A recent University study shows humans have been significantly influencing wildfire behavior during the last 250 years, but University doctoral student Jennifer Marlon and geography professor Patrick Bartlein expect this relationship between humans and fire is about to change.
The study, led by Marlon, helped create a database of worldwide fire activity spanning the last 2,000 years. More than 80 scientists from across the globe have added their own statistics to the trove of information gathered from Marlon’s study.
The study found climate patterns influence wildfire activity more often and over longer periods of time than human activity. As Earth’s climate continues to warm, fire frequency around the world is expected to increase.
Bartlein, who worked with Marlon on the study, pointed out that until the beginning of the industrial revolution around 1750, fire activity was decreasing because of global cooling.
However as soon as the industrial revolution began fires increased rapidly, especially in areas settled by Europeans who needed to clear room for cities and farming by burning.
Once settling was complete, around 1870, humans made common the practice of extinguishing fires and caused a sharp decline in fire activity. The decline has continued until the present day.
Putting fires out wasn’t the only way humans reduced the number and frequency of fires. Cropland, pastures, infrastructure, and urbanization all reduced forests, grasslands and natural brush wildfires would have previously been burning.
Years of humans putting fires out has built up vegetation, especially in forested and wilderness areas, Bartlein explained. This means fires are going to get bigger because there is more for them to burn.
And in areas where human intervention has been minimal, such as Siberia and Northern Europe, warmer climates are already increasing fire behavior. Global warming patterns are expected to overtake human effects in other parts of the globe soon, counteracting the decline in fires that has been the recent trend.
“Studies of fires in the last couple of decades have shown that fires are getting larger, and the fire season is getting longer, so it appears that the close relationship between temperatures and fire is resuming now,” Marlon said in an e-mail.
The increase in fire activity as global warming continues is going to be significant.
In an e-mail, Marlon explained fires affect the global climate by burning vegetation and by producing carbon emissions, among other things. Therefore, models that simulate global climate need to take changes in fire activity into account.
When a fire burns, it emits carbon into the air, which eventually lands and gets washed down watersheds, finally settling in the bottoms of lakes and peat bogs.
In those lakes and bogs Marlon, Bartlein and their team took samples of sediments, located the carbon, measured it and dated it. Higher levels of carbon in a date range meant more fires during that time.
Marlon hopes by putting all the data in one place and in one format, researchers from many different disciplines will be able to contribute to and draw from the information to improve their understanding of fire on long-term scales.
Bartlein added, “When you look at the past 2,000 years, you can’t point to just one factor. The big question is what’s going to happen in the future as climate changes.”
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