Oceans are the biggest source of carbon. If we are able to find ways of sequestering CO2 emitted in the deep ocean floor in some way, we get to use the coal without adding to the CO2 content of the atmosphere. Abandoned oil wells are also good for storing CO2 for a long time. And who knows, we may find some other ways of dealing with the CO2 sequestered in future. Geothermal research is definitely a good idea but every bit of research in dealing with climate change helps.