What are the carbon costs of wildfires?

Wildfires can be highly destructive events which burn through various ecosystems, threaten people and infrastructure, and release carbon dioxide into the atmosphere. However, according to a new study led by the University of Zurich, many wildfires are part of a natural regime of disturbance and post-fire recovery with a neutral impact on carbon storage over long timescales. The findings suggest that, in the long term, more carbon could end up being stored rather than released in savannahs and grasslands, which are the areas most affected by wildfires.

The researchers aimed to construct the most complete budget to date of the impact of wildfires on the carbon cycle, accounting for both short-term and long-term effects of wildfires on land carbon storage. By using a land surface model, they assessed the global impact of fires on the amount of carbon stored in soils and vegetation between 1901 and 2010.

“This study is about improving how we understand the process of fire on a range of timescales,” said study co-author Dr. Matthew Jones, an expert in the relationship between climate and wildfires at the University of East Anglia. “In essence, fires are unquestionably a source of carbon in the short-term, but these short-term effects could be counteracted by sinks of carbon in the long-term.”

According to Dr. Jones and his colleagues, these wildfire-related carbon sinks account to approximately 90 million tons of carbon dioxide being sequestered by soils and vegetation annually. However, the scientists could not yet reliably model the rate at which carbon is released back to the atmosphere as charcoal breaks down in soils.

“The missing piece in the puzzle is a conclusive understanding of how quickly charcoal breaks down in soils. We couldn’t model the timescale of this process due the poor availability of measurements, and hence the process is not included in our latest budget,” said Dr. Jones.

Regardless of this shortcoming, the findings strongly suggest that wildfires have a milder impact on the climate as previously estimated. “What is clear is that fires are very likely to be close to neutral, meaning that the average lifespan of charcoal in soils is around 5,000 years – well over a hundred times that of your average soil carbon,” explained study lead author Dr. Simon Bowring, a postdoctoral researcher at the University of Zurich.

“We urgently need increased efforts towards understanding the mechanisms underlying its movement to the atmosphere. As important, and independent of the previous consideration, the positioning of wild grasslands in the climate perspective likely requires substantial reassessment,” he concluded.   

The study is published in the journal Nature Geoscience.

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By Andrei Ionescu, Earth.com Staff Writer