A 2013 scientific assessment of black carbon emissions and impacts found that black carbon is
second to carbon dioxide in terms of its climate forcing. Black carbon is 3,200 times more effective
on a mass-equivalent basis than carbon dioxide in causing climate impacts within 20 years, and 900
times more effective within 100 years. Black carbon increases global and regional temperatures
when emitted into the atmosphere, where individual particles directly absorb energy from the sun
and radiate it back as heat. Black carbon also reduces the strong cooling effect of large, highly
reflective surfaces such as glaciers and Arctic ice. High concentrations of black carbon in the
atmosphere can change precipitation patterns and reduce the amount of radiation that reaches the
Earth’s surface, which affects local agriculture.
Acute and chronic exposures to particulate matter are associated with a range of diseases,
including chronic bronchitis and asthma, as well as premature deaths from cardiopulmonary disease,
lung cancer, and acute lower respiratory infections. In 2012 the International Agency for Research
on Cancer re-categorized diesel engine exhaust as carcinogenic to humans based on evidence that
sufficient exposure is associated with an increased risk of lung cancer. Particles containing black
carbon are predominantly less than 100 nanometers in diameter, allowing them to penetrate deep
into the lungs and deliver toxic components to the bloodstream.