What are 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.
Why do we need to act?
Short-lived climate pollutants are impacting public health, food, water and economic security of large populations, both directly through their impacts on human health, agriculture and ecosystems, and indirectly through their effects on climate. Short-lived climate pollutants have become a major development issue that calls for quick and significant worldwide action.
Slowing down near-term global warming
Many regions are already suffering from accelerated climate change. Over the world glaciers are melting, weather patterns changing and sea levels rising while the threat of overshooting the 2ºC "safety" target is looming. Due to their short lifetimes, compared to CO2 which remains in the atmosphere for approximately a century, actions to reduce emissions of short-lived climate pollutants will quickly lower their atmospheric concentrations, yielding a relatively rapid climate response. Fast action to reduce short-lived climate pollutants, especially methane and black carbon, has the potential to slow down the warming expected by 2050 by as much as 0.5 Celsius degrees. However, if mitigating short lived climate pollutants will help to reduce the rate of global warming and avoid exceeding the 2°C target over the near term, long-term climate protection requires deep and rapid cut in carbon dioxide emissions.
Figure 1: Temperature benefits from black carbon and methane mitigation.
Potential temperature benefits from the 16 measures identified in the Integrated Assessment of Black Carbon and Tropospheric Ozone.The uncertainty of the temperature projections in 2070 is shown by the lines on the right hand side.
Source: UNEP/WMO, (2011), Integrated Assessment of Black Carbon and Tropospheric Ozone, Summary for decision makers, pp12.
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Avoiding millions of premature deaths
Each year, 3.1 million people die prematurely from indoor and outdoor air pollution. Short-lived climate pollutants are largely to blame. Fast actions on short lived climate pollutants, such as the widespread adoption of advanced cookstoves and clean fuels, have the potential to prevent over 2 million of premature deaths each year.
Increasing crop yields
Feeding a growing world population has become one of the major issues of our century and we cannot afford to lose millions of tons of crops each year because of air pollution. Present day global relative yield losses due to tropospheric ozone exposure range between 7-12 percent for wheat, 6-16 percent for soybean, 3-4 percent for rice, and 3-5 percent for maize . In addition, black carbon influences the formation of clouds that have a negative effect on photosynthesis that impacts plants growth. Rapidly reducing short-lived climate pollutants, for instance through the collection of landfill gas or the recovery of methane from coal mines, has the potential to avoid the annual loss of more than 30 million tons of crops.
Additional gains from mitigating hydrofluorocarbons (HFCs)
HFCs are man-made fluorinated greenhouse gases used as replacements for ozone-depleting substances (ODS). These chemicals have no known natural sources, and they are being used in the same applications where ODS have been used: air conditioning, refrigeration, fire suppression, solvents, foam blowing agents, and aerosols. Most importantly, HFCs are rapidly increasing in the atmosphere. Though HFCs currently represent a small fraction of total greenhouse gases, their warming impact is particularly strong, and their emissions are projected to increase nearly twentyfold in the next three decades if their growth is not reduced. The most commonly used HFC is HFC-134a, which is 1,430 times more damaging to the climate system then carbon dioxide.
Emissions of HFCs are growing fast. As a result, HFCs emissions could offset much of the climate benefits from the Montreal Protocol. They are projected to rise to about 3.5 to 8.8 Gt CO2eq in 2050, comparable to total current annual emissions from transport, estimated at around 6-7 Gt annually. There are options available that could avoid or replace high-GWP HFCs in many sectors and also ways to reduce emissions
