Black carbon, the fine particulate matter produced by incomplete combustion of fossil fuels, biomass and other carbonaceous fuels, is one of the most important short-lived climate forcers in the atmosphere. Unlike carbon dioxide, which persists for centuries, black carbon warms the atmosphere intensely but briefly, absorbing sunlight and heating the air around it. Yet global climate assessments have long treated black carbon as a single, uniform compound. The new study argues that this simplification conceals a critical truth: black carbon exists as a continuum of particles with sharply different physical, chemical and optical properties, and those differences matter enormously for climate.

To resolve this heterogeneity, an international team led by researchers at the Southern University of Science and Technology in Shenzhen, together with colleagues at the Max Planck Institute for Chemistry and other institutions, assembled approximately 2,500 thermal–optical measurements of carbon fractions across a wide range of emission sources. Thermal–optical analysis separates elemental carbon into operationally defined fractions, allowing the researchers to distinguish between two fundamentally different subtypes of black carbon: char and soot. Char is the less light-absorbing, lower-maturity form, typically produced at lower combustion temperatures, while soot is the highly graphitized, strongly light-absorbing form generated by hot, efficient combustion processes.

Using this measurement database, the team constructed a global inventory that separately tracks char and soot emissions from 1750 to 2019, spanning the full arc of industrialization. The results reveal a striking transformation. In 1750, soot accounted for only about 16 percent of total anthropogenic black carbon emissions. By 2019, that fraction had climbed to roughly 35 percent. The driver of this shift is unmistakable: the relentless growth of fossil fuel consumption. Coal combustion, diesel engines and other high-temperature fossil fuel sources produce proportionally far more soot than the smoldering biomass burning and traditional domestic fires that dominated the pre-industrial world.

The optical consequences of this compositional change are profound. Soot absorbs light far more efficiently per unit mass than char, a property quantified by the mass absorption cross section. As the soot fraction of emissions has grown, the average mass absorption cross section of anthropogenic black carbon has risen accordingly, meaning that contemporary emissions trap more solar energy per kilogram than their historical counterparts. The researchers used radiative transfer calculations, including Lorenz–Mie theory and multiple-sphere T-matrix methods, to quantify how the changing char–soot mixture alters the absorption properties of the atmospheric black carbon burden, and coupled these estimates with simulations using the Community Earth System Model version 2.1.

Crucially, the inventory’s story is not built on models alone. The shift toward a higher soot fraction aligns with independent evidence preserved in sedimentary records. Lake sediments, such as the 150-year records from Lake Phayao in northern Thailand and from lakes on the Tibetan Plateau, archive the deposition of soot and char separately, and these archives corroborate the temporal trends reconstructed from the emission inventory. The agreement between bottom-up accounting and geological archives lends considerable weight to the central conclusion: the global warming potential of atmospheric black carbon, per unit of mass emitted, has increased since the mid-eighteenth century.

The implications ripple through climate science. Because climate models and assessments such as those of the Intergovernmental Panel on Climate Change generally treat black carbon as a single compound, they may misestimate its historical and present-day radiative forcing. If today’s black carbon is more absorbing than the black carbon of 1750, then the radiative forcing attributed to a given mass of emissions has grown over time, and the climate system’s response to soot reductions will differ from what single-compound models predict. Resolving black carbon subtypes in climate models, the authors argue, is essential for accurate estimation of black carbon’s contribution to observed warming and for projecting its future role.

The findings also carry a pointed message for mitigation policy. Not all black carbon sources are equal. Soot-rich sources, dominated by fossil fuel combustion in transport, industry and power generation, deliver far more warming per unit of emissions than char-dominated sources such as residential biomass burning. Prioritizing soot-rich sources for emission controls would therefore yield disproportionate climate benefits in the near term, a particularly attractive proposition given black carbon’s short atmospheric lifetime. Cutting soot-heavy emissions today produces almost immediate cooling, unlike reductions in long-lived greenhouse gases whose benefits unfold over decades to centuries.

The study also intersects with a broader and sometimes counterintuitive debate in aerosol–climate science. As societies clean up particulate pollution for public health reasons, some of the masking effect of reflective aerosols is lost, potentially accelerating near-term warming. Because black carbon is absorbing rather than reflecting, distinguishing its subtypes becomes even more important when weighing the climate consequences of air quality policies. A more absorbing black carbon burden means that the warming side of the aerosol ledger is heavier than previously assumed, sharpening the urgency of targeted controls on the most light-absorbing emissions.

By fusing thousands of laboratory and field measurements, a 270-year emission reconstruction, optical theory and Earth system modeling, the research delivers one of the most detailed portraits yet of how humanity has changed not just the quantity but the quality of the soot it injects into the atmosphere. The black carbon of the Anthropocene is darker, more absorbing and more warming than the black carbon of the age of sail and charcoal, and recognizing that evolution is a necessary step toward both sharper climate projections and smarter, faster-acting mitigation strategies.

Subject of Research: Historical increase in the global warming potential of atmospheric black carbon driven by a rising soot fraction from fossil fuel combustion since 1750

Article Title: Increase in global warming potential of atmospheric black carbon since 1750

Article References: Shen, H., Shen, H., Cheng, Y., Andreae, M. O., Jiao, X., Liang, X., Mai, Z., Guo, P., Zheng, L., Peng, X., Du, W., Wang, R., Zhang, G., Zhai, J., Zeng, Y., Sun, H. Z., Chen, Y., Wang, C., Huang, T., … Zhang, G. (2026). Increase in global warming potential of atmospheric black carbon since 1750. Nature Geoscience. https://doi.org/10.1038/s41561-026-02085-z

Image Credits: AI Generated

DOI: 10.1038/s41561-026-02085-z

Keywords: black carbon, soot, char, short-lived climate forcer, fossil fuel combustion, radiative forcing, mass absorption cross section, emission inventory, thermal-optical analysis, climate modeling, sediment records, Nature Geoscience