On Jan. 15, the International Global Atmospheric Chemistry Project issued a report detailing the role of black carbon in the atmosphere. According to the report, black carbon has nearly twice the direct climate impact as previously assessed, making it second only to carbon dioxide as a climate-warming agent. Tami Bond, a professor of civil and environmental engineering at the University of Illinois, is the first author of the study and a leading expert in black carbon emissions. She discussed the importance of black carbon and the new report’s findings with News Bureau physical sciences editor Liz Ahlberg.
What is black carbon? Why are atmospheric and climate scientists concerned about it?
Black carbon is a small, dark particle of soot that warms Earth’s climate. It’s the black smoke you might see coming from the tip of a candle or the back of a diesel truck. Black carbon is a particle rather than a greenhouse gas, but it is the second largest climate warmer, after carbon dioxide. Black carbon absorbs sunlight and heats the atmosphere. It also darkens snow and accelerates melting. It can change the brightness of water and ice clouds.
Unlike carbon dioxide, black carbon is quickly washed out and can be eliminated from the atmosphere if emissions stop. People are looking at it right now as a quick way to reduce climate warming – not a fix to the problem, but a way to reduce warming in the immediate future.
Where does black carbon come from, and where does it end up?
Black carbon comes from poor combustion. In the United States, its sources are mainly diesel engines and open forest burning. Other sources around the world include wood and coal burning in homes, some kinds of industry, kerosene lamps, and open savanna burning. Concentrations of particles are largest around cities, but black carbon travels as far as remote oceans and the Arctic.
What makes this study so important?
This is the first time that a group of experts has formally assessed the entire complicated influence of black carbon and its sources. The study found that black carbon has a much larger warming influence than had been assumed. Many models simulate lower absorption than observed in the atmosphere and thus underestimate warming by black carbon. It affects not only the atmosphere, but also clouds and snow, and the result is still warming.
The study also set up a framework for evaluating the total climate effect of each source. Combustion sources are complicated, and they emit other gases and particles in addition to black carbon. The study provides a basis to estimate the complex climatic impacts of mitigation actions. This framework is designed to be updated as the science of black carbon moves forward.
What policies or actions did the experts suggest or support in the study?
The study supports the idea that we can slow global warming a bit by reducing emissions from some black carbon sources. Those include diesel engines, some kinds of wood and coal burning, and industrial sources such as low-technology brick kilns. Cleaning up emissions would improve air quality and human health, and the climate benefits provide another reason to take actions that benefit many people. Both the immediate climate impact of air pollutants and the long-term climate change from greenhouse gases are important.
