Global fire records for last 2000 years show striking human influence
29 September 2008
Close links between wildfires and climate, which dominated for 1800 years, were broken at the start of the industrial revolution. But wildfires are on the rise again.
Global wildfires fell in the last 2000 years as the climate cooled.
Climate has driven wildfires for most of the last 2000 years, according to scientists analysing the charcoal remnants in 406 sedimentary cores from six continents. But in the last 200 years, people have exerted a stronger influence.
The most detailed compilation - or synthesis - of fire records yet shows that wildfires decreased from 1 AD for 1800 years in line with long term global cooling. Blazes slumped to a minimum during the Little Ice Age, around 1550 to 1750, before rising steeply at the start of the industrial revolution following rapid population growth.
But the international team of scientists did not expect what happened next. Globally, fires peaked from 1870 to 1890, then, bucking the trend, they nose-dived hitting a new low in the 1970s. Sedimentary cores don't record what has happened since then, though other evidence points to a global shift back to more fires.
Global fire trends over the last 2000 years.
Professor Sandy Harrison from the University of Bristol explains, 'I think over the nineteenth and twentieth centuries, the warmer climate drove more fires.'
'Warmer climates will naturally cause more fires. We are entering a new fire regime.'
Professor Sandy Harrison
But large-scale grazing quickly left less and less fuel for fire. This was compounded by fragmentation of the landscape which artificially curbed fires that would have once burned out of control. Land fragmentation and grazing may have peaked in the 1950s.
'Warmer climates will naturally cause more fires. It looks like this is overcoming human suppression. We are entering a new fire regime,' adds Harrison.
'If, as our work has shown, people were inhibiting climate-induced fires until recently, then the increase in fires in the next decade may be spectacular.'
Harrison says that the fires raging through southern Europe over the last few years may be the first evidence of what is to come.
The global fire synthesis, published in the journal Nature Geoscience (doi:10.1038/ngeo313), , has a bias towards North and South America and Europe. Fire records from Africa and Russia are sparse but the QUEST (Quantifying and Understanding the Earth System) team are adding around another 200 sites later this year. They hope this will create a more comprehensive picture and ensure their figures add up.
The work, a far-reaching initiative on fire from the NERC-funded QUEST programme, is part of the International Geosphere-Biosphere programme. The international team involved in the Nature Geoscience paper were funded by the Natural Environment Research Council in the UK and the National Science Foundation in the United States. The lead author was Jennifer Marlon from the University of Oregon.
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