A wildfire is any uncontrolled, non-structure fire that occurs in the wildland. Synonyms such as wildland fire, forest fire, brush fire, vegetation fire, grass fire, peat fire, bushfire (in Australasia), and hill fire are commonly used. Causes are numerous and include lightning, human carelessness, slash-and-burn farming, arson, volcanic activity, pyroclastic clouds, and underground coal fires. Nine out of ten wildfires are reportedly caused by some human interaction. Heat waves, droughts, and cyclical climate changes such as El Niño can also dramatically increase the risk of wildfires.
Wildfires are common in various parts of the world, ocurring in cycles. They are often considered beneficial to wildlands, as many plant species are depend on the effects of fire for growth and reproduction. However, large wildfires often have detrimental atmospheric consequences.
Wildfires are common in climates that are sufficiently moist to allow the growth of trees but feature extended dry, hot periods. Such places include the vegetated areas of Australia, the veld in the interior and the fynbos in the Western Cape of South Africa, and the forested areas of the United States and Canada. Fires can be particularly intense during days of strong winds and periods of drought. Fire prevalance is also high during the summer and autumn months, when fallen branches, leaves, grasses, and scrub dry out and become more flammable. Global warming may increase the intensity and frequency of droughts in many areas, creating more intense and frequent wildfires. Forest fires can have a dramatic effect on climate change, dramatically increasing carbon released into the atmosphere and ceasing vegetation growth, which inhibits carbon uptake.
Wildfires can affect climate and weather and have major impacts on regional and global pollution. Wildland fire emissions contain greenhouse gases and a number of criteria pollutants which can have a substantial impact on human health and welfare. Forest fires in Indonesia in 1997 were estimated to have released between 0.81 and 2.57 gigatonnes of CO2 into the atmosphere, which is between 13-40% of the annual carbon dioxide emissions from burning fossil fuels. Atmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming solar radiation during winter months by as much as 15%.
The IPCC Fourth Assessment Report predicts that many mid-latitude regions, such as Mediterranean Europe, will experience decreased rainfall and an increased risk of drought, which in turn would allow forest fires to occur on larger scale, and more regularly. This releases more stored carbon into the atmosphere than the carbon cycle can naturally re-absorb, as well as reducing the overall forest area on the planet, creating a positive feedback loop. Part of that feedback loop is more rapid growth of replacement forests and a northward migration of forests as northern latitudes become more suitable climates for sustaining forests. There is a question of whether the burning of renewable fuels such as forests should be counted as contributing to global warming.
Pine forests in British Columbia have been devastated by a pine beetle infestation, which has expanded unhindered since 1998 at least in part due to the lack of severe winters since that time; a few days of extreme cold kill most mountain pine beetles and have kept outbreaks in the past naturally contained. The infestation, which (by November 2008) has killed about half of the province's lodgepole pines (33 million acres or 135,000 km2) is an order of magnitude larger than any previously recorded outbreak and passed via unusually strong winds in 2007 over the continental divide to Alberta. An epidemic also started, be it at a lower rate, in 1999 in Colorado, Wyoming, and Montana. The United States forest service predicts that between 2011 and 2013 "virtually all 5 million acres of Colorado’s lodgepole pine trees over five inches in diameter will be lost"
As the northern forests are a carbon sink, while dead forests are a major carbon source, the loss of such large areas of forest has a positive feedback on global warming. In the worst years, the carbon emission due to beetle infestation of forests in British Columbia alone approaches that of an average year of forest fires in all of Canada or five years worth of emissions from that country's transportation sources
Besides the immediate ecological and economic impact, the huge dead forests provide a fire risk. Even many healthy forests appear to face an increased risk of forest fires because of warming climates. The 10-year average of boreal forest burned in North America, after several decades of around 10,000 km² (2.5 million acres), has increased steadily since 1970 to more than 28,000 km² (7 million acres) annually. Though this change may be due in part to changes in forest management practices, in the western U. S., since 1986, longer, warmer summers have resulted in a fourfold increase of major wildfires and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity has been reported in Canada from 1920 to 1999.
For More Information:
Effects of Global Warming
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