There were a few interesting talks at the American Geophysical Union meeting on geoengineering. Personally, I can't really figure out how mucking with natural systems, which got us into the global change conundrum we are now in, can still be seen as a viable approach, Aren't there likely to be further unknown and unforeseen consequences?
Stanford geophysicist Mark Zoback discussed the possibility of carbon sequestration causing small and moderate earthquakes. "While those earthquakes are unlikely to be big enough to hurt people or property, they could still cause serious problems for the reservoirs containing the gas. ... When we start perturbing the system by changing fluid pressure [as we inject massive amounts of carbon dioxide into the subsurface], we have the potential for activating faults," he said.
"The problem Zoback foresees is that the seismicity could create small pathways through the rock by which carbon dioxide would gradually seep back into the air. If the carbon dioxide permeates back out of the reservoir, the effort to keep it out of the atmosphere will have been futile," he said. In addition to failing to solve the problem, a lot of time and money would turn out to have been wasted."