Forest Fires Mostly Overlooked by Climate Modelers (Update1)

April 24 (Bloomberg) -- Forest fires worsen global warming and make it harder for societies to adapt to drought and higher temperatures, scientists said.

Trees and brush set ablaze, by accident or through slash- and-burn farming in the tropics, fuel hotter weather, said Jennifer Balch, a researcher at the National Center for Ecological Analysis and Synthesis in Santa Barbara, California. That’s because smoke adds more carbon dioxide to the atmosphere.

“We don’t think about fire correctly,” Balch said. “It’s very intrinsic to the planet.”

The emissions of carbon dioxide, a greenhouse gas adding to global warming, are about equal to half the output from burning fossil fuels such as coal, Balch and colleagues wrote in a study published yesterday in the journal Science on the role of fire in the climate system.

Even so, the effect of fires doesn’t figure often enough in models that predict future global warming. New events and findings should be incorporated more quickly in climate models rather than take several years, experts say.

“The present modeling is based on a range of assumptions” that don’t always take into account “big events” quickly enough, like the 2005 Amazon rain forest drought that helped spark fires, said Kim Carstensen, climate-change program director for the environmental group WWF International.

‘Credible, Trustworthy’ Climate Policy

“The argument on the other side is we need to be sure science is not just based on one study,” Carstensen said today in a telephone interview from Copenhagen. “We really, really need climate policy to be credible and trustworthy.”

Scientists are still looking for ways to properly quantify the influence of fires on the earth’s climate system, Balch said in an interview.

Almost one-third of the planet experiences frequent fires, according to research by Emilio Chuvieco, a geographer at the University of Alcala, Spain, and colleagues. The frequency of fires is increasing as regions such as western North America become warmer and drier, said Balch.

Forecasting models haven’t incorporated the link between fire and global warming enough to date, Thomas Swetnam, director of the University of Arizona’s Laboratory of Tree-Ring Research, was quoted as telling the Arizona Daily Star newspaper.

“The biggest concern I have is that it is possible that we are underestimating the positive feedback of fire to the climate system and affecting future climate,” Swetnam, a co-author on the study, told the newspaper. “We may be underestimating how much carbon future fires will contribute to the atmosphere.”

‘Huge Task to Accomplish’

It’s a “huge task to accomplish to integrate dynamic vegetation models into the climate models, and it needs more time and careful work,” said Kirsten Thonicke, a researcher in geoecology at the Potsdam Institute for Climate Impact Research in Germany.

“If you want to do projections 50 or 100 years from now or even further, you want to know if your biosphere is still able to provide you with the fuel you need to burn,” Thonicke said.

It’s clear that fires occur systematically when there is wood to burn, lightning strikes or humans set blazes amid hot and dry climate conditions, Balch said.

Fires in Southeast Asia in 1997 and 1998 related to the El Nino effect cost the region’s economy about $9 billion, including $1 billion in health-related expenses because of smoke inhalation. As much as $15 billion in damage resulted from fires in South America the same year.

Old-Growth Forests

Old-growth forests once studded with pine and firs from California to British Columbia are being consumed more regularly by fire as temperatures have risen as much as 0.5 degrees Celsius (0.9 degrees Fahrenheit) a decade since the 1970s, U.S. Geological Survey researcher Phillip van Mantgem said.

The earth in general is a flammable planet with carbon-rich vegetation, periodic dry seasons, lightning and volcanic eruptions, Balch and colleagues wrote in the study. Even wet forests like the Amazon can become combustible if invasive species take hold or as a result of human-induced burning.

Increased frequency of fires also will have an impact on carbon markets if negotiators at United Nations climate talks include forest preservation in a new climate-protection treaty, Balch said.

While present climate models don’t include specific inputs to take account of forest fires, they do include the dying off of vegetation, which can result from fires, said Olivier Boucher, head of chemistry and ecosystems at the U.K. Met Office, the government forecaster.

“Including forest fires won’t change predictions of climate change by a large percentage,” Boucher said today from Exeter, England. Even so, “we want models which are increasingly realistic and fires are missing.”

To contact the reporter on this story: Jeremy van Loon in Berlin at jvanloon@bloomberg.net.

To contact the editor responsible for this story: Todd White at twhite2@bloomberg.net.