Citizen Staff Writer
ALAN FISCHER
afischer@tucsoncitizen.com
Man-caused fires play a significant role in global climate change, a University of Arizona researcher said Thursday.
“We found that approximately 20 percent of the warming effect of greenhouse gases is coming from deforestation fires set by people,” said Thomas W. Swetnam, UA professor and director of the Laboratory of Tree-Ring Research.
“This is more precise than what was previously available,” he said.
That figure includes only deforestation fires, or ones deliberately set to convert forests – often tropical rain forests – into farmlands and pasturelands, he said.
It does not include the wildfires – caused by man or acts of nature – that are seen regularly in the western United States and other areas, Swetnam said.
Large fires have a “feedback effect” that leads to more fires as well as climate change, Swetnam said.
“Warming conditions lead to more droughts, which lead to more fires. The fires release emissions, those go into the atmosphere and increases warming further,” he said. “Fire can actually generate more fire.”
This can include forest fires.
There are increasing numbers of so-called megafires in the western United States, Canada, Siberia and other regions, Swetnam said.
These megafires are at least partially driven by regional and global warming trends, he said.
“In the western United States, we have seen more than a sixfold increase in the total area burned the past two decades compared to the previous two decades,” he said. “Fire season in the western United States has increased by more than two months.”
Deadly fires in Australia are another example of the trend.
“Because of the high levels of industrial pollution that is changing the climate, we are already seeing changes in fire activity on Earth,” said David Bowman of the University of Tasmania in Hobart, Australia.
Bowman is a co-author of the paper that appears Friday in Science.
While the study more accurately reflects fire’s impact on climate change, much work remains, Swetnam said.
“In this paper, we make pains to talk about the difficulties and uncertainties that remain,” he said. “This is still a coarse-scale estimate on how much burning by people is contributing to global warming.
“It could be greater. There is potential for it to be considerably larger.”
The paper, “Fire in the Earth System,” calls for more research on the role fire plays in putting greenhouse gases into the atmosphere, Swetnam said.
“If we want to understand climate change in the future, we need to build fire into the models,” Swetnam said.
“Fire is affecting people and people are affecting fire . . . we need to put fire on the center stage of our understanding,” he said.