(From Environmental Research Web http://environmentalresearchweb.org/cws/article/news/69499)

Fire-induced changes to ecosystems have a greater impact on the climate than land-use and land-cover change, according to researchers in China and the US.

The study is the first to quantify the global impact of fire by its effect on ecosystems, rather than by its emission of trace gases and aerosols. Fire-induced changes to ecosystems boosted surface air temperatures by 0.18°C above the 20th century average, the researchers found.

"Our work is critical to improve our understanding of fire’s role in the Earth system as well as the potential broader impact of fire management, and to provide a direct reason supporting why Earth system models should include fire modelling for global research agendas," said Fang Li of the Institute of Atmospheric Physics at the Chinese Academy of Sciences in Beijing.

Fire exerts huge impacts on terrestrial ecosystems. When fire passes through a region, it can damage tree roots, many or most of the stems, and almost all leaves and grasses.

To date, most studies of how fire affects the climate have focussed on the emission of trace gases and aerosols. To explore the effects on the climate through changes in ecosystems has been more difficult, says Li, because there are many more interacting factors.

Together with David Lawrence at the US National Center for Atmospheric Research and Ben Bond-Lamberty at the Pacific Northwest National Laboratory, also in the US, Li performed simulations with the Community Earth System Model, which represents the atmosphere, land surface, carbon cycle and other key subsystems. The researchers ran the simulations with and without fires, to quantify the overall impact of fire-induced changes to ecosystems.

The impacts were greater than they had anticipated, particularly for tropical savannah. Fire-induced changes boosted surface air temperatures primarily by reducing the latent heat flux – when water evaporates from the land surface, taking heat with it. In addition, fire-induced changes cut surface net radiation – the radiation absorbed by the Earth’s surface – mainly because fire-induced surface warming boosts the amount of longwave radiation emitted from the land.

The study complements previous fire studies that have described mostly a cooling effect, because of reductions in shortwave radiation. "Fire-induced changes within ecosystems lead to significant warming, mainly by reducing latent heat flux," said Li. "The magnitude of this latter effect has not been understood before now, leading to a misunderstanding of fire’s global impact on the climate, and related mechanisms."

The researchers are now planning to understand the effect of all fire impacts taken together. They will use a new version of the Community Earth System Model set to be released in August.

The team published the study in Environmental Research Letters (ERL).

Contact: LI Fang, lifang@mail.iap.ac.cn