How much carbon can our sedimentary basin reserves absorb? (Photo by David McNew/Getty Images)
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Earth’s carbon storage capacity is an important variable in determining how much carbon dioxide, a greenhouse gas that causes warming, can be removed from the atmosphere and safely tucked away for long periods without leaking back. Among the different ways of removing carbon from the atmosphere — such as planting trees or geological storage — geological carbon storage in sedimentary basins, i.e., carbon stored under rock layers, has historically been considered a more durable method. For this reason, many scientific studies have attributed a significant share of carbon removal to this option, especially in scenarios of very high global warming due to burning fossil fuels. Such confidence in the critical role of carbon capture storage in future scenarios has driven investment projections in this niche space to be as much as USD 80 billion in 5 years.
This long-standing confidence is now being tested, as a new study published last week in Nature challenges the premise of geological carbon removal and poses serious implications for future investments in carbon capture and storage. Most importantly, it warns against overreliance on geological carbon storage as the main option for removing carbon dioxide.
Storage potential from this source, i.e., sedimentary basins or geological reservoirs, was previously assumed to be vast, in the range of 10,000–40,000 GtCO₂. But the new study, by scientists at the International Institute of Applied Systems Analysis, finds the estimates to be only around 1,460 GtCO₂ — an astonishingly low number. To calculate this number, the study applies a spatially explicit, risk-based approach to exclude higher-risk areas, such as those with high seismic activity or protected ecosystems.
What are the implications of this new study for climate science and finance? It raises two key considerations: For investors, it means balancing the carbon removal portfolio by looking at alternative carbon removal options beyond geological storage. And for policy officials, it means revisiting and adapting national mitigation plans in light of limited and uneven storage potential.
Consider Options In Carbon Storage, Including Alternatives Such As Marine Carbon Removal
The study’s most important point is the need for diverse durable carbon removal options. Marine-based carbon dioxide removal is one such alternative. Marine carbon removal can work in different ways, such as creating algae or changing the chemical composition of water to remove carbon dioxide or enhance its storage capacity.
Some of these methods have existed since the 1980s, so they are not entirely novel, but they require fresh attention based on the progress that has been made in the past few years, during which as many as 50 startups have come up in this space, according to Brad Ach, CEO Ocean Visions. This area is largely underfunded compared to investments in other methods of direct air capture and storage. Questions around scalability, economic feasibility, and potential negative impacts on local ecosystems may explain the gap, highlighting the need to build this trust through more investments in research and development.
The startup ecosystem in marine carbon removal, in particular, requires more support to de-risk early investments. Vycarb, for instance, has developed a carbon management technology with sensors that can check for optimal carbon content in water, monitoring bicarbonate levels they produce when CO₂ is stored in water bodies. Garrett Boudinot, CEO of Vycarb, highlighted the limits to how much can be converted to bicarbonate in one location. Their sensor helps to understand the optimal levels in real time, thereby ensuring carbon permanence and reducing adverse ecosystem impacts. Much of their work has been with independent parties to show that these chemical reactions permanently store CO2 and do not negatively affect ecosystems, drinking water, or seismic activity. Many investors are already actively supporting such startups, but there is great potential to scale up operations.
Account For The Geographical Variation in Geological Carbon Storage Potential
The new study also revealed that some regions of the world have better geological storage potential than others. Countries such as the US, Canada, Russia, and several Arab states are better placed to implement geological solutions, while Europe — a historically high emitter — has less storage potential.
Meanwhile, some developing countries that have historically been low emitters, such as Indonesia and Brazil, have robust storage potential. However, due to their low historical emissions share, these countries may have fewer incentives to invest in such expensive technologies. If captured carbon needs to be transported across regions on a large scale, this would involve significant costs and leakage risks. Another reason to explore alternative options for durable carbon removal.
This geographical variation also affects fairness and equity in national mitigation plans. Many mitigation plans, such as Nationally Determined Contributions, popularly called NDCs, assume that such carbon removal can offset all future residual emissions. However, given the uneven geological storage distribution, not all countries can rely on reservoirs equally.
Limited geological storage will also make early-stage decarbonization — notably phasing out fossil fuel sources — all the more critical and maybe even more cost-effective for some countries. This will reduce the need for future large-scale carbon removal in the first place.
The study is very timely as authors of the seventh assessment of IPCC begin to convene from this year. The findings will give the scientists reasons to reconsider future climate mitigation pathways in light of these limitations.
Geological carbon storage is not the silver bullet. While many alternatives, such as marine CDR, may not yet be as well developed, with the proper support to test and de-risk them, there is potential to tap into our vast ocean and water resources without adverse effects on nature. A portfolio approach to durable carbon removal — beyond just geological storage — is both a financial and policy imperative for climate action.
