The study, lead by geography professor Mitchell Power, found that the extent and intensity of wildfires on a continental and global basis is connected to changing temperatures and climate. The study dismissed the theory that population decline was the primary cause for reduced wildfire during the cooler periods in the last 2000 years arguing "climate change was likely more important than indigenous population collapse in driving this decline."
Drought and high temperatures continue to soar across the central plains and midwest of the United States creating the hottest July on record and the hottest month ever recorded according to NOAA.
The high temperatures and extensive drought conditions have brought ideal fire weather, with wildfires that burnt over two million acres across the United States just in July, ranked fourth in acres burnt since 2000. The record area burnt was 3.4 million acres in 2004.
"The drop in fire [after about A.D. 1500] has been linked previously to the population collapse. We’re saying no, there is enough independent evidence that the drop in fire was caused by cooling climate," said the study’s principal author, Mitchell Power, an assistant professor of geography at the University of Utah.
"The implication is that climate is a large-scale driver of fire. That’s a key finding. Climate is driving fire on global and continental scales," said Power.
The study analyzed charcoal samples spanning the last 2000 years and covered the period of the Little Ice Age which started from somewhere between 1200 and 1500 and ended in the early 1800s. The samples were collected from 600 sites around the world, about half in the Americas.
"The decrease in fire on a very large scale – globally and in the Americas – was controlled by this cooling climate, which began prior to the population collapse, and climate alone is sufficient to explain large scale changes in burning," says Power.
According to the study the decline of wildfires was not limited to heavily populated areas, but stretched from the boreal forests of northern Canada to the Patagonian tip of South America.
With the drought conditions continuing across much of the plains and midwest United States the relationship between a warming climate and extreme fireweather should be a serious concern. "In a world where climate is rapidly changing we need to pay more attention to this relationship between climate and fire," Power said.
Here is how NOAA describes the conditions in the State of the Climate Wildfires report for July 2012 for the United States:
The warm and dry weater created ideal wildfire conditions across a large portion of the country. According to the U.S. Drought Monitor, the percent area of the contiguous U.S. experiencing Moderate-to-Exceptional Drought (D1-D4) grew from 56.0 percent on July 3rd to 62.9 percent on July 31st. Drought improved across the Northeast and along the Gulf Coast, while the rest of the nation experienced continuing or worsening drought conditions. Drought conditions worsened by one to two categories across the Midwest, the Plains, the mid-South, and parts of the Intermountain West. The percent area of the contiguous U.S. experiencing Extreme-to-Exceptional Drought (D3-D4) doubled in size during July, from 10.3 percent on July 3rd to 22.3 percent on July 31st.
The month of July started with some 57 wildfires active across the United States. By mid July this had reduced to 32 wildfires across the western states. By July 31st there were 29 large wildfires, 20 of which were in the western states, two in Florida and several across southern plains and the mid-south.
The study lead by Mitchell Power should be a wake up call to reduce carbon emissions to slow global warming to forestall more extreme fire weather conditions. Fire conditions that also impact human health and agriculture.
"In a cooler atmosphere, you tend to get reduced convection, so you get reduced thunderstorms and ignition from lightning," said Mitchell Power, "Cooler climate also tends to maintain high levels of fuel moisture and soil moisture."
You can read more from the University of Utah Media Release: When the World Burned Less (Study: Cool Climate, Not Population Loss, Led to Fewer Fires)
Mitchell Power lead an international team of 19 scientists and published the study online - Climatic control of the biomass-burning decline in the Americas after AD 1500 (abstract) - at The Holocene journal on 14 August 2012. ( doi: 10.1177/0959683612450196 )
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