Definitions

Short-Lived Climate Pollutants
Short-lived climate pollutants (SLCPs) are agents that have relatively short lifetime in the atmosphere - a few days to a few decades - and a warming influence on climate. The main short lived climate pollutants are black carbon, methane and tropospheric ozone, which are the most important contributors to the human enhancement of the global greenhouse effect after CO2. These short-lived climate pollutants are also dangerous air pollutants, with various detrimental impacts on human health, agriculture and ecosystems. Other short-lived climate pollutants include some hydrofluorocarbons (HFCs). While HFCs are currently present in small quantity in the atmosphere their contribution to climate forcing is projected to climb to as much as 19% of global CO2 emissions by 2050.
Black Carbon
Black carbon is a major component of soot and is produced by incomplete combustion of fossil fuel and biomass. It is emitted from various sources including diesel cars and trucks, residential stoves, forest fires, agricultural open burning and some industrial facilities. It has a warming impact on climate 460-1500 times stronger than CO2. Its lifetime varies from a few days to a few weeks. When deposited on ice and snow, black carbon causes both atmospheric warming and an increase of melting rate. It also influences cloud formation and impacts regional circulation and rainfall patterns. In addition, black carbon impacts human health. It is a primary component of particulate matter in air pollution that is the major environmental cause of premature death globally.
Methane
Methane (CH4) is a greenhouse gas that is over 20 times more potent than CO2, and has an atmospheric lifetime of about 12 years. It is produced through natural processes (i.e. the decomposition of plant and animal waste), but is also emitted from many man-made sources, including coal mines, natural gas and oil systems, and landfills. Methane directly influences the climate system and also has indirect impacts on human health and ecosystems, in particular through its role as a precursor of tropospheric ozone.
Hydrofluorocarbons
HFCs are man-made greenhouse gases used in air conditioning, refrigeration, solvents, foam blowing agents, and aerosols. Many HFCs remain in the atmosphere for less than 15 years. Though they represent a small fraction of the current total greenhouse gases (less than one percent), their warming impact is particularly strong and, if left unchecked, HFCs could account for nearly 20 percent of climate pollution by 2050.
Tropospheric Ozone
Tropospheric or ground level ozone (O3) is the ozone present in the lowest portion of the atmosphere (up to 10-15km above the ground). It is responsible for a large part of the human enhancement of the global greenhouse effect and has a lifetime of a few days to a few weeks. It is not directly emitted but formed by sunlight-driven oxidation of other agents, called ozone precursors, in particular methane (CH4) but also carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NOX). Tropospheric ozone is a harmful pollutant that has detrimental impacts on human health and plants and is responsible for important reductions in crop yields.