Chemically, black carbon (BC) is a component of fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter). Black carbon consists of pure carbon in several linked forms. It is formed through the incomplete combustion of fossil fuels, biofuel, and biomass, and is one of the main types of particle in both anthropogenic and naturally occurring soot. Black carbon causes human morbidity and premature mortality. Because of these human health impacts, many countries have worked to reduce their emissions, making it an easy pollutant to abate in anthropogenic sources.

In climatology, black carbon is a climate forcing agent contributing to global warming. Black carbon warms the Earth by absorbing sunlight and heating the atmosphere and by reducing albedo when deposited on snow and ice (direct effects) and indirectly by interaction with clouds, with the total forcing of 1.1 W/m². Black carbon stays in the atmosphere for only several days to weeks, whereas potent greenhouse gases have longer lifecycles, for example, carbon dioxide (CO₂) has an atmospheric lifetime of more than 100 years. The IPCC and other climate researchers have posited that reducing black carbon is one of the easiest ways to slow down short term global warming.

The term black carbon is also used in soil sciences and geology, referring either to deposited atmospheric black carbon or to directly incorporated black carbon from vegetation fires. Especially in the tropics, black carbon in soils significantly contributes to fertility as it is able to absorb important plant nutrients.