The Scenario Bias Understates Earth’s Captured Co2 Injection Capacity
A review of the Associated Press story, Study: Less carbon storage capacity than thought, by Tammy Webber, based on Gidden et al., A prudent planetary limit for geologic carbon storage, Nature, September 3, 2025.
Associated Press, September 3, 2025 – “The world has far fewer places to securely store carbon dioxide deep underground than previously thought, steeply lowering its potential to help stem global warming, according to a new study that challenges long-held industry claims about the practice…”
REVIEW: The Title and Content of this AP Article is Misleading – Why? The Scenario Bias.
Bruce Melton PE
Director, Climate Change Now Initiative
The Associated Press Article by Tammy Webber is based on the findings: Gidden et al., A prudent planetary limit for geologic carbon storage, Nature, September 3, 2025.
https://www.nature.com/articles/s41586-025-09423-y#Sec9
This study’s findings are accurate, at least mostly, but the choices they made in the scenarios they evaluated do not reflect the reality of plausible and feasible carbon capture quantities as they exist. It has to be; one cannot study everything related to a hypothesis, therefore scenarios must be chosen to evaluate. This is one of the major challenges of science. Scientific evaluation is scenario based. Issues not included in the scenarios evaluated are simply not evaluated. This is called the “scenario bias,” and it is ever present in almost all scientific research. Reporting of scientific findings by popular literature as being definitive is a huge problem, that does not take this “scenario bias” into consideration and as is the case with this reporting by the Associated Press, the title of this article and the things it reports from the academic research are not valid when scenarios other than those considered are evaluated.
What Gidden 2025 says, with all of their scenario-based caveats, is that it appears that at worst, the findings in this report are not even an absolute minimum floor for global sequestration capacity with 1.5 or 2 C best-case warming scenarios. These caveats of Gidden 2025 are described below:
This evaluation only looks at sedimentary geology, and includes no ultramafics, or basalts like with the Orca project https://climeworks.com/plant-orca by Climeworks in Iceland, where ultramafic rocks have a plausible sequestration capacity ten times that of sedimentary geology.
The authors limit storage between 1 and 3 km deep as a conservative approach to limiting minor seismic activity and surface leakage, where current regulatory requirements for oil industry drilling waste and CO2 injection are based on safe geologic practices with no depth limit, and typical minimum depth based on science is 800 meters.
They limit subsea disposal to less than 300 m below the ocean surface, where floating platforms can operate in depths over a mile. The Deep Water Horizon was in 5,000 feet and large platforms can have over 8o directional bores each.
The 3 km maximum depth for minor offshore seismic activity is moot because of impacts from minor seismic activity and, offshore leakage of even the biggest leaks is absorbed in just a few to several hundred feet of water.
Their analysis is heavy on carbon capture and sequestration (CCS) scenarios from emissions of fossil fuel energy generation and industry, which have a 50 percent removal penalty versus atmospheric capture, and their maximum rate is only 15 Gt (gigaton) CO2 storage by 2100 as per standard Intergovernmental Panel on Climate Change (IPCC) scenarios. The removal penalty is that half of greenhouse gases emitted by humans are absorbed by natural systems like forests and oceans, where if the carbon is captured from the atmosphere instead of at the point of exhaust emissions, this natural absorption can be leveraged to reduce the atmospheric removal amount by half. The 15 Gt C2 storage estimate is for best case scenarios that run to the year 2100 and a warming target of 1.5 degrees C above normal where right now, most Earth systems are degrading and beginning to emit, not store carbon. And, if the warming that caused the degradation to begin is not removed promptly, these systems (forests, oceans, soils, permafrost, etc.) do not self-restore. In other words, now that degradation has begun, collapse of these systems is baked in and foregone, unless we cool our climate back to the evolutionary boundaries of these systems where they are stable and not degrading. The tipping point, or the point of no return threshold where these systems become so degraded they cannot self-restore even if the warming that caused their degradation is removed, is about 1 degree C warming above normal (where current warming is about 1.5 degrees C above normal) and importantly, If our climate is not restored by about mid-century, it is foregone that these systems will be so degraded they cannot self-restore.
Time frames are then extremely important to the amount of carbon that needs to be removed from our atmosphere to keep our degraded Earth systems from collapsing. The scientific literature suggests the time frames to prevent irreversible collapse (tipping) for most already degrading systems is about mid-century. Right now many Earth systems are emitting and not storing because of already occurred degradation. As degradation continues, emissions increase nonlinearly over time and they are substantial, plausibly exceeding human emissions in just decades, far more than doubling carbon capture and sequestration capture requirements. Therefore time is of the essence. This report does not consider tipping in its caveats where they follow IPCC scenarios.