What are SLCPs?

The term "SLCPs" stands for Short-lived Climate-forcing Pollutants.

Some call them "short-lived climate pollutants" or "short-lived climate forcers" which is then abbreviated as SLCF. In general, all terms refer to the same group of substances, but some publications or groups might refer to only a subset of substances.

In brief, SLCPs include:

  • particulate matter and precursor gases (soot, nitrate, sulfate, ammonium, organic carbon and other compounds such as sulfur oxides and nitrogen oxides)
  • ground-level ozone and its precursors such as nitrogen oxides, carbon monoxide and volatile organic compounds
  • methane
  • and hydrofluorocarbons (HFCs)

Ground-level ozone and particulate matter are mostly known as classical air pollutants. But SLCPs are also key players in climate change - some have warming and some have cooling effects. Altogether, they cause millions of premature deaths every year resulting from outdoor and indoor air pollution, and they reduce agricultural productivity by more than 30 million tons per year (UNEP 2011).

Why “short-lived”? CO2 remains in the atmosphere for a hundred years or more, while SLCPs have much shorter lifespans. Black carbon and ground-level ozone, for example, are removed from the air within a range from several hours to a few days. Methane can stay in the atmosphere for about 10 years and HFCs have a wide range of lifetimes from one year to 30 years or more. Those who are familiar with the Assessment Report from 2007 of the Integrated Panel on Climate Change (IPCC) may notice that methane and halocarbons were classified as long-lived greenhouse gases just like CO2. However, time periods that matter for statistical considerations of climate are at least 30 years long, and changes in the emissions of shorter-lived gases will lead to comparatively rapid atmospheric changes. From that perspective also methane and HFCs can be considered short-lived.

Why “climate-forcing”? All of the SLCPs have an effect on Earth's radiative balance and thus influence temperature. To find out about the specific mechanisms of how each substance affects temperature, click on the name of the substance in the left-hand menu.

Why “pollutants”? SLCPs do not only have adverse effects on the Earth's climate but they also have negative effects on human health, in particular, close to where they are emitted or formed. Especially particulate matter (very small particles) and low-level ozone (a gas) affect the respiratory and cardiovascular systems and may cause acute or chronic diseases which can lead to premature death.

The figure below illustrates how long the different substances grouped under the term ‘SLCPs’ remain in the atmosphere (vertical axis) and how far they can be transported (horizontal axis). The longer a substance remains in the atmosphere, the farther it can be transported. CO2, for example, is transported globally and therefore is very well mixed in the atmosphere. Methane and HFCs (box in the middle of the graph) with lifespans in the order of several years are transported hemispherically and globally and are thus fairly well mixed, too. The other gases and particles (bottom left box), however, cannot be transported very far because they are removed from the atmosphere rather quickly, within hours or several days. Therefore, their effects occur primarily locally and regionally. Another special aspect of these substances is that, aside from their effect on the climate, they have a direct, negative impact on health and ecosystems.