Study weakens link between global warming, wildfires

By Ryan Shelton, Asst. News Editor

As the global debate over climate change intensifies, a new study involving U researcher Mitchell Power found the number of wildfires worldwide decreased in the 20th century, despite rising temperatures and sweeping droughts.

The two-year study found a 100-year decline in wildfires worldwide from 1870 to 1970 after analyzing 406 sedimentary charcoal records from lake beds on six continents.

Similar to studying tree rings, the lake bed soil samples allow researchers to examine each region’s climatic and biological history. Large deposits of charcoal, or burnt plant material, indicate wildfires.

The study was conducted by a nine-member team from seven institutions and was co-led by Power, who is the new curator of the Garrett Herbarium at the Utah Museum of Natural History and new associate professor in the department of geography.

Powers, who arrived at the U in early August from the University of Edinburgh in Scotland, said the panel was surprised by the decrease in wildfires, concluding that human activity, such as the expansion of agriculture, intensification of livestock grazing and effective fire management, led to the decrease.

“We all assumed that climate change in the 20th century would result in a exponential increase of wildfires worldwide,” Power said. “The only time in the last 2,000 years humans have impacted wildfires was in the last century.”

The analysis of charcoal has drawn increasing attention from researchers in the last 25 years because the data can track wildfire activity8212;both incidences and severity8212;over long periods of time, providing information for periods when similar data from satellites or fire-scarred trees do not exist.

The study, which was published in the Nature Geoscience journal Sept. 21, suggests that during the past 2,000 years, global fire activity was highest between 1750 and 1870 as a result of population growth, massive changes in land cover and human-induced increases in atmospheric carbon dioxide concentrations. However, the expansion of intensive agriculture and grazing, as well as forest management activities in the 20th century, likely reduced wildfire activity.

Power said if the Earth continues to warm at its current rate, high-elevation conifer forests in the western United States, such as the Uinta Mountains, will be at risk for increased wildfires.

Power is also putting the herbarium’s plant collection into a database and exploring the causes of changing plant distribution through time. The collection contains more than 126,000 plant specimens collected over the past 150 years. It is the second largest collection in Utah and ranks in the top 15 percent worldwide.

“It’s really going to be a great resource for the local and scientific community,” Power said. “People who want to know what’s growing in their backyards can bring in a plant, and we’ll figure out what they’ve got.”

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