Carbon sequestration and carbon capture are processes to remove carbon dioxide (CO2) from the atmosphere and store it. This is exactly what plants do when they convert CO2 into other molecules like sugars and proteins. Carbon dioxide can also react with water and limestone (CaCO3) to form calcium bicarbonate (Ca(HCO3)2) in an inorganic example of natural carbon sequestration. Generally, though, this term is used today to refer to man-made processes for removing CO2 from the atmosphere or for capturing it before it gets released (like from power plants). A number of approaches to long-term carbon dioxide storage are being, or have been, tried, including pumping the gas deep underground into natural rock formations, scrubbing the CO2 out from flue gas by reacting it with bases, or transforming the CO2 into other useful molecules for making polymers, just to name a few.