Ozone Depleting Substances


Certain gases used as refrigerants and foams are classified as “Ozone Depleting Substances”, or ODS. When they enter the atmosphere, these gases can warm the earth at a rate that is orders of magnitude above carbon dioxide (CO2). Although the production of many of these gases is banned under the Montreal Protocol, large quantities of ODS still exist in appliances or stockpiles. If these gases are not properly disposed of, most will eventually leak or be released into the atmosphere. Organizations can find and destroy these gases, generating emissions credits in the process.

We find these offsets to be among the most credible on the market. We currently recommend one ODS-destroying organization, Tradewater, which sells offsets directly from its website.

ODS as a carbon offset

Although CO2 is the most well-known greenhouse gas, other substances released into the atmosphere by human activity also have warming potential. Some of the most powerful warming gases come from refrigerants and foams and can have up to 10,000 times the warming effect of CO2. These include Chlorofluorocarbons (CFCs) and Hydrofluorocarbons (HFCs), which are sometimes found in aerosols, refrigerators, and air conditioners. As many of these substances deplete the ozone layer, they are frequently described as “Ozone Depleting Substances” (ODS).

Production of these chemicals is banned under the universally ratified Montreal Protocol (including the Kigali Amendment in 2016), but large quantities still exist, and the use of pre-existing ODS is not banned in most countries. If not destroyed, ODS will continue to leak from appliances and storage containers, entering the atmosphere and adding to warming. Project Drawdown also identifies refrigerant management as one of the most promising interventions to reduce warming.

In theory, ODS destruction is an attractive avenue for carbon offsets. There is no commercial value to ODS destruction, so this problem is unlikely to be solved in the absence of further government regulation, philanthropic donations, or carbon offsets. At this time, there are still plenty of ODS in circulation that needs to be found and destroyed. Because ODS-destruction projects can be ramped up semi-linearly with funding (i.e. they do not require large upfront capital investments but instead something like 1-1 investment per unit of ODS destroyed), revenue from selling offsets from a previous project can easily be reinvested in more ODS destruction.


There are a few elements to establishing causality of ODS destruction projects:

  • Conversion of ODS into less harmful substances

  • Establishing the counterfactual of ODS release into the atmosphere

  • Ensuring that destruction of ODS does not lead to more production of harmful gases

  • Accounting for the carbon footprint of the removal activities

We tackle each in more detail below.

Conversion of ODS into less harmful substances

ODS-destruction projects reduce GHGs by incinerating the ODS, converting them into substances with lower warming potential. While measuring the exact amount of gases destroyed is straightforward, converting this into the amount of CO2-equivalent gas removed requires understanding the “global warming potential” (GWP) of various gases. These have been established by the IPCC, who are consistently updating their lists of conversion factors [1]. Depending on the gas being destroyed, incinerating ODS can lead to thousands of times less warming over 100 years than simply letting the gases escape. Giving Green is not in a position to verify the science behind these conversion factors, but we believe we can trust the IPCC estimates.

Establishing the counterfactual of ODS release into the atmosphere

Another important factor in determining whether the condition of additionality is met is to understand whether ODS gases would have escaped if they had not been destroyed, or would have been sequestered indefinitely in canisters and appliances. Even under the best conditions, many ODS storage containers will slowly leak into the atmosphere and improper end-of-life disposal can result in complete release. The offset certifiers have standard assumptions for leakage over time. For instance, the Verra protocol allows projects to claim 100% of destruction to be additional when ODS are recovered from appliances at their end-of-life, and 25% when they are recovered from canisters that could be sold into the market and or sit unused in a warehouse. We believe these are reasonably conservative assumptions, and therefore accept them for offset projects that we analyze.

Ensuring that the destruction of ODS does not lead to more production of harmful gases

Finally, in determining additionality, we may worry that destroying these gases might cause similar chemicals to be produced to meet the demand for this type of gas, a phenomenon termed “leakage.” Since the production of these gases is banned in all countries under the Montreal Protocol, they cannot be reproduced, but they might be replaced with non-banned gases that also have warming effects when released into the atmosphere. This is not a problem with refrigerants captured from end-of-life appliances, but it could be an issue for stockpiled gases.

Total carbon footprint of gas removal

Finding and incinerating ODS can require travel and shipping, which in itself can lead to CO2 emissions. However, these life cycle emissions are generally taken into account by the offset certifier when calculating the total emissions reduced.


There is no other market for ODS destruction. Additionality is much more straightforward to establish for ODS projects as compared to other carbon offset sectors. Most countries do not have any regulations on the use and destruction of existing ODS, even if their production is banned under the Montreal Protocol. Moreover, as mentioned before, no market exists for the destruction of these gases apart from the carbon offset market, so ODS-destruction projects have to rely on offsets to survive.


When ODS are destroyed, their contributions to warming are permanently removed. Reversal is not a concern in ODS projects.


ODS projects do not generally offer any co-benefits, but preventing ODS from escaping into the atmosphere can help prevent damage to the ozone layer.

Assessment of ODS projects

We find ODS-destruction carbon offsets to be one of the more compelling types of carbon offsets available. We have only found one ODS offset that we recommend, which is provided by Tradewater.

This work is preliminary and subject to change. Questions and comments are welcome at givinggreen@idinsight.org.

[1] For instance, see appendix 8.A on page 731 of the Refer to the IPCC 2014 AR5 report here.