Different types of carbon dioxide removal (CDR) differ greatly in the extent to which they are permanent. The risk of reversal is always present for land-based sinks and other types of removal based on short duration carbon cycles. In contrast, removals to geological storage are largely permanent. This Policy Brief paper explores three broad approaches to recognising and managing these differences in the context of the certification of carbon removal.

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It is essential for good climate policy that the different risks of reversals for different types of carbon dioxide removal are recognised, and that policy takes account of them. This briefing outlines three possible approaches for a certification system for removals to manage these risks. Much more work is needed to develop them further: none of the approaches are perfect, nor are they mutually exclusive. Reliable and robust monitoring, reporting and verification mechanisms are essential for certifying removals.

A hybrid of all three approaches is likely to be required for the system to be effective. Since the value of removals in limiting climate change is dependent on the permanence of the carbon storage, any certification of removals must recognise the fact that a reversal of carbon storage also results in a reversal of the value of a removal certificate unless robust measures are in place to account for and manage reversals. Concurrently, if an emission has been offset with a certificate which is later nullified, that emission should be liable to pay the current carbon price.

Approach 1 keeps the long and short carbon cycles separate and eliminates the fungibility between the various carbon sinks. This approach could underpin the entire governance framework for CDR.

Approach 2 adjusts the upfront value of a carbon removal certificate to the estimated risk of reversal. A CDR method which is more likely to be reversed therefore produces a certificate which is less valuable than a certificate produced by a CDR method which is less likely to reverse. This approach is not viable for CDR methods which are highly reversible.

Approach 3 ties a perpetual liability to a CDR certificate, whereby any reversal must be replaced for the certificate to retain its value. Every time the CO2 storage is reversed, more CO2 must be removed to make good on the reversal.