The Japanese National Maritime Research Institute has proposed a new technique to sequester CO2. The concept is to liquify the gas captured from the smokestacks of power plants. It would then be transported by tanker to an offshore location at least 2,700 meters deep. Here, the liquid CO2 would be compressed into a slurry (liquid/solid 50/50) and released through an injection pipe to a depth of about 500 meters. At that depth, it would be sufficiently dense to sink to the bottom and remain there for centuries.
Chemical Engineering magazine reports
"Because of the high pressure and the low temperature at such depths, a membrane of CO2 hydrate forms at the interface between the liquid CO2 and the seawater, which is expected to prevent the CO2 from being dispersed. A 1-to-80 model of the platform and injection system has been constructed, and the group plans to test the entire concept in the future."
If it works, there would be a sufficiently large dump in the oceans to sequester our CO2 output. The question is, would anyone want to pay the costs in parasitic energy losses (collection, liquification, transport and compression) to achieve the sequestration? It will cost much more than Al Gore's carbon offsets plan to accomplish. But it would be a viable way to actually deal with the accumulation of anthropomophic CO2 in the atmosphere.