Brown carbon from biomass burning imposes strong circum-Arctic warming

Rapid warming in the Arctic has a huge impact on the global environment. Atmospheric brown carbon (BrC) is one of the least understood and uncertain warming agents due to a scarcity of observations. Here, we performed direct observations of atmospheric BrC and quantified its light-absorbing properties during a 2-month circum-Arctic cruise in summer of 2017. Through observation-constrained modeling, we show that BrC, mainly originated from biomass burning in the mid- to high latitudes of the Northern Hemisphere (∼60%), can be a strong warming agent in the Arctic region, especially in the summer, with an average radiative forcing of ∼90 mW m−2 (∼30% relative to black carbon). As climate change is projected to increase the frequency, intensity, and spread of wildfires, we expect BrC to play an increasing role in Arctic warming in the future. [Display omitted] •Brown carbon imposes strong Arctic warming•Warming effect of water-soluble brown carbon is ∼30% relative to black carbon•Biomass burning contributes ∼60% of the warming effect of brown carbon•Warming climate leads to increased wildfires that reinforce Arctic warming Rapid Arctic warming and associated glacier and sea ice melt have a great impact on the global environment, with implications for global temperature rise and weather patterns, shipping routes, local biodiversity, and methane release. Greenhouse gases and black carbon aerosols are well-known warming agents that accumulate in the Arctic atmosphere, but full warming agent picture remains incomplete, preventing accurate forecasts. The effects of brown carbon—an aerosol derived from biomass and fossil fuel burning—are particularly unclear. Through observations from a circum-Arctic cruise and numerical model simulations, we show that light-absorbing brown carbon, mainly from biomass burning, can impose a strong warming effect in the Arctic, especially in the summertime. If, as predicted, the frequency, intensity, and spread of wildfires continues to increase, this may reinforce circum-Arctic warming and further contribute to global warming, forming a positive feedback. In light of these results, the careful management of vegetation fires, especially in the mid- to high latitudes of the Northern Hemisphere, will prove important in mitigating the warming in the Arctic region. The Arctic is warming at an excessive rate of more than three times as fast as the rest of the globe, exerting strong impacts on the Earth’s climate, as well as on ecosystems a