Carbon storage: keeping a lid on it

Controlling climate change by long-term storage of atmospheric carbon dioxide will require keeping an extremely tight lid on the sequestered reserves. So says Gary Shaffer, a geophysicist based in Copenhagen who has modelled climate impacts based on a range of carbon leakage scenarios.

Carbon Capture and Storage (CCS)

Carbon sequestration is being promoted by some as a viable tool for dealing with climate change through the offsetting of carbon emissions from power stations and other combustion sites. The European Union, for example, plans to invest billions of euros over the coming decade to develop carbon capture and storage technologies. CCS has many critics, however, and to date little practical progress has been made.

Pump carbon dioxide underground or into the sea bed, and there is a risk that over time it will leak out. It all depends on the geology of the storage site, and in some cases this is little understood. But the risk is quantifiable, and Shaffer’s work on carbon leakage is a significant contribution to such an environmental risk assessment. In his study, Shaffer used a model developed at the Danish Center for Earth System Science to project climate impacts over the next 100,000 years. He compared a diverse range of carbon sequestration scenarios, including one for deep-ocean disposal and four for underground storage, and two projections of climate change with no sequestration: one with high carbon emissions and one with low emissions.

“CCS has many potential advantages over other forms of climate geoengineering,” says Shaffer. “It makes good sense to modify the Earth’s radiation balance by putting carbon back in where it came from rather than to mess around with short-lived aerosols. Atmospheric CO2 is long-lived and evenly-distributed globally making it possible to manage it in a long-term, controlled way with less chance for unpleasant climate surprises. However, potential short and long-term problems with leakage from underground storage should not be taken lightly. Carbon in light form will seek its way out of the ground or seabed. The present situation in the Gulf of Mexico is a poignant reminder of that fact.”

In a paper published recently in Nature Geoscience, Shaffer shows that where carbon leakage exceeds 1% per thousand years, a large, delayed global warming will occur, along with oxygen depletion and ocean acidification. Limiting carbon leakage to less than 1% is a pretty tall order, given the uncertainties involved in such planetary-scale engineering. If the limit is breached, leaked carbon would have to be re-sequestered continuously over thousands of years in order to keep things in check. That seems like rather a large burden to impose on future generations.

Further reading: Gary Shaffer, “Long-term effectiveness and consequences of carbon dioxide sequestration”, Nature Geoscience 3, 464 (2010)