Carbon Storage’s Prudent Limit: The End Of Infinite Assumptions – CleanTechnica

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The publication of A prudent planetary limit for geologic carbon storage in Nature is an important moment in the conversation about carbon capture and storage. For decades storage has been discussed as if it were an almost limitless global sink, with estimates running from 10,000 to 40,000 gigatons of CO₂ in sedimentary basins alone. Industry reports spoke confidently of 14,000 gigatons of capacity. Policy models often assumed that storage was effectively infinite and treated it as a backstop for both prolonged fossil fuel combustion and for reversing overshoot scenarios later in the century. The new work cuts through that optimism by applying a risk-based filter to the entire map of global sedimentary basins. What emerges is a prudent planetary limit of about 1,460 gigatons of CO₂, or about 90% less than the technical figures that have dominated the discourse.

The methodology matters. Rather than counting pore space, the team layered in seismic risk, depth limits between 1 and 2.5 km, shallow water constraints of less than 300 m, 25 km buffers around projected urban areas, protected zones, polar circles, and contested maritime regions. The exercise moved CCS from the abstract world of geological potential to the real world of safety, environmental protection, governance, and public acceptance. It also revealed that only some countries retain significant safe storage potential after these exclusions are applied. The United States, Russia, Saudi Arabia, and Australia remain robust. Europe, India, Norway, and Canada see sharp reductions. That uneven distribution has clear equity and geopolitical implications.

This is where I need to offer a mea culpa. In earlier writing I argued that the main limits to storage were likely to come from reservoir collapse, injection pressure, and permeability constraints. I was focused on injectivity and geomechanics. Those concerns are real, but they represent only one slice of the risk picture. At the time I overstated them and did not account for the broader set of social, environmental, and governance filters that now define the prudent limit. The new paper has corrected the framing. It shows that while injectivity remains a rate constraint, the bigger story is that vast portions of the theoretical map are simply off limits if we take harm prevention and long-term safety seriously.

The implications are significant. At best the full prudent limit of 1,460 gigatons could deliver about 0.7 °C of cooling if every molecule stored were dedicated to durable removals. If instead storage is allocated to offsetting continued fossil fuel combustion, the amount of achievable cooling falls proportionally. Most 2 °C pathways already use up to 2,000 gigatons of storage this century, which overshoots the prudent ceiling. Even some of the 1.5 °C scenarios that rely heavily on removals exceed it. This means that CCS cannot be both the lifeline for fossil fuels and the safety valve for overshoot. Only rapid reductions in gross emissions can keep climate stabilization within reach without blowing through the safe storage budget.

This finding is consistent with arguments I have made for years about the role of CCS. It should not be built out as a general-purpose rescue plan for coal and gas. It should be reserved for the hardest to abate industrial point sources such as cement kilns and some steel production. It may also play a role in dedicated negative emissions pathways, but only when the CO₂ stream is relatively pure and cheap to capture, such as from biogenic fermentation. A merit order for scarce storage capacity emerges naturally. First use biogenic CO₂ that is already concentrated, then residual industrial emissions that have no substitute, and finally small amounts of direct air capture where energy is abundant. Using storage to extend fossil combustion is the lowest priority and makes no sense when every gigaton stored reduces the cooling potential available to future generations.

Transport and safety risks reinforce this hierarchy. The paper’s 25 km urban buffer is an acknowledgment of the hazards associated with dense pipeline networks in populated regions. This is something I have highlighted in the past. A Europe-wide or North American CO₂ transport system would run through heavily settled areas, raising rare but high consequence risks. Routing, detection, and emergency response costs climb steeply under those conditions. That is another reason why storage should be allocated sparingly and to the most valuable climate uses. The lessons of what CO₂ pipelines might mean were highlighted by Satartia, Mississipi’s pipeline rupture. The tiny town of 46, 1.6 km from the pipeline in a very sparsely populated region, saw dozens unconscious and hospitalized and a couple of hundred evacuated.

Costs tell the same story. Real projects such as cement CCS in Norway are already delivering capture costs in the range of €120 to €150 per ton, with significant capital intensity, as I noted in my assessment of the Northern Lights CCS program. Comparing those numbers to renewables and electrification shows why CCS is unlikely to win outside of narrow niches. The new study does not quantify costs, but its risk framing implies the same conclusion. The cheap, easy volumes vanish when real constraints are applied. The remaining capacity is a scarce and expensive commons.

The equity dimension is important. Regions with robust storage potential after risk screening may find themselves offering storage as a service to others. That raises questions of distributive justice, liability, and fairness. Countries like Indonesia and Brazil may have strong storage potential but little historic responsibility for emissions, which complicates incentives. Europe, with high historic emissions but weak remaining storage, will need to import storage or lean harder on alternatives. These dynamics underscore the need for global agreements that treat storage as a limited intergenerational resource rather than a private commodity.

The authors of the Nature study focused only on sedimentary basins because that is where almost all planned CCS projects exist today. They explicitly excluded other sequestration pathways such as mineralization in basalt, carbonation of ultramafic rocks, and injection into industrial waste streams or mine tailings. I think this was a very reasonable choice. These methods remain at pilot scale, with highly uncertain scalability and little real-world data, even if their long-term potential could be significant. It makes sense to establish a prudent limit based on what is mature enough to matter in the coming decades rather than dilute the analysis with speculative options. I have written recently about ClimeWorks’ mineralization failure and the state of direct air capture, and the same principle applies there. Technology that is still in its infancy should be recognized for its promise, but not assumed as a dependable pillar of climate planning until it demonstrates scale, durability, and cost effectiveness. Pragmatic skepticism is required.

All of this reframes climate pathways. Overshoot strategies that rely on gigaton-scale storage for centuries are not credible under the prudent limit. Net zero by mid-century followed by rapid drawdown remains possible, but only if storage is carefully rationed. This strengthens the case for front-loading emissions reductions and accelerating electrification. It also elevates the importance of other carbon sinks, such as long-lived biogenic products like mass timber, soil carbon improvements, and forest conservation. These reduce dependence on the finite subsurface budget.

The lesson is clear. Storage is not limitless. It is finite, risky, and unevenly distributed. Policymakers should treat it as a budget to be managed, not a get-out-of-jail card. My own earlier work overstated one set of geophysical constraints but underplayed the broader picture. The new research corrects that. It gives us a clearer sense of what storage can do and what it cannot. The future of climate stabilization depends on recognizing those limits and making the hard choices about how to allocate this scarce global commons.