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

Biomass burning from forest fires, agricultural burning, and other fires releases particles that can absorb sunlight and contribute to climate warming. For years, attention has focused on the “black carbon” (BC) component of these particles, which is considered to have high warming potential. However, more recently, attention has shifted to include brown carbon (BrC) materials, which are less well understood. BrC has been viewed as not very efficient at absorbing visible light and susceptible to photobleaching, thus translating into a relatively small warming effect compared to BC. However, more recent evidence shows that there is a specific type of BrC, dark BrC (d-BrC) that is water insoluble and can absorb sunlight throughout the visible and near-infrared spectrum, complicating its warming potential and, thus, our ability to accurately predict climate effects. Here, a computational model is used to simulate the contribution of d-BrC to solar absorption, and it shows that d-BrC is actually able to cause a substantial amount of atmospheric warming comparable to BC. Including this new insight in models resolves some discrepancies with atmospheric measurements that have not been explained by other factors. Accounting for d-BrC’s effects will improve climate assessments and help inform mitigation policies targeting emissions from fires.