A report in today’s issue of the magazine “Science” published by the American Association for the Advancement of Science (AAAS) provides a new prespective on the role of fire in Global Climate Change. This publication, in the most prestigious U.S. scientific journal, concludes that the effects of fire on the Earth’s ecosystems and processes, and Global Climate Change “have been underestimated” (Fire in the Earth System. Bowman et al. Science 24 April 2009: 481-484).
The paper estimates that burning, and associated deforestation, by humans contributes about 20% of the human-caused greenhouse effect, and that this percentage could actually be much higher. The international team of 22 authors also report that on an annual basis, fire releases an amount of carbon dioxide that is equal to 50% of the total amount released by the burning of fossil fuels. The authors conclude that role of fire on the earths process is poorly understood, and thus under represented in global climate change computer models.
The findings of this paper again emphasize the role of such processes as fire as feedback mechanisms (http://arewetoast.org/system-feedback-and-tipping-points.html) in which fire releases more carbon dioxide into the atmosphere, which increases climate change resulting in increased regions of drought, which in turn increases wildfires and results in additional releases of carbon dioxide into the atmosphere. While we understand the basic mechanisms of such feedback processes, we lack the baseline data necessary to accurately quantify and refine computer models. Thus feedback processes have generally been treated conservatively in computer models, with the subsequent projections underestimating their impact. It is however, generally acknowledged that such feedback process have the capability to become self-sustaining and thus exceedingly difficult, if not impossible, to control.
The release of carbon dioxide is not the only characteristic of fire that impacts climate change as other greenhouse gases, soot, black carbon, and aerosols are also among the compounds released. Aerosols, for example, reflect incoming solar radiation and thus have a cooling effect. However, their concentration is not generally great, and is short-lived; this their impact is minor. Soot is rapidly deposited on the earths surface and reduces its reflectivity, or albedo, and results in increased warming of the surface. The impact is particularly pronounced in snow, or ice, covered regions where melting may be significantly increased. But, a decrease in albedo of vegetated, or bare soil surfaces may also result in increased evaporation and soil drying. Black carbon is increasingly being found to increase global warming, especially in tropic regions.
The paper recognizes the connectivity between the history of man and fire. Fire has not only been the source of heat and light, but also a “multiplier” of man’s energy, permitting the accomplishment of more work. The quest for firewood has been, and remains today, a major cause of deforestation. It is reported that 25% of the worlds population do not have access to electricity, and that 2.4 billion people depend upon fire for cooking and heating (http://arewetoast.org/social-challenges.html). Thus any understanding, and control, of the impact of fire on Global Climate Change must include the physical, biological, and cultural dynamics of fire.
