Energy Transition Commentary:
A recent article in Nature by Gidden et al [1] claims to establish ‘a prudent planetary limit of 1,260 – 2,710 Gt of safe CO2 geologic storage’ which an associated press release claimed has great policy and practical implications because it is almost ten times smaller than previous estimates. This study should be viewed with caution as it is based on a simplistic methodology which does not make use of far more detailed data and analyses of regional geological systems included in established methods. By a subjective filtering process they have managed to produce a model that has reduced available storage resources from one very large number to another very large, albeit lower, number. Moreover, since most Integrated Assessment Models (IAMs) for the energy transition to net-zero agree that the CCS contribution to achieving net-zero needs to be ~10 Gtpa, even this new likely underestimate of storage capacity represents ~125- 270 years of storage, which is more than enough to enable the transition to other long-term decarbonisation solutions.
Neither the IAM modellers nor the industry/policy proponents of CCS claim that CCS is required to achieve all the decarbonisation required to achieve net-zero, simply that it is an essential part of the technology jigsaw, removing 10-20% of the CO2 which would be emitted if we continued on a business-as-usual trajectory. So the alarmist comments in the press release that this new study should be considered a gamechanger for carbon storage, because it cannot achieve a 6oC reduction in global temperature rises, are unfounded; CCS is not considered to be ‘an unlimited solution to bring our climate back to a safe level’ in any viable transition scenario and its required contribution to reducing mean global temperature rises is less than the 0.7oC which Gidden et al project is the maximum possible in their ‘prudent’ model.
So where are the flaws in this new study of CO2 geologic storage capacity? The authors suggest that they have identified that the prudent resource base for CO2 storage globally is far lower than previously estimated because past efforts, largely led by geological surveys and national laboratories (misleadingly referred to as industry estimates in the paper), have not considered important physical and socio-political risks. What the authors fail to acknowledge is that the physical limitations that comprise the vast majority of their reductions (ocean depth, sedimentary depth, locations in polar circles) are already incorporated into past assessments.
Thus, rather than having identified important considerations that were previously ignored, it is apparent that the authors have simply implemented a geological modelling approach that is pre-disposed to estimate the resource base for CO2 storage far below estimates arising from established standards developed over the past 20 years. When a similar approach was taken in Wei et al., 2021 [2] a similar result was obtained. Whether this systematic bias arises from some fundamental error in the approach can only be assessed once the full dataset can be scrutinised, but it is notable that established methods make use of far more detailed data and analyses of regional geological systems than was used in this work.
It is a shortcoming of this work that the authors do not validate their modelling approach, or explain major and systematic differences as compared with alternative and established methods. The bias in the estimates would have been revealed immediately by comparison of the authors’ estimates to any number of detailed regional analyses that have been carried out, for example, in the United Kingdom, Norway, and the United States. Indeed it can be seen in the open peer review documentation that this and many of the issues above were pointed out by the reviewers, but not addressed in the rebuttals.
In short, irrespective of the caution that should be given to this lower estimate of global CO2 storage capacity, the extent to which CCS is required to contribute to climate change mitigation through power and industrial decarbonisation will not be limited by the amount of viable, safe storage capacity. Ultimately, whether it is 1,200 Gt, 2,000 Gt, or 10,000 Gt, there is far more potential storage resource than is needed for CO2 storage to play a major role (~20%) in emissions mitigation. Approaching even 1,000 Gt of CO2 stored underground would be a signal achievement in our fight against climate change. Thus even if 200 years from now we are needing to find alternatives to the use of CO2 storage for want of geology, this will be a problem that we can welcome and for which ample solutions should be in place and routine practice by then. However, we need to get through the next 25-50 years first; it is its speed of implementation at scale using the available storage capacity that will be the limiting factor in how successful CCS will be in contributing to achieving net-zero quickly enough.
[1] Gidden, M.J., Joshi, S., Armitage, J.J. et al. A prudent planetary limit for geologic carbon storage. Nature 645, 124–132 (2025). https://doi.org/10.1038/s41586-025-09423-y
[2] Wei, Y. M., Kang, J. N., Liu, L. C., Li, Q., Wang, P. T., Hou, J. J., … & Yu, B. (2021). A proposed global layout of carbon capture and storage in line with a 2 C climate target. Nature Climate Change, 11(2), 112-118. https://www.nature.com/articles/s41558-020-00960-0
Professor Martin Blunt, Professor of Flow in Porous Media
Professor Paul Fennell, Professor of Clean Energy
Professor Sam Krevor, Professor of Subsurface Carbon Storage
Professor Niall Mac Dowell, Professor of Energy Systems Engineering
Professor Geoffrey Maitland, Professor of Energy Engineering
Professor Ronny Pini, Professor of Multiphase Systems
Professor Martin Trusler, Professor of Thermophysics
Imperial College London, Transition to Net Zero Group