Carbon capture and storage is seen as one of the key techniques to help reduce the amount of carbon dioxide (CO₂) released into the atmosphere.
But new research suggests that the space available underground to safely store CO₂ could be much smaller than previously estimated.
Storing carbon underground has been presented as a key response to climate change by reducing the amount of CO₂ emitted into the atmosphere, and at some future point even reducing the amount of CO2 in the atmosphere to reverse some of the consequences of climate change.
At the moment the technology is only seeing limited deployment although this is expected to grow, in particular to reduce the carbon emissions from hard-to-decarbonise industries like steel and chemicals.
Now a report has mapped the areas that could be practically used for underground carbon storage, warning that this geological storage is a scarce, finite resource and must be used in a highly targeted way.
The paper, published in Nature, estimates a ‘prudent global limit’ of around 1,460 billion tons of CO₂ that can be safely stored in geologic formations. That amount, it said, is almost ten times smaller than estimates that have not considered risks to people and the environment.
The report’s 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, US aid the 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,” he said.
The team also looked at what these storage limits mean for the planet’s ability to cool down after overshooting temperature goals. They calculate that if the total available geological storage capacity was used for CO₂ removal - and no further emissions were produced beyond that point - a maximum 0.7°C warming reversal would be possible before available safe storage sites were filled. Other estimates have suggested much larger reversals in temperature of 5°C to 6°C
Report co-author Joeri Rogelj, Director of Research at the Grantham Institute and PM senior research scholar at IIASA said: “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 on-going and avoidable CO2 pollution from fossil electricity production or outdated combustion engines.
Fossil fuel producing countries such as the US, Russia, China, Brazil and Australia have the most potential safe storage as disused mines are the most efficient type of geological storage, the study noted. About 70% of all storage is onshore, with the remaining 30% at offshore sites.
The report shows that carbon capture and storage while a powerful tool in the fight against climate change, is not a bottomless solution, said Robert Sansom, a member of the Institute of Engineering Technology's (IET) Sustainability and Net Zero Policy Centre. “We should prioritise its use for long-term carbon removal, not just as a way to delay the transition away from fossil fuels. Engineers have a vital role to play in making sure storage sites are safe, effective, and used responsibly,” he said.
Carbon capture and storage can either decarbonise industrial processes or remove CO₂ from the atmosphere to reverse climate change, said Professor Carrie Lear, Professor of Past Climates and Earth System Change at Cardiff University’s School of Earth and Environmental Sciences.
“We’ve assumed we could do both, storing CO₂ underground where we have extracted fossil fuels. But this study challenges that assumption, showing that if we avoid risks to people and sensitive environments like the Arctic, the safe storage potential drops by a factor of ten. If future generations will depend on CCS to maintain net-zero emissions, then we must act now to preserve that option. That means cutting CO₂ emissions rapidly today. We cannot afford to use up this finite resource on short-term industrial fixes when its long-term value lies in restoring a safe climate,” she said.
Other researchers have noted that there are still other options for carbon storage to be explored, such as the storage resources of mineralisation by chemical reaction of CO2 with volcanic rocks or in basalt formations or directly in the ocean.
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