Developments since 2005 in understanding potential environmental impacts of CO2 leakage from geological storage

•We review research since 2005 on potential impacts of leakage from CO2 storage.•We consider near surface onshore and offshore impacts and those on potable groundwaters.•Low level leakage through faults or wells is likely to be limited and recovery rapid.•Effects are reduced by mixing, dispersion and buffering.•Larger leaks are possible but less likely and should be easier to detect and remedy.