For decades, carbon capture and storage (CCS) has been touted as a linchpin of climate mitigation strategies, with theoretical global capacity estimates soaring as high as 40,000 gigatons of CO₂ (GtCO₂). But a rigorous, risk-based analysis published in Nature delivers a sobering reality check: Earth's prudent geologic storage potential is only about 1,460 GtCO₂ (with a range of 1,290–2,710 GtCO₂ considering uncertainties). This starkly lower figure—roughly an order of magnitude less than common industry and academic estimates—demands a fundamental rethink of climate pathways relying heavily on subsurface carbon sequestration.

Why the Massive Discrepancy? A Risk-First Assessment

The research team, led by Matthew Gidden from IIASA, moved beyond simplistic volumetric calculations. They applied a spatially explicit, precautionary framework evaluating seven critical risk dimensions across global sedimentary basins:

  1. Geophysical Hazards: Excluding basins near active seismic zones where injection could trigger earthquakes or fault reactivation, compromising seal integrity.
  2. Depth Constraints: Limiting injection to 1-2.5 km depths (onshore/offshore) to ensure supercritical CO₂ stability and minimize deep-fault risks.
  3. Human Proximity: Imposing 25km buffers around projected future high-population centers to mitigate risks from potential groundwater contamination or surface leakage.
  4. Environmental Protection: Excluding protected areas (IUCN categories) and polar regions (Arctic/Antarctic circles).
  5. Ocean Depth: Restricting offshore storage to waters ≤300m depth (aligning with 90% of current oil/gas infrastructure feasibility).
  6. Policy & Geopolitics: Accounting for current national CCS bans/restrictions and disputed maritime territories.
  7. Transboundary Issues: Applying buffers along international borders where shared basin governance is uncertain.

"Treating geologic carbon storage as a limited intergenerational resource has deep implications for national mitigation strategies. We must make explicit decisions on priorities for its use—abating unavoidable emissions or enabling durable carbon removal," the authors state, highlighting the core tension exposed by their findings.

Crunching the Climate Math: Implications for Net-Zero and Beyond

The study's implications are profound when benchmarked against IPCC climate scenarios:

  • Net-Zero Emissions: Most 1.5°C pathways stay within 50% of the 1,460 GtCO₂ limit by the time net-zero CO₂ is reached (typically ~2050-2055). However, maintaining the annual sequestration rates needed at net-zero (averaging ~8.7 GtCO₂/yr for 1.5°C pathways) would exhaust the prudent limit within ~150-250 years.
  • Temperature Reversal Cap: If the entire prudent storage capacity were used solely for Carbon Dioxide Removal (CDR) to draw down global temperatures, the maximum achievable cooling is capped at 0.7°C (0.35–1.2°C). Every ton used for fossil fuel CCS (e.g., blue hydrogen, cement/power plant capture) reduces this CDR potential.
  • Overshoot Danger: Scenarios allowing significant temperature overshoot beyond 1.5°C before attempting drawdown often require cumulative storage exceeding 2000 GtCO₂ by 2100. Over 50% of these scenarios breach the prudent planetary limit before 2100, particularly in Asia (including China and India), making a return to safer temperatures physically precarious or impossible.
  • Infrastructure Scale-Up: Achieving net-zero in 1.5°C scenarios requires a ~175-fold increase in annual CO₂ injection rates from today's levels—equivalent to current global crude oil production volumes. This presents monumental engineering and governance challenges not reflected in optimistic models.

The Geopolitics of a Scarce Resource

The analysis reveals stark inequalities in prudent storage distribution relative to historical responsibility and economic capacity (Fig. 4):

  • Storage-Rich & High-Responsibility: Countries like the US, Russia, and Canada possess significant resilient storage and high historical emissions.
  • Storage-Poor & High-Responsibility: The EU, Japan, and others have high emissions but limited domestic prudent storage, necessitating carbon exports.
  • Storage-Rich & Low-Responsibility: Nations like Brazil, Indonesia, and the DRC hold substantial storage potential but minimal historical emissions, raising equity questions about utilizing their subsurface 'space'.
  • Incumbent Advantage: Major fossil fuel producers (Saudi Arabia, UAE, Australia, Norway) retain robust storage potential, positioning them to pivot towards 'carbon sink' services—but requiring massive financial and policy shifts.

Beyond Sedimentary Basins: No Easy Fixes

The study focuses on sedimentary basins due to their maturity and current use. While basaltic mineralization (e.g., CarbFix in Iceland) offers a potential alternative, it remains technologically nascent and volumetrically unproven at climate-relevant scales. Governance challenges, public acceptance, and the sheer time/cost for basin characterization further constrain practical deployment speed.

A Call for Strategic Foresight

This research forces a paradigm shift: Geologic storage is a scarce intergenerational resource, not a limitless waste dump. Policymakers and technologists must prioritize its use with unprecedented rigor:

  1. Minimize Fossil CCS Dependence: Aggressively deploy renewables, electrification, efficiency, and demand reduction to avoid locking in fossil CCS for avoidable emissions.
  2. Reserve Storage for Hard-to-Abate Sectors & CDR: Prioritize storage for industries like cement, and crucially, for high-durability carbon removal to reverse overshoot.
  3. Develop Transparent International Frameworks: Establish equitable governance for shared basins and cross-border carbon transport/storage.
  4. Invest in Alternative Durability: Accelerate R&D for non-geologic durable storage (e.g., mineralization, carbon-negative materials) and improve land-based carbon management.

The era of assuming vast, cheap underground storage is over. Climate strategies must now operate within Earth's prudent planetary boundaries—or risk rendering temperature reversal impossible.

Source: Gidden, M.J., Joshi, S., Armitage, J.J. et al. A prudent planetary limit for geologic carbon storage. Nature (2025). https://doi.org/10.1038/s41586-025-09423-y