To effectively combat climate change, we must address all greenhouse gases and pollutants contributing to global warming—not just carbon dioxide (CO₂). Super pollutants (SPs) in particular represent a viable option for near-term mitigation, and one that is often underappreciated. While perhaps not as photogenic as other carbon projects, containing super pollutants such as methane, black carbon, N₂O, hydrofluorocarbons, and ozone-depleting substances can help to meet near-term warming and avoid dangerous tipping points. 

While they are relatively short-lived in the atmosphere compared to CO₂, super pollutants are responsible for approximately half of the warming observed today.^[1] The Climate and Clean Air Coalition (CCAC) describes super pollutants as a “flow” problem—driving the rate of warming—whereas CO₂ represents a “stock” problem, determining the ultimate extent of warming. Tackling these pollutants alongside CO₂ is essential to achieving the Paris Agreement’s goal of limiting global warming to 1.5°C. 

All good so far, but who pays? How do we get these projects up and running quickly? How can we ensure they deliver the desired benefits?

Today, carbon markets incentivize the mitigation of super pollutants, but at a scale that is yet to be fully realized. So much more can and must be done to contain these emissions. To reach the full mitigation potential, we need high-integrity super pollutant methodologies, as well as the full suite of measurement, reporting, and verification systems. We need more project developers, and we need more buyers. The CC Lab is particularly excited about Google's recent efforts in this space, which include expanding its portfolio of carbon credits to include HFCs and landfill gas projects, and emphasizing the vitality of curbing super pollutants.^[2] What is so interesting about the Google announcement is that they are not just buying credits off the shelf, but are actively helping to build new projects, providing both upfront financing and forward offtake. This helps the projects get started and shows a clear and positive impact. 

Of course, carbon markets are not the only source of financing or lever for change that we need to bring. Admittedly, carbon markets have a chequered history, and we need to guard against sending the wrong signals and unintended consequences. But while policymakers and innovators work on ways to meet climate stabilization goals, carbon markets can help fund new projects and mitigation pathways.

When we founded the CC Lab in January of 2020, we created an in-house database of carbon market methodologies. We knew that deep insight can be had from those who have tried—the hard way—to develop these methodologies. We are also just curious people who love research and categorizing disparate information into searchable databases.

In the language of carbon markets, a “methodology” is a core standard that governs a type of project, providing a scope of activities, and importantly, formulae for issuing credits. Methodologies are typically issued by registries and follow common standard-setting procedures to be developed, including peer review and public comment. Methodologies (or associated standards issued by the registries) usually describe the measurement, verification, and reporting activities that are required, and other rules to determine whether a project can be eligible to sell a tradable credit for the activity type that the methodology covers. All told, methodologies are key tools that define the volume and quality of carbon credits being issued. 

With the great work of multiple analysts and interns over the years, the CC Lab’s methodology database now tracks all known carbon market methodologies available worldwide—those current, those defunct, and those in development, covering both compliance and voluntary markets. As of today, there are over 400 methodologies across 18 registries in our database, and 143 methodologies that directly address super pollutants. Of these, 109 are currently active and 4 are in the draft stage.

One of the draft methodologies is our very own. The CC Lab’s Methodology for Recovery and Destruction of Hydrofluorocarbons in Article 5 Countries is currently under review with OneShot.Earth Open Carbon Protocol system^[3], as well as forming the basis for the GHR001 methodology for HFC destruction^[4] at the Global Heat Reduction Initiative. This methodology is being used by Recoolit in Indonesia, and in turn, Recoolit’s credits will be bought and retired by Google to meet its climate commitments.

The rest of this article gives a snapshot of the methodologies that are currently available for the super-pollutants: methane, N₂O, F-Gases (HFCs and ODS), and black carbon. We do not review these for quality, regional uptake, or scale of their use in terms of the number of credits issued, although we intend to tackle this in the future. 

100-year vs 20-year Global Warming Potentials (GWP)

Given the relatively short atmospheric lifetimes of super pollutants, the choice of emission metric is crucial when issuing carbon credits. Since one credit represents the reduction, avoidance, or removal of one tonne of carbon dioxide equivalent (CO₂e), the selected Global Warming Potential (GWP) significantly influences the calculated climate impact of each gas. As a result, the choice of the GWP metric directly affects the volume of credits a project can generate. While issuing methodologies, it’s standard practice to use the 100-year GWPs, which implies a long-term approach to mitigation. However, we believe that the use of 20-year GWPs would better represent the short-term super-polluting impact of these gases. For more on emissions metrics and why they matter, see our blog post from 2023.^[5]

Methane is a short-lived climate pollutant with a global warming potential (GWP) of 81.2 over a 20-year period and 27.9 over a 100-year period.^[6] Today, methane emissions have already caused 0.51°C of the 1.06°C of total observed warming since the Industrial Revolution.^[7] Reducing methane emissions is one of the fastest ways to slow global warming, and will prevent hundreds of thousands of premature deaths, asthma-related hospital visits, billions of hours of lost labor from extreme heat, and millions of tonnes of crop losses globally.^[8] 

Out of all the super pollutants, methane currently has the widest coverage in the carbon market. To date, we have found 81 active methane methodologies, with 3 additional methodologies in draft form (shown in Figure 2 below). Additionally, there are 23 methodologies that have been marked as either inactive or on-hold across the registries. 

The CC Lab mapped the landscape of F-Gas-related methodologies and projects in 2023, noting a gap for HFC destruction, which you can read about on our website.^[9] Subsequently, we developed a draft methodology, which is included in Figure 3 above. 

The CC Lab and its collaborators continue to find new circumstances and pathways that could benefit from climate finance, and are actively exploring several areas for new methodologies, and ways in which buyers can step up their support for expanding and motivating new project development, and therefore, containment of these potent gases.

N₂O is a unique and hazardous super pollutant for several reasons. First, it has an exceptionally long atmospheric lifetime—about 109 years—making it the only super pollutant that is not also classified as a short-lived climate pollutant. Second, according to the IPCC's Sixth Assessment Report (AR6), N₂O uniquely has the same GWP–273–over both 20-year and 100-year timescales.^[6] 

In addition to its climate impact, it is a significant ozone-depleting substance. Primarily emitted from agricultural activities, industrial processes, and combustion, it is both highly stable in the atmosphere and highly potent, amplifying its long-term effects on the climate and the stratospheric ozone layer. According to the Institute for Governance & Sustainable Development, reducing anthropogenic N₂O emissions by 50-75% by 2030 can avoid up to 0.05°C of warming by 2050.^[10]

Black carbon forms through the incomplete combustion of fossil fuels or biomass, and is a major contributor to health as well as climate change. It is estimated that some 5.8 million tonnes of black carbon were emitted in 2019.^[11] Black carbon is not a gas, but contributes to warming directly by particulate matter absorbing sunlight and releasing it as heat, warming the air and surfaces in the regions where it is concentrated; and indirectly through altering the albedo of surfaces, especially in the cryosphere, and through cloud interactions. Black carbon has a short atmospheric lifetime (of 4-12 days) with a high associated GWP and very large human health impacts. Global warming impacts are, however, highly localized and hard to quantify. Complicating factors include differing atmospheric lifetimes, the geographic location of emissions, altitude, cloud interactions, the presence of co-emitted pollutants, and the influence of aging and mixing processes in the atmosphere.

Given these measurement complications, it is perhaps unsurprising that we found only one carbon market protocol, The Gold Standard’s “Emission Reductions of Black Carbon and Co-Emitted Species from Improved Efficiency Cookstoves”, that directly generates credits for black carbon (BC) emission reductions. Otherwise, there are no explicit carbon crediting protocols for BC, although at least 25 other methodologies directly refer to the co-benefit of reducing black carbon for associated emissions reductions. Additionally, we identified 156 active methodologies with the potential to deliver black carbon (BC) reductions as a co-benefit. These span a range of activity types, including clean cookstoves, avoided biomass burning, reduced flaring, electrified transportation, biofuel production, industrial and building efficiency, and renewable energy development.

While there is a wide range of methodologies for super pollutants, there are still some important mitigation pathways that do not have active methodologies today. Future publications of the CC Lab will aim to identify these topics that we think make sense for carbon markets to play a role. 

One challenge that we experienced firsthand is that methodologies are both difficult to write and can take a long time to pass through all the relevant procedures, review processes, and public comment steps. Speeding this process up while also maintaining rigor and access is imperative to meet the moment and the climate imperative to deal with super pollutants. Given this pressure, we are pleased to see newer registries like the Global Heat Reduction Initiative and OneShot.Earth rise to the challenge to tackle super pollutants, just as we are pleased to see Isometric and Puro.Earth registries do the same for carbon dioxide removal. The carbon market is converging around core principles for quality, with the rise of project ratings organizations like BeZero and Calyx, and oversight and guidance coming from the ICVCM’s Core Carbon Principles. 

In addition to carbon markets–and sometimes instead of them–it makes more sense for value-chain projects, regulation, extended producer responsibility, and/or other financing mechanisms to motivate the containment of super pollutant emissions. We need an “all of the above” approach to finance climate action and to ensure we can contain more emissions, sooner.