by Hannah Chang
Black carbon (“BC”), a component of soot and particulate matter, competes closely with methane as the largest anthropogenic contributor to global warming after carbon dioxide. BC emissions primarily result from four sources: burning of residential fuels such as wood and coal; open burning of land, whether natural or human-induced; diesel engines; and industrial processes, such as small boilers. One pound of BC is estimated to cause 700 times as much warming as one pound of carbon dioxide.
BC mitigation has been identified by some as the “lowest hanging of the low-hanging fruit” – an affordable, politically feasible, fast-action means to mitigate the warming temperatures caused by climate change. For one thing, BC can be mitigated both domestically and internationally by affordable technologies that already exist, such as diesel particulate filters and more efficient cookstoves. Additionally, such mitigation has nearly immediate effects, as BC remains in the atmosphere for mere days or weeks, in contrast to carbon dioxide, which remains in the atmosphere for a century or more.
Moreover, because BC has distinct local and regional impacts, its mitigation has tremendous public health and environmental co-benefits. Locally, exposure to the fine particles in soot produced from cookstoves, coal combustion, and diesel engines is associated with premature mortality from heart and lung disease. The World Health Organization estimates that indoor air pollution from cooking and residential heating causes 1.6 million premature deaths each year. Diesel particulate emissions are estimated to lead to over 21,000 premature deaths in the United States in 2010. Regionally, BC interacts with other aerosols to form “atmospheric brown clouds,” or hotspots of atmospheric solar heating, that have been identified in South Asia, eastern China, most of Southeast Asia, regions of Africa, Mexico and Central America, and parts of South America. Additionally, BC is swept only a relatively short distance from its source before falling out of the atmosphere where its absorption of sunlight contributes to rapid melting of any ice or snow on which it lands. Arctic sea ice is melting as much as a result of regional BC emissions as a result of warming caused by greenhouse gases, for instance, and BC is thought to have caused about one-third of the glacial retreat in the Himalayas.
In the United States, which contributes about 6% of the global total of BC emissions, diesel engines are the primary source of black carbon. Although the United States is a relatively small contributor to worldwide BC emissions, its per capita emissions are actually comparable to those in developing regions where the vast majority of BC is emitted. CCCL has posted a working paper available here, that brings a narrow focus to domestic mitigation of black carbon – outlining how emissions are and can be controlled under the Clean Air Act and identifying one way in which municipalities and states can contribute to mitigation.