxidation efficiency of the atmosphere. These particularly affect tropical regions during the dry seasons - August to November in the southern hemisphere and January to May in the northern one; they are manifested in strongly enhanced tropospheric ozone concentrations, which extend throughout regions regularly affected by forest conversion and dry forest burning in Brazil, by savannah fires in southern Africa, and by land-use fires in Southeast Asia. Concentrations of methyl chloride and methyl bromide - which, with methane, play a significant role in stratospheric ozone chemistry - are also strongly dominated by vegetation fires.
The most critical fires occur during extreme droughts, and the El Niño-induced climate variability is usually closely connected with increased fire activity and damage. Droughts are expected to be more frequent in a world where the atmosphere contains twice as much CO2 as it did at the beginning of the industrial revolution, and which - the Canadian Climate Centre's Global Circulation Model predicts - will be 3.5oC warmer. The fire season will grow longer, leading to more large, high-intensity wildfires. Canadian scientists predict the season will increase by an average of some 30 days a year, with the area of their country's boreal forests that burns each year increasing by a fifth. Increased fire activity will also be particularly critical for the larch forests of eastern Siberia, where it is expected to cause large-scale losses.
Drought and fire may also release carbon from the peat bogs and swamps of the boreal zone. Between 66 and 98 billion tonnes of carbon are estimated to be stored in living and dead plant biomass in the global boreal forest area. Thus more fires, arising from more frequent and intense drought, may produce an additional pulse of CO2 to the atmosphere, acting as a feedback loop in global warming. Global climate models also predict more frequent and more intense El Niño events in a warmer world, causing drought, fire and socio-economic problems in many parts of the planet.
In the past, forests have been an important buffer against climate change because of the way they absorb carbon. But warming, bringing more frequent drought and fires, may affect the balance of the global carbon pool and release extra CO2 into the atmosphere.
Urgent action is required at all levels of politics and policy, strategy development and management, with action plans being based on fundamental research. Fire management strategies - including preparedness and early warning - cannot be generalized because fire has such multidirectional and multidimensional effects in the different vegetation zones and ecosystems and because many different cultural, social and economic factors are involved. So UNEP faces a challenging task in coordinating the United Nations response to fire, and depends on contributions from such interdisciplinary science programmes as the International Geosphere-Biosphere Programme, and from other United Nations efforts, like the International Decade of Natural Disaster Reduction and the International Tropical Timber Organization, the World Meteorological Organization's Global Atmospheric Watch Programme and the World Health Organization's Guidelines Project on Health and Forest Fire Events.
Dr. Johann Georg Goldammer leads the Fire Ecology Research Group at the Max Planck Institute for