Reducing CO2 emissions is essential to limit long-term warming but it cannot slow warming quickly enough to stay below 1.5°C or even 2.0°C by the 2050s.

While carbon dioxide (CO2) is the largest single contributor to current warming, responsible for about half of the warming, the non-CO2 climate pollutants are responsible for the other half.

Reducing CO2 emissions is essential to limit long-term warming but it cannot slow warming quickly enough to stay below 1.5°C or even 2.0°C by the 2050s. This is because when fossil fuels are burned, short-lived cooling aerosols are co-emitted as byproducts. A realistically paced phase-out of fossil fuels, or even a rapid one under aggressive decarbonization, is likely to have minimal net impacts on near-term temperatures because the removal of co-emitted aerosols will unmask the true magnitude of warming the planet is experiencing today.

The non-CO2 climate pollutants include the four short-lived climate pollutants (SLCPs or “super climate pollutants”)—methane (CH4), black carbon soot, tropospheric ozone (O3), and hydrofluorocarbons (HFCs)—as well as the longer-lived nitrous oxide (N2O). Because short-lived super climate pollutants only last in the atmosphere from days to 15 years, reducing them will prevent 90 percent of their predicted warming within a decade.

Reducing non-CO2 climate pollutants is the fastest way to reduce near-term warming over the next two decades and the only currently known way to slow the rate of warming in the near term, limit self-amplifying climate feedbacks, and avoid or at least slow irreversible tipping points.

Source: Climate & Clean Air Coalition (CCAC).

Fast Mitigation  

Mitigation strategies targeting non-CO2 climate pollutants can cut the rate of global warming in half

A fast phasedown of HFCs can avoid nearly 0.1°C of warming by 2050 and up to 0.5°C by the end of the century, according to the Quadrennial Scientific Assessment of Ozone Depletion (2018). The Assessment also calculated that the initial schedule of the Kigali Amendment to the Montreal Protocol will capture 90% of the potential (0.44°C; range 0.4-0.5°C) and that an accelerated schedule or leapfrog strategy can capture the rest. Promoting the energy efficiency of cooling technology during the switch to climate-friendly refrigerants would double these climate benefits.

Cutting anthropogenic methane emissions by 45% by 2030 can avoid additional warming of nearly 0.3°C by the 2040s, with the potential for significantly more avoided warming from emerging technologies to remove atmospheric methane faster than the natural cycle—with the potential of avoiding up to 0.6°C by mid-century.

Reducing anthropogenic N2O emissions by 50-75% by 2030 can avoid up to 0.05°C of warming by 2050.

These non-CO2 mitigation strategies comprise a fast mitigation sprint that can avoid four times more warming by 2050 than targeting CO2 alone, which is a longer-term marathon.

The good news is we have shovel-ready technologies and policy proposals at hand. Some of the quickest actions we can take include:

  • Require climate-friendly refrigerants and cooling equipment that are super energy-efficient. Cutting HFCs under the Kigali Amendment to the Montreal Protocol can avoid up to 0.5°C   of future warming.
  • Deploy soot-free diesel. Retrofit diesel vehicles fueled by ultra-low sulfur diesel with diesel particulate filters, on the way to electric vehicles and perhaps hydrogen for trucking.
  • Ban food waste from landfills. One-third of food waste is dumped in landfills. Along with other organic waste, it is one of the largest sources of methane, equivalent to the emissions of 37 million cars. The edible part of the food should be used to feed the hungry while the non-edible can be processed through biodigesters to produce renewable fuels.
  • Manage manure on farms. Reduce methane and other climate pollutants produced by cattle and other farm animals through feed additives and manure management including biodigesters that can produce renewable fuel as we shift our diet to depend less on farm-raised animals.
  • Fix pipeline leaks. Replace leaky equipment and ramp up monitoring and detection to reduce fugitive methane from transmission and distribution of natural, or fossil, gas.

Winning the super pollutant sprint is critical for staying within the limits of adaptation and for building resilience. 

Super Pollutants Resources