Â鶹ÒùÔº

For the first time, a study maps safe areas that can practically be used for underground carbon storage, and estimates that using them all would only cut warming by 0.7°C. The result is almost ten times lower than previous estimates of around 6°C, which considered the total global potential for geological storage, including in risky zones, where storing carbon could trigger earthquakes and contaminate drinking water supplies. The researchers say the study shows that geological storage is a scarce, finite resource, and warn that countries must use it in a highly targeted way.

Storing carbon deep underground has been presented as an almost limitless solution to the climate crisis. The study led by IIASA researchers, in collaboration with an international team of colleagues, and in Nature, shows that the reality is far more limited than previously thought. The team has estimated a prudent global limit of around 1,460 billion tons of carbon dioxide (CO₂) that can be safely stored in geologic formations—an amount almost ten times smaller than estimates proposed by industry that have not considered risks to people and the environment.

Carbon storage is widely seen as essential for achieving climate goals, whether by capturing emissions from factories and power plants or removing COâ‚‚ from the atmosphere. According to lead author Matthew Gidden, a senior researcher in the IIASA Energy, Climate, and Environment Program and at the Center for Global Sustainability at the University of Maryland, U.S., the study's findings highlight the need for caution:

"With this study, we can conclude that carbon storage should be treated as an exhaustible, intergenerational resource, requiring responsible management. Hard choices must be made about which countries, which sectors, and even which generations are able to utilize it. It's critical that countries make clear in their climate action plans how they plan to use carbon storage in order to collectively achieve long-term climate goals while minimizing harm to human health, biodiversity, and sustainable development."

The researchers first analyzed total global geological storage by mapping sedimentary basins—underground rock formations where layers of sand, mud, and other materials have built up over millions of years. These basins are prime locations for both fossil fuel deposits and potential carbon storage.

The team assessed their suitability for carbon storage by considering risks such as COâ‚‚ leaking back into the atmosphere, the possibility of triggering earthquakes during the storage process, contamination of groundwater supplies, and proximity to population centers or protected areas. Sites that were too close to the surface to store carbon reliably, too far underground, or at ocean depths that make storage too expensive and risky, were also ruled out.

When these factors are taken into account, the global storage capacity shrinks dramatically from industry estimates of around .

The team also examined what these storage limits mean for the planet's ability to cool down after overshooting temperature goals, finding that if the total available geological storage capacity would be exclusively used for CO₂ removal and no further emissions would be produced by other activities at that point, a maximum 0.7°C warming reversal would be possible before available safe storage sites would be exhausted.

Larger engineering and industry estimates have suggested much deeper temperature drawdowns of 5°C to 6°C—and even higher in some studies—but those assessments failed to factor in risks to people and the environment and allow for much more extensive and riskier storage potential.

The authors emphasize that such comparisons highlight the stark difference between what is technically possible and what can be safely achieved. They also caution that removing carbon may not reduce warming in the same way that emitting it causes warming, and that the climate system might not return to its earlier state even if global temperatures are brought back down.

"This study should be a game-changer for carbon storage. It can no longer be considered an unlimited solution to bring our climate back to a safe level. Instead, geological storage space needs to be thought of as a scarce resource that should be managed responsibly to allow a safe climate future for humanity. It should be used to halt and reverse global warming and not be wasted on offsetting ongoing and avoidable CO₂ pollution from fossil electricity production or outdated combustion engines," explains co-author Joeri Rogelj, Director of Research at the Grantham Institute and PM senior research scholar at IIASA.

Fossil fuel-producing countries such as the United States, Russia, China, Brazil and Australia have the most potential safe storage, as disused mines are the most efficient type of geological storage. The countries with the lowest risks include Saudi Arabia, the Democratic Republic of the Congo and Kazakhstan, while countries that see large decreases in potential storage space due to high risks include India, Norway, Canada and countries in the European Union. About 70% of all storage is onshore, with the remaining 30% at offshore sites.

"There are still many unknowns around geological carbon storage. The technology has been around for close to 30 years, but it still hasn't been scaled to the levels needed to bring warming down. Identifying storage sites is a laborious process that needs to characterize very local geological properties to understand how much storage is actually possible. Previous research identified sites that can carry serious risks to humans and the environment and make rosy assumptions about how much carbon can be stored there. Our study asks and answers the opposite question: How much of the storage is actually safe and realistic to use?" Gidden says.

The team's work also highlights questions of fairness and responsibility. Countries with the largest fossil fuel industries often have the greatest storage potential, but also bear the greatest historical responsibility for emissions.

"This is not just a technical issue. it is about justice across generations and across nations. Countries that have historically contributed the most to emissions also have the most practical storage space available and must show leadership in using this resource responsibly. Decisions today will determine whether storage is used wisely or wasted," notes co-author Siddharth Joshi, research scholar in the Integrated Assessment and Climate Change Research Group at IIASA.

By showing that carbon storage is a finite global resource, the study calls for international cooperation and careful planning. The authors identify that some scenarios used to guide policymaking assessed by the IPCC would breach this global limit before 2100, and project that almost all scenarios would do so by 2200, highlighting the difficult tradeoffs facing energy and climate planners. Policymakers will need to decide how to balance the competing demands of ongoing fossil fuel use with the need to remove carbon from the atmosphere to protect future generations.

"Carbon storage is often portrayed as a way out of the climate crisis. Our findings make clear that it is a limited tool. With current trends suggesting warming up to 3°C this century, using all of the safe geological storage wouldn't even get us back to 2°C. Our study is a call for nations serious about meeting the Paris Agreement—they need to be clear, prudent, and practical about how they plan to use carbon storage to do so.

"Used strategically in conjunction with fast and deep emissions reductions, it will help us meet climate goals. But used carelessly while allowing fossil fuels to continue to proliferate, it could close off options for future generations," says Gidden.

The authors highlight that while carbon storage remains an important part of climate solutions, it should be treated like any scarce resource—with transparency, fairness, and a long-term vision.

The team has developed an that allows policymakers, researchers, and the public to explore the findings in detail. The platform provides country-level visualizations of safe, practical carbon storage potential, helping users understand the tradeoffs and risks involved in different regions. This tool is designed to support evidence-based decision-making and international cooperation on the prudent use of geological storage.