Dark brown carbon from biomass burning contributes to significant global-scale positive forcing

Light-absorbing organic aerosol, known as brown carbon (BrC), is a warming agent affecting global climate. Recent evidence reveals that wildfires and agricultural burning emit a distinct class of material, dark BrC (d-BrC), with significant visible and near-infrared absorption not yet evaluated in climate models. Here, we present a global model simulation showing that d-BrC contributes a substantial radiative effect of +0.208 Wm-2 (+0.02 to 0.68 Wm-2) via its solar radiation absorption, comparable to black carbon and far exceeding traditional BrC estimates. Comparisons against aircraft measurements suggest that inclusion of d-BrC resolves some discrepancies between simulated and observed aerosol absorption unexplained by uncertainties in other aerosols. Our findings identify d-BrC as a critical climate forcer and highlight the importance of incorporating d-BrC into models to accurately assess climate impacts of aerosols and fires.