Definitions and mechanisms for managing durability and reversals in standards and procurers of carbon dioxide removal

Carbon markets are expanding to include various forms of Carbon Dioxide Removal (CDR). Standards used in the certification of CDR must define the durability of removals and implement mechanisms to manage carbon that escapes from storage. These definitions and mechanisms will impact the ability of a global carbon management system to reach and maintain carbon neutrality targets in the long term. Collecting data from 28 international standard developing organizations (SDOs) and 268 proposals received by one large carbon removal purchaser, we reviewed the different definitions and mechanisms proposed to implement durability and manage carbon loss from storage. We find that standards most often use a stipulated contractual duration of storage of 100 years, but ranges from 10 to beyond 100 years. Project developers expect their storage to last between 1 year and 10 million years and most seem willing to provide a guarantee of storage duration. Six different mechanisms are used by SDOs to manage durability and four to manage carbon loss from storage during the contractual timeframe, but the rationale for a choice is not clearly associated with the CDR method, the stipulated duration, or the type of market. The most used mechanisms are commitment periods for durability, and buffer pools and required compensation for reversal management. Although it is an incomplete picture, this global system covers a wide range of durability and stipulated contractual durations; shows signs of common practices; shows a willingness to guarantee storage; has multiple mechanism options; and has no clear association between the choice of mechanism and the type of CDR method, stipulated duration, or type of market. Further work should focus on analyzing the trade-offs for each mechanism and informing the definition of permanent storage so a global carbon management system can develop to maintain carbon neutrality targets in the long term.