Increase in global warming potential of atmospheric black carbon since 1750

Black carbon is a short-lived climate forcer that occurs as a continuum of particulate matter with varying physical, chemical and optical properties. However, current global climate assessments treat black carbon as a single compound, overlooking the distinct properties of its subtypes and introducing substantial uncertainty in determining its climate impact. Here we evaluate the climate relevance of this overlooked heterogeneity using approximately 2,500 thermal–optical measurements of carbon fractions across emission sources to develop a global inventory distinguishing between less light-absorbing char and more light-absorbing soot from 1750 to 2019. We observed an increase in the soot fraction of total anthropogenic black carbon emissions, from 16% in 1750 to 35% in 2019, primarily driven by increased fossil fuel consumption. This shift, aligning with sediment records, suggests that contemporary black carbon emissions possess greater global warming potential per unit mass than those at the onset of the industrial era. Our findings underscore the need to resolve black carbon subtypes in climate models and prioritize soot-rich sources for mitigation.