Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate

An issue of permanence: Assessing the effectiveness of ocean carbon sequestration

Howard Herzog, Ken Caldeira & John Reilly

Although it would seem that CO2 leakage after sequestration would only be a problem in a badly sealed reservoir, in actuality it is an issue for any form of sequestration technique. This paper investigates the benefits of such temporary storage.

Herzog, H., K. Caldeira, and J. Reilly. An issue of permanence: Assessing the effectiveness of ocean carbon sequestration, Climatic Change 59, 293–310, 2003.

Effectiveness of temporary storage compared to permanent storage: The percent effectiveness of temporary carbon sequestration in the ocean was calculated using three different cases. In case 1, the price of carbon leakage remained constant. In case 2, the price rose exponentially. In case 3, the price rose for a while before eventually leveling out. The various forms of case three involve different points at which stability is reached: 20, 500, 100, 200, and 500 years. Temporary sequestration ranges from useless (case 2) to effectively the same as permanent storage (case 1, as well as various cases at 3000m depth).


In this paper, we present a method to quantify the effectiveness of carbon mitigation options taking into account the “permanence” of the emissions reduction. While the issue of permanence is most commonly associated with a “leaky” carbon sequestration reservoir, we argue that this is an issue that applies to just about all carbon mitigation options. The appropriate formulation of this problem is to ask ‘what is the value of temporary storage?’ Valuing temporary storage can be represented as a familiar economic problem, with explicitly stated assumptions about carbon prices and the discount rate. To illustrate the methodology, we calculate the sequestration effectiveness for injecting CO2 at various depths in the ocean. Analysis is performed for three limiting carbon price assumptions: constant carbon prices (assumes constant marginal damages), carbon prices rise at the discount rate (assumes efficient allocation of a cumulative emissions cap without a backstop technology), and carbon prices first rise at the discount rate but become constant after a given time (assumes introduction of a backstop technology). Our results show that the value of relatively deep ocean carbon sequestration can be nearly equivalent to permanent sequestration if marginal damages (i.e., carbon prices) remain constant or if there is a backstop technology that caps the abatement cost in the not too distant future. On the other hand, if climate damages are such as to require a fixed cumulative emissions limit and there is no backstop, then a storage option with even very slow leakage has limited value relative to a permanent storage option.