For the last 2,000 years the climate has been the major cause of wildfires, but during the late 19th and early 20th century, human activity dramatically reduced burning in many parts of the world, according to new research published in
Nature Geoscience this week.
The study by two scientists from the University of Bristol, with colleagues in Europe and North America, was based on analysis of records from more than 400 ancient charcoal sites taken from lakes on six different continents.
Up to about 1750 the records show there is a gradual decrease in wildfires worldwide, probably resulting from a long-term global cooling trend that culminated in the Little Ice Age. This cooling offset any possible influence of population growth and related land-use changes on fire.
After 1750, the charcoal record shows an increase in wildfires coincident with rising atmospheric carbon dioxide and population growth. The highest levels of fire activity in the last 2,000 years occurred between 1750 and 1870. Several factors such as land clearance, the introduction of intensive grazing and fire management combined to generate conditions favourable to wildfire at this time.
Professor Sandy Harrison from the University of Bristol said: “The 100-year decline in wildfires worldwide recorded between 1870 and 1970 is contemporaneous with an unprecedentedly high rate of population increase. This led us to conclude the decline reflects a global expansion of agriculture and intensive grazing of livestock, which in turn reduced the amount of fuel available for wildfires. Improved fire-management may also have played a role.”
However, the researchers cautioned that the sediment record does not provide information on trends in the last 30 years – when observations suggest increased burning is associated with global warming and fuel build-up.
Charcoal records have drawn increasing attention from researchers during the past 25 years because these data can track wildfire activity – both incidence and severity – over very long time periods, beyond the timescale for which we can use observations of fires from satellites or from fire-scarred trees.
Reference: Climate and human influences on global biomass burning over the past two millennia. J. R. Marlon, P. J. Bartlein, C. Carcaillet, D. G. Gavin, S. P. Harrison, P. E. Higuera, F. Joos, M. J. Power & I. C. Prentice. Nature Geoscience, published online: 21 September 2008 | doi:10.1038/ngeo313.
Provided by University of Bristol
Related stories:
Climate change, human activity and wildfires
Climate has been implicated by a new study as a major driver of wildfires in the last 2,000 years. But human activities, such as land clearance and fire suppression during the industrial era (since 1750) have created large swings in burning, first increasing fires until the late 1800s, and then dramatically reducing burning in the 20th century.
When it comes to forest soil, wildfires pack 1-2 punch
For decades, scientists and resource managers have known that wildfires affect forest soils, evidenced, in part, by the erosion that often occurs after a fire kills vegetation and disrupts soil structure. But, the lack of detailed knowledge of forest soils before they are burned by wildfire has hampered efforts to understand fire's effects on soil fertility and forest ecology.
Wildfires cause ozone pollution to violate health standards, new study shows
Wildfires can boost ozone pollution to levels that violate U.S. health standards, a new study concludes. The research, by scientists at the National Center for Atmospheric Research (NCAR), focused on California wildfires in 2007, finding that they repeatedly caused ground-level ozone to spike to unhealthy levels across a broad area, including much of rural California as well as neighboring Nevada.
High mountain meadows are disappearing as trees move higher
Nothing lures visitors to Paradise like the transitory displays of wildflowers that populate Mount Rainier's high mountain meadows.
Scientists point to forests for carbon storage solutions
Scientists who have determined how much carbon is stored annually in upper Midwest forests hope their findings will be used to accelerate global discussion about the strategy of managing forests to offset greenhouse gas emissions.
Thawing permafrost likely to boost global warming
The thawing of permafrost in northern latitudes, which greatly increases microbial decomposition of carbon compounds in soil, will dominate other effects of warming in the region and could become a major force promoting the release of carbon dioxide and thus further warming, according to a new assessment in the September 2008 issue of
BioScience.
New Report: Greatest Value of Forests is Sustainable Water Supply
(PhysOrg.com) -- The forests of the future may need to be managed as much for a sustainable supply of clean water as any other goal, researchers say in a new federal report – but even so, forest resources will offer no “quick fix” to the insatiable, often conflicting demands for this precious resource.
Study: Future snowmelt in West twice as early as expected; threatens ecosystems and water reserves
According to a new study, global warming could lead to larger changes in snowmelt in the western United States than was previously thought, possibly increasing wildfire risk and creating new water management challenges for agriculture, ecosystems and urban populations.
