I looked relatively deeply in to this area when starting an asset exchange ~2011. My conclusion at that time was that existing carbon trading / offsets tokens were basically non-fungible due to disparate definitions from different regulators. Nominal assets ranged from honor-system self-declarations to heavily audited. The resulting asset types were found to be effectively illiquid, despite a rush to open exchange platforms and media talk of trading schemes, owing to lack of buy-side demand. Individually the systems were mostly only useful for gaming local regulators. I doubt their primary purpose today has changed from multinationals greenwashing their dirty operations with suitably distracting levels of misdirection.