They convert CO2 to calcite: "[S]cientists at Lamont-Doherty Earth Observatory at Columbia University and other institutions have come up with a different way

They convert CO2 to calcite: "[S]cientists at Lamont-Doherty Earth Observatory at Columbia University and other institutions have come up with a different way to store CO2.... Their approach involves dissolving the gas with water and pumping the resulting mixture — soda water, essentially — down into certain kinds of rocks, where the CO2 reacts with the rock to form a mineral called calcite. By turning the gas into stone, scientists can lock it away permanently."