Earth’s capacity to store carbon could max out surprisingly soon

The planet’s capacity to store carbon-dioxide emissions in rock formations is much smaller than previous estimates suggest and it could run out as early as 2200, according to a study¹ published in Nature today.

To meet the goal of the 2015 Paris agreement — limiting global warming to 1.5–2 °C above pre-industrial temperatures — vast amounts of CO₂ will need to be removed from the atmosphere. One way to do that is to capture CO₂ produced by industry and store it deep underground.

Researchers report that Earth can safely store around 1,460 gigatonnes of carbon dioxide (GtCO₂) — a number much lower than the 10,000–40,000 GtCO₂ often cited in previous studies².

At present, carbon capture and storage technologies remove only 49 million tonnes of CO₂ annually, with a further 416 million tonnes per year in planned capacity, say the authors of the study. But to stay within the Paris target, annual carbon storage would need to rise to 8.7 GtCO₂ by mid-century — a 175-fold increase over the next three decades.

Low-risk storage

To estimate Earth’s storage capacity, the study — led by scientists at the International Institute for Applied Systems Analysis in Laxenburg, Austria — calculated that the planet has a physical storage reserve of 11,800 GtCO₂. But, when the researchers estimated how much of those reserves can be used practically without the risk of carbon leakage triggered by earthquakes, or without access being blocked owing to political decisions, the capacity dropped to 1,460 GtCO₂.

The study focused on the storage capacity of stable sedimentary basins, in which most prospective CO₂ storage sites are being considered.

Even if the 1,460 GtCO₂ capacity was used exclusively for removing carbon from the atmosphere, the effort would reverse global warming by only 0.7 °C. Current trends suggest that global warming will increase by up to 3 °C this century, even if all the identified geological storage for reversing climate change is used, it would not reverse warming back to 2 °C, says Joeri Rogelj, a co-author of the study and climate scientist at Imperial College London.

The researchers suggest that if stored CO₂ escapes to the surface, it could lead to the formation of carbonic acid in groundwater. Acidic conditions can dissolve metal-containing minerals, releasing toxic metals, which could harm humans and the environment.

Winners and losers