The risks associated with the transport and injection of carbon dioxide are reasonably well understood and already borne in the USA. There is a remote possibility that CO2 disposed of underground could leak from a storage reservoir, either through an unidentified migration pathway or as the result of a well failure. The kind of threat that this might represent may be judged by comparison with naturally occurring volcanic CO2 emissions. Diffuse CO2 emissions through the soil or via carbonated springs in volcanic areas do not appear to represent a threat as long as the CO2 is able to disperse into the atmosphere. However, when CO2 is able to build up in enclosed spaces it poses a definite threat. Large CO2 clouds associated with sudden emissions from volcanic vents or craters also pose a lethal threat. However, there appears to be little analogy between such events and any possible leak from a storage reservoir via a natural unidentified migration pathway. Modelling of the development, migration and subsequent dispersal of any CO2 cloud which might arise from a well failure is recommended. doi:10.1016/S0196-8904(96)00276-2. http://www.sciencedirect.com/science/article/pii/S0196890496002762.
