Black Carbon (BC) is an aerosol that forms from incomplete combustion of fuel, mainly through diesel emissions and burning of organic matter for cooking and heating.

BC has been gaining more attention recently as it is now considered the second largest contributor to global warming, behind carbon dioxide (CO2). BC is also gaining attention as reducing BC emissions will have a more immediate effect on global temperatures. This is because BC stays in the atmosphere for only several days to weeks, whereas CO2 can remain in the atmosphere for up to a hundred years.

Another important aspect of BC emissions is that their warming effects are localised, and therefore can produce changes in weather patterns by influencing atmospheric convention and large scale circulation. The localised emission of BC and other aerosols produces Atmospheric Brown Clouds (ABCs) which can have a direct effect on reducing local rainfall.

The advantage of considering BC emissions is that immediate emissions reductions can be made using current technology, and such reductions will also have other benefits for development and health.

The focus of BC emissions reductions in developing countries can generally be divided into open burning sources (e.g. forests, crop residue, savannah) and ‘contained’ combustion sources (e.g. household stoves, diesel vehicles, coal-powered industry). The latter category is particularly important in the short term as elevated indoor exposures to these emissions, such as in-door fires, represent one of the largest sources of premature mortality and illness in developing countries. Simple measures, such as the use of smokeless biomass stoves and solar lighting can have an immediate impact on public health, economic development and climate change. In developed countries, the focus is on reducing diesel emissions.

Reducing emissions from black carbon is not the solution to reducing global warming, but rather is part of a package of efforts to tackle the problem from all fronts. BC reductions are not a substitute for reductions in emissions of CO2, but instead are one among a range of strategies needed to meet climate change mitigation targets. To treat them as substitutes to CO2 emission reductions would deny the seriousness of the global threat of climate change.

However, bringing black carbon into climate strategy expands the choices of pathways for emissions reductions over time. In addition, addressing BC now may buy critical time to address CO2 emissions, which should remain the anchor of immediate climate mitigation efforts, but which policymakers have so far failed to address quickly enough.

Climate science tells us that tipping points for abrupt climate change may be imminent, which makes speed of the essence. Therefore UNEP is promoting immediate action on BC emissions based on current technology and existing international mechanisms while continuing to support the negotiating process for a wider climate change agreement with binding targets.