Multi-core black carbon packs extra warming power

Traditionally, black carbon (BC) particles – such as those produced by wildfires – have been represented in global climate simulations as simple “core–shell” structures, with a single carbon core at the centre surrounded by outer layers. However, an international and interdisciplinary research team, including a scholar from FLASS, has found that in long-range transported wildfire smoke, about one fifth (21%) of black carbon particles — especially those larger than 400 nm in diameter — contain two or more cores.

Because these “multi-core” BC aerosols from wildfires absorb significantly more sunlight than their single-core counterparts, their presence may help explain why global climate models consistently underestimate BC’s light absorption by around 50% compared with observational measurements.

The discovery was made by an international team led by Professor Li Weijun from the School of Earth Sciences at Zhejiang University, with members including Dr Joseph Ching Ping-pui from the Department of Science and Environmental Studies (SES). The team’s findings were published in Nature Communications in November 2025 under the title “Locating the missing absorption enhancement due to multi‒core black carbon aerosols”.

Previous theories suggested that BC “ages” primarily by accumulating additional coating layers in the atmosphere. As a result, climate assessments have long assumed that each particle contains only one core. Through fieldwork conducted during Yunnan’s wildfire season, combined with advanced electron microscopy, the research team found that BC particles can collide and coalesce, forming clusters with multiple cores within a single particle — often exceeding 200 nm in total core diameter.

Black carbon aerosols are among the strongest light absorbers in the atmosphere and a major driver of global warming. Lead author Dr Chen Xiyao noted, “The mixing state of BC is fundamental to understanding its climate effects. Ignoring coagulation and multi-core structures prevents accurate assessment and policy development regarding BC’s role in climate change.”

To evaluate the impact of multi-core particles, the team developed a machine learning emulator for absorption enhancements and incorporated it into a global atmospheric model. Their simulations showed that multi-core BC contributes to a 19% increase in global average of BC’s light absorption, particularly in wildfire-affected regions such as Southeast Asia, southwestern China, the Tibetan Plateau, Southern Africa, and North America.

Corresponding author Professor Li Weijun explained, “Our nanoscale observations revealed abundant multi-core BC particles in both wildfire and urban environments — structures previously absent from climate models. By refining our algorithms, we simulated their enhanced optical absorption and quantified their contribution to global warming, enabling more precise evaluation of BC’s climate impact. This work strengthens the scientific basis for climate governance and global cooperation.”

Dr Joseph Ching, Assistant Professor in SES, who played a pivotal role in the atmospheric modelling, added that combining particle-level imaging, optical simulations, global climate modelling, and machine learning significantly advances understanding of BC’s warming effects. “This integrated approach moves researchers closer to accurately assessing BC radiative forcing and supports the development of more effective climate policies,” Dr Ching said.

The authors recommend that future climate models incorporate BC’s multi-core mixing state to improve the accuracy of global radiative forcing estimates and inform emission reduction strategies. Co-author Professor Mark Jacobson of Stanford University emphasised that the study reinforces black carbon’s position as the second-largest contributor to global warming, underscoring the urgency of mitigation.

Widefires are becoming increasingly devastating and costly. According to global reinsurer Munich Re, half of the fires costing US$1 billion or more among the 200 most damaging since 1980 occurred in the past decade. Understanding the true impact of the BC particles produced by wildfires is therefore essential for evaluating their effects on the climate system and developing effective solutions.

Given the expected rise in wildfire activity and anthropogenic emissions under continued global warming, integrating these insights is crucial for effective climate governance and international collaboration. The study also contributes to the United Nations Sustainable Development Goals (SDGs), particularly Goals 3 (Good Health and Well-being), 11 (Sustainable Cities and Communities), and 13 (Climate Action).

The international research team includes scholars from Chinese Mainland, Hong Kong, the United States, the United Kingdom, Israel, Japan, and South Korea, spanning atmospheric science, global climate modelling, electron microscopy, atmospheric environment, air pollution, and earth system science.

Click here to read full article published in Nature Communications.