Short-Lived Climate Pollutants

An Initiative of the U.S. Climate Alliance

The U.S. Climate Alliance commits to reducing emissions of short-lived climate pollutants and challenges all national and subnational jurisdictions to do so as well and bring new commitments and actions to slash emissions of these “super pollutants” to the Global Climate Action Summit in September.


│ Potent “Super Pollutants” Have Big Climate, Health Impacts

Short-lived climate pollutants are potent climate forcers and harmful air pollutants that have an outsized impact on climate change in the near-term.  Compared to CO2 and other long-lived climate pollutants, which stay in the atmosphere for centuries, short-lived climate pollutants have far more warming impact on a gram-to-gram basis, and have a lifetime ranging from days (in the case of black carbon) to decades.  Reducing emissions of these pollutants can significantly reduce the rate of climate change in the near-term and is necessary for meeting the goals of the Paris Climate Agreement, along with significant reductions in carbon dioxide emissions.  Short-lived pollutants include:

  • Methane: Methane is responsible for about 20-25 percent of current global climate forcing and contributes to the formation of tropospheric ozone, which is itself a short-lived climate forcer and harmful to human health and agricultural production. As the primary component of natural gas, capturing and utilizing methane improves health and safety and offers billions of dollars in potential value in the U.S. Quickly reducing methane emissions offers one of the greatest opportunities to reduce global warming in coming decades.

  • Hydrofluorocarbons (HFCs): HFCs are used as refrigerants and in air conditioning, foams, aerosols, and other applications. They are the fastest growing source of greenhouse gas emissions in the U.S. and globally, and are thousands of times more potent than CO2. Coupled with efficiency opportunities in refrigeration and cooling, phasing down the use of HFCs can deliver significant climate and energy efficiency benefits.

  • Black carbon: Black carbon, or soot, is a component of toxic particulate matter, which is a leading environmental and health hazard. Black carbon accelerates snowmelt and sea level rise and modifies rainfall patterns. As a component of fine particulate matter, it causes millions of premature deaths globally each year and is harmful to the human cardiovascular and respiratory system. Black carbon exists in the atmosphere for days, so emissions reductions deliver immediate climate and local health benefits.

│ Tremendous Opportunity and Benefits

The Emissions Gap Report 2017 by the United Nations Environment Programme suggests that a collection of cost-effective strategies could virtually eliminate HFC emissions by 2035 and reduce emissions of methane by about one-third and black carbon by 70 percent below current levels by 2030 – both in the U.S. and globally.  Additional strategies targeting “super emitters” (a small fraction of sources responsible for a relatively large share of emissions) and to reduce methane from agriculture and waste could lead to significant additional methane reductions.  According to the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants (CCAC), putting these measures in place could avoid over 2 million premature deaths and 50 million tons of crop losses each year, cut the expected rate of global warming in half through 2050, and significantly slow sea level rise. 

│ Economic Opportunity in Alliance States

In Climate Alliance States and the U.S., reducing short-lived climate pollutant emissions can support economic growth and jobs in the agricultural, energy, industrial, transportation, and waste sectors.  It can support health and prosperity in rural and urban economies alike.  For example:

  • Dairy and swine farms in Alliance states could support thousands of anaerobic digesters producing renewable gas and other products worth billions of dollars per year. An estimated 2,500 projects can be supported on farms in California, Minnesota, and North Carolina alone.

  • The U.S. EPA estimates that about 45 percent of coal, oil, and gas methane emissions can be reduced nationally at low or negative cost. The International Energy Agency and EDF have similarly found that nearly half of methane emitted from oil and gas operations in the U.S. and globally can be reduced at essentially zero net cost. Capturing these emissions can improve mine and pipeline safety, conserve energy, and save money.

  • Alliance states are home to more than 250 landfill energy projects that consume methane that would otherwise be emitted or flared, and opportunities exist for nearly 100 more.

  • Strategies to reduce HFC emissions promote more energy efficient systems that lower costs for businesses and households, support the leadership of U.S. businesses developing alternatives to HFCs, and increase the need for skilled technicians and system designers. Phasing down the use of HFCs could create tens of thousands of jobs and tens of billions of dollars in annual economic value in the U.S.

│ Building on Leading Activities in States

On September 13, 2018, The U.S. Climate Alliance released the From SLCP Challenge to Action road map.  In the coming months, U.S. Climate Alliance members will formulate specific plans and commitments to significantly reduce short-lived climate pollutants and capture individual and collective opportunities to support economic growth and improve public health.  Many Climate Alliance States already have activities under way:

  • California law requires reducing emissions of anthropogenic black carbon by 50 percent, and methane and HFCs by 40 percent, below 2013 levels by 2030. The State has developed a comprehensive Short-Lived Climate Pollutant Reduction Strategy to meet these goals, and has a number of regulatory, incentive, and workgroup efforts to meet these targets – including in the agricultural, oil and gas, and waste sectors. Recently, California became the first state to adopt regulations prohibiting the use of certain HFCs in some end uses.

  • Colorado was the first state to regulate methane emissions from oil and gas operations. The 2014 rules will prevent an estimated 65,000 tons per year of methane and ethane emissions and reduce emissions of volatile organic compounds by more than 93,000 tons per year. The climate benefits from the rule are equivalent to taking 310,000 cars off the road each year. A two-year pilot project in 2013-2015 found that infrared camera inspections reduced the incidence of leaks by more than 70 percent.

  • Connecticut includes anaerobic digesters in its Renewable Portfolio Standard and has an ongoing anaerobic digestion pilot program.

  • Massachusetts is the first state in the country to impose annually declining methane emissions limits (for 2018, 2019, and 2020) on natural gas distribution system operators, through regulations promulgated by the Massachusetts Department of Environmental Protection in 2017. In addition, the Massachusetts Department of Public Utilities reviews and approves annual plans developed by the natural gas distribution system operators, prioritizing the replacement of leaky pipelines and service lines.

  • New York has developed a Methane Reduction Plan, including 25 measures across 5 agencies, to cut methane from oil and gas infrastructure, waste management, and agriculture. In his 2018 State of the State, Governor Cuomo directed New York agencies to develop a similar, comprehensive plan to reduce HFC emissions through a suite of regulatory, incentive, and capacity-building programs.

  • Vermont’s Universal Recycling Law contains an organics diversion mandate to reduce landfill methane generation, which is complemented by organic waste reduction and diversion goals in the state’s 2014 Materials Management Plan. The State is addressing fine particulate matter and black carbon emissions through its Clean Diesel Grant Program – which provides technical assistance and incentive funding for projects that reduce diesel emissions from engines, vehicles, and equipment in Vermont – and periodic wood stove change-out programs for the removal and replacement of uncertified wood heaters with lower-emitting alternatives.

  • Washington State law HB 2580 creates a suite of financial incentives and market support for renewable natural gas, including developing pipeline quality standards and a set of recommendations to support market development.

│ Widespread Support for Action

There is widespread support for reducing emissions of short-lived climate pollutants among businesses, governments, and other organizations.  This includes commitments from major oil, gas, and chemical companies and their coalitions, the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants, the Under2 Coalition, the entire international community under the Kigali Amendment to the Montreal Protocol, and many more.  The Climate Alliance will work with these and other interested organizations to expand action and develop tools and strategies to reduce emissions of these potent pollutants. 



This Roadmap takes our commitment from SLCP Challenge to Action.  It outlines a menu of options states will consider as we pursue an ambitious set of goals that have the potential to reduce SLCP emissions in the U.S. Climate Alliance as a whole by 40-50 percent below current levels by 2030.  States will develop individual SLCP reduction strategies, continue to share information and best practices, develop and improve emissions inventories to track progress, and pursue partnerships to expand action on SLCPs and meet the goals of the SLCP challenge.  The U.S. Climate Alliance will track and annually report on progress towards its SLCP reduction goals.