Wildfires have historically been viewed as unstructured fires occurring in the wilderness, forest and arid zones, causing massive destruction to life, property and natural vegetation. However, they are also an important part of the carbon and climatic cycles. Though taken in isolation, each conflagration can cause massive human, economic and natural devastation, but in broader perspective a wildfire wields a much larger force. According to David Bowman, a professor of forest ecology at the University of Tasmania in Hobart, Australia, “Fire is a feature of our planet. High levels of fire activity have the capacity to change climate”.
As wildfires are getting larger and stronger across the globe with an increasing incidence of mega-fires, scientists are now calling for an inclusion of “fires” in the next Intergovernmental Panel on Climate Change models. For such large-scale wildfires can also pose a risk of upsetting new carbon trading schemes because of their capacity to release huge amounts of carbon dioxide into the atmosphere. The ATMOSPHERIC EFFECTS of wildfires are finally being taken seriously.
The landmark report published in SCIENCE on April 24th, 2009, is the concerted effort of 22 scientists from a range of disciplines and countries to better understand the global impact of wildfires. It examines how wildfires are contributing to the overall global warming trend much more than imagined and thereby exacerbating conditions for a greater incidence of wildfires in the years to come.
EFFECTS OF WILDFIRES
Wildfires have always posed a threat. In recent years, studies have revealed that the effects of wildfires are increasingly having long-term ramifications. These secondary effects of wildfires affect both the biome and the environment. Amongst them, the more widespread and long-term effects of wildfires are the atmospheric effects, which may not be as readily visible, but are nevertheless, catastrophic.
As air gets heated and rises, large wildfires can create powerful updrafts that draw air from surrounding areas. Great vertical differences in temperature and humidity can also cause immediate extreme weather conditions. These are not just formation of pro-cumulonimbus clouds, but also intense winds exceeding even 50 miles and hour and extreme fire conditions of prolific crowning or spotting, fire swirls, rapid and wide spreads.
ATMOSPHERIC EFFECTS OF WILDFIRES
Wildfires are influencing the global ecosystem patterns, like vegetation distribution, the carbon cycle and climate. They can have a huge impact on the amount of greenhouse gases, particularly carbon dioxide, in the atmosphere. For instance, scientists found that fires in Indonesia during 1997 spewed the same amount of carbon into the air, as is typically removed annually by the entire planet’s biosphere.
EFFECTS ON CLIMATE AND WEATHER PATTERNS
The consequent localised warming from wildfires and CO2 emissions into the atmosphere, obviously contribute to the ongoing global warming scenario. At the same time, there occur short-term effects in weather patterns. There may also occur shifts in climate change and precipitation patterns in the aftermath of widespread wildfires, with some areas facing droughts or sometimes even irregular and unpredictable rainfall.
Wildfires and their atmospheric effects form 8 out of the total 29 identified climate forcing agents. Thus, wildfires and their emissions contribute to climate change, by virtue of their contributions to the atmosphere.
A domino effect of wildfires on the atmosphere is from the inhibiting and burn-up of vegetation growth, which affects the overall carbon sink of forest cover. For instance in peat fires, a variation of wildfire, the storehouse of terrestrial carbons, the peat bogs are burnt up.
EFFECTS ON OVERALL GLOBAL POLLUTION
Where smoke plumes from wildfires can be traced intact for distances even exceeding 1000 miles, it becomes a forgone conclusion that wildfires contribute to atmospheric pollution. Using atmospheric dispersion modelling, the pattern and type of pollution can be gauged to give a broader picture of the effects of wildfires.
Wildfire atmospheric emissions contain greenhouse gases like carbon dioxide, methane, nitrous oxides, ozone and CFCs and several criteria pollutants that additionally include carbon mono oxide, volatile organic compounds.
Sometimes the prevalent weather in the wildfire area, may also produce an irreversible atmospheric effect. The fire-induced convective cloud called pyrocumulonimbus is a vertically develop cloud formed above the wildfire zone, from the thermal heat or from buoyancy of wildfire plume emissions. Formation of these pyrocumulonimbus clouds may cause light precipitation, hail or even tornadoes, together with lightning and extreme low-level windy conditions. Excess of these pyro-cb clouds may also cause huge amounts of smoke to be injected in the lower stratosphere. Thus pollutants like soot and other particulate matter also reaches the lower stratosphere, which is the zone for intense and rapid interactions among radiative, dynamical and chemical processes. These have long term and far reaching consequences on the overall global climate.
EFFECTS ON ATMOSPHERIC CHEMISTRY
The increasing incidence of wildfires have the potential to irreversibly affect the atmospheric chemistry, by changing the global carbon balance, which is of serious concern today. Release of carbon and simultaneous destruction of terrestrial carbon-keepers, the vegetation cover, invariably affects the carbon levels in the atmosphere.
A study of 2.5-million-hectare sample region of Borneo affected by wildfires, revealed that 32 percent of the overall area had burned and that most of the land affected was comprised of peat bogs, which was actually effective at storing terrestrial carbon. Thus the fire’s pattern had a significant effect on the global carbon budget. (September 27, 1997) “By extrapolating their findings to the country as a whole, the scientists determined that between 0.8 billion and 2.6 billion tons of carbon was released into the atmosphere by the fires, is equivalent to 13 to 40 percent of the annual emissions from burning fossil fuels, making wildfires significant contributors to the largest jump in atmospheric carbon dioxide levels since record-keeping began in 1957”.
EFFECTS ON OVERALL GLOBAL WARMING
As vegetation burns, it also releases stored-up carbon into the atmosphere, thus speeding up global warming. Also atmospheric models indicate that the concentrations of sooty particles from wildfires could also increase absorption of incoming solar radiation during winter months by as much as 15%, further accelerating the global warming process.
