Rocks’ carbon storage capacity vastly overestimated: study

Many scientists and policymakers are counting on storing CO₂ deep underground as an important way to fight climate change. Such known as geological carbon storage involves capturing CO₂ from sources like power plants or directly from the air and injecting it into rock formations, where it can remain for centuries. However, so far, most discussions have treated underground storage as if it were limitless.

A new study in Nature has challenged this assumption, warning that the earth can only safely hold about 1,460 billion tonnes of CO₂ underground. If countries design climate strategies without knowing how much storage is really available, they may rely too heavily on an option that can’t deliver. Setting a limit forces governments to plan more carefully, reduce emissions faster, and carbon storage as a scarce resource, and acknowledge the need for a more realistic response.

To calculate this limit, the researchers, from Europe, the UK, and the US, built a global map of sedimentary basins, which are large rock formations most suitable for CO₂ storage. Then they systematically ruled out areas where storage would be too risky, e.g. basins near earthquake zones, in polar regions, and in biodiversity hotspots. Finally, the team considered practical constraints like storage depth and offshore drilling limits. By adding up what remained, they found that only a tenth of the previously estimated global capacity, of around 11,800 billion tonnes, was suitable.

Nearly every climate scenario that aims to keep global warming below 2º C assumes large amounts of CO₂ will be stored underground. But at today’s pace, storage use would grow so rapidly that this new planetary limit could be crossed by 2200. The study also showed that countries don’t share this capacity equally: it’s higher in Russia, the US, and Saudi Arabia and lower in India and many European countries.

The study also capped the maximum possible temperature reversal through storage to about 0.7º C, meaning underground storage alone can’t fix global warming. Second, treating storage as a finite resource raises questions about whether it should be used to keep burning fossil fuels a little longer or to remove carbon from the air to benefit future generations. Finally, the study is clear that emission cuts remain the most viable way forward. Carbon storage may help but it won’t replace faster transitions to renewable energy, changes in industry, and conservation of natural carbon sinks.

A press note issued by Nature clarified: “The authors note that a key limitation of this analysis is not accounting for the obstacles of scaling up carbon capture and storage technology or considering any other technologies that might be developed in the future.”