A method for disposing of carbon dioxide is provided. According to the invention, CO.sub.2 is dissolved in seawater and the salinity of the seawater is increased to produce CO.sub.2-containing brine. The CO.sub.2-containing brine is denser than the seawater from which it is made. Therefore, when it is released into the ocean, the CO.sub.2-containing brine sinks to depth and sequesters the carbon dioxide. The brine may be produced by forming CO.sub.2 hydrate, which extracts fresh water from the seawater. Alternatively, the brine may be produced by forming water ice from the seawater and injecting CO.sub.2 into the seawater either before or, more preferably, after the water ice has been formed.