Global Biomass Burning major cause of Global Warming
by John L. Roeder
Two threatening consequences of changes in atmospheric composition due to human activities are global warming and stratospheric ozone depletion. Joel S. Levine of NASA's Langley Research Center, speaking at a plenary session of the American Association of Physics Teachers in College Park, MD, on 7 August 1996, saw these effects as rivaled only by those of photosynthetic organisms three million years ago. In particular, he looked at the effects of biomass burning in his address entitled "Earth on Fire: The Atmospheric, Climatic, and Biospheric Implications of Global Burning."
Though some greenhouse effect is necessary for life to live comfortably on earth -- without it the average temperature would be 0o F, he said -- there is now concern that a predicted temperature increase (based on 30 computer climate models) between 2 and 4o C by 2050 would subject planet Earth to the largest rate of temperature increase it has ever known. The resulting increase in sea level (between 30 and 110 cm) could displace 250 million people by flooding. At the same time, the stratosphere would cool by 20 o C and become depleted of its ozone even more easily.
Levine showed the traditional graph showing annual oscillations about a constantly increasing concentration of carbon dioxide, the most abundant greenhouse gas, in the atmosphere. When he superimposed on this a graph of tons of carbon emitted from fossil fuel use, though, it became clear that fossil fuel use decoupled from carbon dioxide concentration in early 1980s. Was this due to saturation of carbon dioxide sinks? or to another carbon dioxide source? Levine then presented a comparison of digitized satellite photos separated by 10 days, which showed a high density of fires in equatorial Africa where wooded savannas occur. According to Levine, these fires are human initiated and account for one third of global warming. The same effect is also clearly delineated for boreal forest in Canada.
Levine reported that the National Academy of Sciences estimates that 0.01 % of the world's land area burns each year. In contrast, NASA estimates this figure to be 1% (3% in 1987). Biomass is 45% carbon, 50% water, the remainder trace substances including methane and sulfur dioxide. NASA's MAPS program shows the highest atmospheric carbon monoxide in equatorial South America and Africa, not in industrial areas (and high tropospheric ozone just west of equatorial Africa). Although some of this carbon dioxide is reabsorbed from the atmosphere when savanna grassland regrows, this does not apply to the other gases emitted into the atmosphere by the burning, including ozone-destroying methyl bromide.
Levine cited Joshua Lederberg's warning that global biomass burning would also release new viruses into the atmosphere. According to Levine, a new NASA global monitoring satellite is proposed to map global biomass burning more completely.
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