A new international study published in Nature Geoscience reveals that dark brown carbon from wildfires exerts a powerful warming effect on the global climate—potentially matching or even exceeding that of black carbon in the visible spectrum.
Conventional understanding has held that brown carbon—a type of organic aerosol from biomass burning—mainly absorbs sunlight in the near-ultraviolet range, giving it only a limited climate impact. However, growing observations show that some wildfire-derived brown carbon appears dark brown or nearly black, absorbing light well into the visible spectrum. This “dark brown carbon” has been largely missing from global climate assessments.
Led by researchers from the Institute of Atmospheric Physics at the Chinese Academy of Sciences, Xiamen University, and Texas A&M University, the team combined aircraft, ground-based, and satellite data to analyze wildfire plumes across North America, South America, Siberia, Africa, and Australia. Their study found that at a wavelength of 500 nm (near the peak of solar radiation energy), the mass absorption efficiency of organic carbon in wildfire plumes ranges from 0.5 to 1.5 m²/g—far exceeding the typical value of less than 0.1 m²/g for weakly absorbing brown carbon. In the visible spectrum, dark brown carbon can match or surpass the light absorption of black carbon, challenging the long-held view that brown carbon absorbs much less light.
By incorporating observation-constrained optical parameters into a global climate model, the team quantified dark brown carbon’s radiative effect for the first time. The results show that wildfire-derived brown carbon has a global direct radiative effect of +0.097 W/m², with an uncertainty range of +0.050 to +0.276 W/m². Notably, the upper bound of this estimate (0.276 W/m²) exceeds the radiative contribution of black carbon (0.163 W/m²).
The study also reveals that dark brown carbon’s influence extends markedly into mid- and high-latitude regions and even the Arctic. In these snow- and ice-covered areas, deposition of dark brown carbon may reduce surface albedo and trigger a positive snow-ice albedo feedback, amplifying regional and global warming.
“This study demonstrates that dark brown carbon is a key but long-underestimated climate warming factor,” said first author Dr. Lulu Xu, a postdoctoral researcher at the Institute of Atmospheric Physics. “Against the backdrop of mutual reinforcement between global warming and increasingly frequent wildfires, future climate assessments must fully account for the warming contribution of dark brown carbon.”
Nature Geoscience
Strong global radiative effects from wildfire dark brown carbon