Two US studies have raised questions over the risks of storing carbon emissions underground, linking the practice with an increased risk of earthquakes.

Carbon capture and storage (CCS) is considered a viable strategy for pollution control and a method for reducing carbon emissions by the United Nations Intergovernmental Panel on Climate Change.

The technique works by capturing, liquefying and injecting carbon emissions underground at high volumes. However, no large-scale carbon capture projects of this nature are yet under way.

A study by Stanford University in California suggests that storing huge volumes of fluid underground for long periods could create seismic instability.

“There is a high probability that earthquakes will be triggered by injection of large volumes of carbon dioxide into the brittle rocks commonly found in continental interiors,” say the study’s authors, geophysics and environmental earth system science professors Mark Zobacka and Steven Gorelick.

This view is supported by a study by the US National Research Council, commissioned by the Department of Energy, which concludes that “CCS, due to the large net volumes of injected fluids, may have potential for inducing larger seismic events”.

The National Research Council also studied the links between seismic activity and other types of underground fluid injection and withdrawal activities such as the extraction of coal seam gas and disposal of wastewater.

It found that hydrofracking for coal seam gas “does not pose a high risk for inducing felt seismic events”, but concluded that the injection of wastewater resulting from energy exploration into the ground “does pose some risk for induced seismic activity”.

But the study noted that “very few” seismic events relating to the injection of wastewater have been documented relative to the number of disposal wells in operation in the US over the past decade.