Short-Lived Climate Pollutants

Short-lived climate pollutants (SLCPs) are warming agents that remain in the atmosphere for relatively short periods compared with the long-lasting influence of carbon dioxide. They include methane, black carbon, tropospheric ozone and many hydrofluorocarbons. Reducing their emissions can lower their atmospheric abundance relatively quickly, weakening their contribution to near-term warming.

Why shorter lifetimes produce a faster response

The amount of a pollutant in the atmosphere depends on both its emissions and how quickly natural processes remove it. When emissions of a short-lived pollutant fall, removal processes can bring down its atmospheric concentration relatively quickly.

• Methane is removed mainly through chemical reactions in the atmosphere, so sustained emission reductions can reduce its warming influence sooner than comparable action on a persistent pollutant.
• Black carbon particles are removed through processes such as rainfall and deposition, allowing their atmospheric abundance to respond rapidly to emission cuts.
• These pollutants exert substantial radiative forcing, meaning that they alter Earth's energy balance; reducing their abundance can therefore slow the rate of warming in the near term.

How the main pollutants cause warming

SLCPs do not all warm the climate in the same way, so mitigation must address their different sources and properties.

• Methane is a greenhouse gas emitted by sources including livestock, waste disposal and fossil-fuel production; it also contributes to the formation of tropospheric ozone.
• Tropospheric ozone is a warming greenhouse gas formed through atmospheric reactions involving precursor pollutants, rather than being emitted directly.
• Black carbon is a light-absorbing particle produced by incomplete combustion; it warms the atmosphere and can accelerate melting when deposited on snow and ice.
• Hydrofluorocarbons (HFCs) are greenhouse gases used in applications such as refrigeration and air conditioning; many have high warming potency, although their atmospheric lifetimes vary.

What rapid mitigation can and cannot achieve

SLCP mitigation complements, rather than replaces, carbon dioxide mitigation. Some of the carbon dioxide released today continues to influence climate for centuries, so controlling long-term warming requires sustained reductions in carbon dioxide emissions as well.

• Measures include preventing methane leaks, improving waste management, reducing soot from combustion and replacing high-warming refrigerants with suitable alternatives.
• Reducing black carbon and ozone pollution can also provide air-quality benefits, including protection of human health.
• Rapid benefits require sustained emission reductions; SLCP control alone cannot offset continued accumulation of long-lived greenhouse gases.